Frequently Asked Questions

LED stands for light emitting diode. LEDs are classified as solid state devices and can withstand tremendous shock and vibration. High quality LEDs will last a lifetime when built into properly designed equipment. Let's compare LEDs to other types of lighting devices.

The common incandescent light works by passing a current through a fine wire - the filament. The current passing through the filament heats the wire to incandescent temperatures - 2800 to 3200°K. That is, the wire is so hot it glows. The incandescent light typically looks yellow-orange compared to noon day sunlight. The filament is relatively delicate at incandescent temperatures and can break if exposed to significant shock. or vibrations. Further, the filament slowly evaporates at those high temperatures, causing the filament to fail. Low wattage flashlight bulbs typically fail in under 15 hours and often fail just as the light is turned on as a result of high inrush currents due to a cold filament. Finally, the incandescent light is relatively inefficient with typical efficiencies in the 15 to 22 lumens per watt range.

The common fluorescent light and metal halide light are examples of arc lights. They work by passing a current through a gas enclosed in a glass tube. In the case of the fluorescent light, the gas contains mercury vapors and the interior of the glass tube is coated with phosphors to convert the UV light given off by the mercury to white light. These lights can generate light that looks very close to noon day sunlight. The final spectral content is controlled by the phosphors used. The glass tube is relatively delicate and can break if exposed to a significant shock. However, these lights are relatively efficient with typical efficiencies exceeding 60 lumens per watt.

The LED is a solid state device similar to a transistor. It is a solid block of material that is attached to the case. The current is passed though the material in the forward direction to make the material emit light. Although small bonding wires are often used to route current to the material, they are encapsulated in a clear material that re-enforces them and makes them very strong. The result is a rugged device that can withstand significant shock and vibration without damage. The latest LEDs are now exceeding 200 lumens per watt at medium power levels (early 2014) and can be expected to increase in efficiency by roughly 10% each year for the next many years.

Almost all of today's white LEDs work by combining blue light with yellow phosphors to generate white light. The die of the LED generates a blue light and when the blue light hits the yellow phosphor, the blue light is converted into green, yellow and red light. The final spectral content is controlled by the phosphors used. This allows for different tints of white and allows for special LEDs with a high color rendering index (CRI).

The Lumen is the international unit of luminous flux, which is a measure of the total "amount" of visible light emitted by a source. Luminous flux differs from power (radiant flux) in that luminous flux measurements reflect the varying sensitivity of the human eye to different wavelengths of light, while radiant flux measurements indicate the total power of all electromagnetic waves emitted, independent of the eye's ability to perceive it.

Your eyes are not uniformly sensitive to all colors of light. Your eyes are most sensitive to green light and least sensitive to violet and red light. The lumen takes the relative sensitivity of your eyes into consideration. The spectral content of light is multiplied by the sensitivity curve of your eye to create a final result. Thus, a milliwatt of green light (555nm) counts much higher in lumens than a milliwatt of violet light (415nm) or a milliwatt of red light (630nm).

Measuring lumens is difficult as it requires specialized equipment - namely an integrating sphere with calibrated spectrometer and special software. We start the measurement process by calibrating the spectrometer using a NIST (National Institute of Standards and Technology) traceable light source with a known spectral content. This calibration step is needed to account for measurement errors in the spectrometer. Then the light being measured must be broken up into the individual wavelengths and each wavelength must be accurately measured using the calibration data to correct any measurement errors. This results in a power spectrum. The power spectrum is then multiplied by the lumen sensitivity curve to generate a lumen spectrum. Finally, the lumen spectrum is integrated to generate a final calibrated lumen value.

A calibrated spectrometer can also be used to calculate the correlated color temperature (CCT), the color rendering index (CRI), CIE values and many other interesting numbers. We use a calibrated spectrometer for all of our LED and flashlight evaluations.

A light meter is not a calibrated spectrometer and cannot be used for accurate light measurement. A light meter is a single sensor behind a filter and can only take a single measurement. The filter and sensitivity of the sensor only roughly approximate the lumen spectral response. In fact, most light meters come with instructions on how to adjust the meter reading depending on the type of light source you have. Remember, light meters were designed for photographic and building illumination use so if you are off by half an f-stop (1.4x), it is no big deal because both film and the human eye are logarithmic.

The lumen is directly related to two other units of light measurement: lux and candela. A lux is the measure of illuminance, which means how much light is falling on a surface. The candela is the measure of luminous intensity, which means how much light is being emitted in a particular direction. These units of measure have the following relationships. A lux is one lumen spread over one square meter. A candela is one lumen spread across the solid angle of one steradian. The area at one meter distance from the point of a cone that occupies one steradian is one square meter. Thus one lumen is equal to one lux which is equal to one candela for one steradian at one meter from the source.

LEDs are tested after manufacture and sorted into bins. One of the bin categories has to do with how many lumens the LED will generate under a well defined set of conditions. For example, one manufacture places LEDs that generate from 87.4 lumens to 113.6 lumens at 350mA into their U bin and LEDs that generate from 113.6 lumens to 147.7 lumens into their V bin. The manufacturer allows a production tolerance of +/-10% for the measuring equipment. This means that the output of LEDs within one bin can vary over a 40% range.

It is common for a flashlight manufacturer to improve their flashlight's apparent output specification by claiming that they are generating the average bin lumens stated on the LED manufacturer's specification sheet. Or they may state the output specification as "up to" the maximum bin lumens stated on the LED manufacturer's specification sheet. Both of these are deceptive practices. This is referred to as spec sheet lumens.

An example will help you understand the deception of spec sheet lumens. Suppose we have an LED from a bin with a typical 40% spread - 180 lumens to 300 lumens. The average will be 240 lumens. The "up to" will be 300 lumens. And that is before we have taken losses from the optical system into consideration. In the end, you can end up with a 200 lumen flashlight being marketed as a 300 lumen flashlight. But wait, the deception gets worse.

The LED's spec sheet lumens are typically measured under ideal conditions at 25°C - before the LED has a chance to heat up. Once the LED operates at full power for a short period it will heat up and loose at least 20% of it's lumen output. So if the LED was from the bottom of the bin, you may find the LED is generating less than 50% of the claimed lumens under real conditions. The "up to" 300 lumens flashlight may only be generating 150 lumens - at the LED. Once you take the optical system losses into account, you may be getting 35 to 45% of the claimed lumens out the front of the flashlight. The "up to" 300 lumens flashlight may actually be emitting a mere 110 lumens out the front of the flashlight.

A better way to rate flashlights is to measure the light output after it has passed through the optical system and once the LED has had a chance to warm up. This is sometimes referred to as out-the-front (OTF) lumens. This is the method prescribed by the ANSI FL-1 standard. Unfortunately, the ANSI FL-1 standard allows you to perform the testing on 3 "representative" lights, which does not take care of the unit-to-unit variations between individual LEDs within the same bin. Two flashlights with the same lumen rating can still produce easily visible differences in output and be compliant.

HDS Systems is the only manufacturer to go the final step and calibrate each flashlight. We measure the output of each flashlight after it is completely assembled and adjust the output to produce the specified lumen output. This method allows the LED to warm up to operating temperature as part of the measurement process so the flashlight's true lumen output can be measured and adjusted under representative operating conditions. Thus, our 250 lumen flashlight can be counted on to actually produce 250 lumens.

ANSI is the American National Standards Institute and NEMA is the National Electrical Manufacturers Association. The ANSI/NEMA FL-1 standard is a basic performance measurement standard for flashlights. The standard specifies how testing should be performed and how results should be reported. HDS Systems uses the ANSI/NEMA FL-1 standard when measuring corresponding flashlight specifications.

Light output is measured using an integrating sphere with a spectral radiometer and is reported in lumens. Light output is measured 30 seconds after the flashlight is turned on to allow the LED to warm up.

Peak beam intensity is calculated from the measured illumination level at a specified distance and is reported in candela. Light output is measured 30 seconds after the flashlight is turned on to allow the LED to warm up.

Beam distance is calculated from the measured illumination at a specified distance and is reported in meters. The distance is the point at which the illumination level becomes 0.25 lux. Light output is measured 30 seconds after the flashlight is turned on to allow the LED to warm up.

Runtime is the time it takes the flashlight's output drops to 10% of the starting light output and is reported in minutes (<1 hour), hours and 15 minutes intervals (1 to 10 hours) or hours (> 10 hours). Standard rounding applies. The starting light output is measured 30 seconds after the flashlight is turned on to allow the LED to warm up.

Impact resistance is tested by dropping the flashlight on all 6 cubic orientations from the claimed height in whole meters. To pass, there must be no visible cracks or breaks and the flashlight must remain fully functional.

The water submersion rating is tested by submerging the flashlight to the claimed depth pressure for 4 hours. To pass, no water may enter the flashlight and the flashlight must be fully functional following the test.

The ANSI FL-1 standard defines beam distance as the distance at which the beam will illuminate a surface to 0.25 lux, which is equivalent to the amount of light from a full moon. The Inverse Square Law can be used to calculate corresponding distances for other levels of surface illumination.

The actual distance you can see not only depends on the levels of surface illumination, it also depends on how dark adapted your eyes are. If your eyes are adapted to a brightly lit scene, you will not even be able to see a surface illuminated to 0.25 lumens. If it was possible to know what your level of dark adaptation was, you could - in theory - use the inverse square law to find the distance that would result in a sufficiently high surface illumination for you to see an object.

The lumen-minute is a convenient concept for rating the efficiency of a flashlight. If you graph the output of a flashlight against time and calculate the area under the curve you can calculate the number of lumen-minutes produced by a flashlight for the period. The more lumen-minutes, the more light was generated by the flashlight and the more efficiently the light was generated.

When comparing two different flashlights there are two things to keep in mind. First, your eyes are logarithmic. That means that an increase in light output of 25% or a decrease of 20% is barely distinguishable and can safely be ignored. There needs to be a fairly large difference in output to make any operational difference when using a flashlight. Second, minutes of operation tend to be more valuable than absolute light output. Remember, your eyes will rapidly adapt to the existing light output and any visually small difference in light output will be muted by the adaptation.

In general, higher power settings are less efficient than lower power settings, with the efficiency dropping rapidly as you approach the maximum design limits for the LED, power supply and battery. At the maximum design limits you trade off a large percentage of your runtime for an almost imperceptible increase in brightness. This is because your eyes are logarithmic and the LED, electronics and battery performance are dropping at an N-squared rate. It is a loser's game to maximize output at any cost. Comparing the lumen-minutes will quickly show the folly.

Today's white LEDs generate white light by shining a blue light through a "yellow" phosphor. The blue and "yellow" combine to make white. We say "yellow" because the phosphor has a wide spectral emission that goes from green to red and thus appears to be emitting a yellowish light. The resulting shade of white - or tint - can vary significantly because of variations in the type of phosphor, the purity of the phosphor, the thickness of the phosphor layer and the spectral content of the blue light emitted from the die.

Achieving a consistent white color is very difficult to do with current LED technology and so each LED has a slightly different tint. From an aesthetics point of view, this can be annoying. If you compare two lights side by side they are likely to have two different tints - which always leads to the question of: which LED has the better tint? From a practical point of view, if both lights are used separately, each will work equally well and you may never notice that one or the other has a tint. From a personal point of view, everyone has a personal preference.

The color white encompasses a wide range of unsaturated colors and thus the color white can take on the tint of any color of the rainbow. We perceive a color to be white when it contains a sufficiently balanced mixture of colors to stimulate the three color receptors in your eyes. This can be done with only two colors but additional colors provide a much greater range of acceptable results and better color rendering.

If you take an object and heat it to incandescence, that object radiates a certain spectrum of light; That spectrum closely approximates the spectral emissions of a theoretical black body radiator heated to the same temperature. A black body is an object which absorbs all incident light and thus is black in appearance at room temperature. As you raise the temperature of the black body radiator, the incandescent color shifts from infrared to red to the blue-purple part of the spectrum along a curved line which is typically plotted on the CIE-1931 Chromaticity Diagram. This line is known as the Planckian black body radiator line.; "White" is generally considered to start at 2500°K

The best white colors lie along the Planckian black body radiator line in the range of 4000°K to 7000°K with typical noon daylight being in the range of 5500°K to 6500°K depending on how much northern sky light is included. Incandescent lights generally lie in the range of 2800°K to 3200°K and have a distinct orange cast when compared to daylight. The definition of white is the equal energy point that lies at x=0.333 y=0.333 on the CIE-1931 Chromaticity Diagram and corresponds to 5454°K.

The human visual system is very good at color-correcting the scene you are looking at to accommodate different "white" lights. As long as there is sufficient color information available, a white surface will take on a white appearance within a short time, even if the "white" light is far from the Planckian black body radiator line or far from daylight.

LEDs are available in a wide range of tint. The highest efficiency is achieve with the cool white tints - typically above 5500°K. The neutral white tints are typically in the 5500°K to 4000°K range. Warm white tints are below 4000°K.

The color rendering index (CRI) is an indication of a light's ability to reproduce a wide range of colors. The higher the CRI, the better the light can reproduce the full spectrum of colors.

The CRI represents the difference in spectral content between a measured light source and a black body radiator with the same color temperature and flux output and is tested using a special set of color samples. The maximum possible CRI is 100.

A typical cool white LED has a CRI around 72. Most neutral and warm white LEDs have a CRI around 82. Our high CRI white LEDs have a CRI of around 93. The differences between conventional LEDs and high CRI LEDs are quite dramatic when compared side-by-side. Skin, plants and even rocks take on a very natural tone and show much more vibrant colors.

The efficiency of a white LED depends on two different factors. The first is how efficiently the LED converts electricity into light. The second is how closely the white spectrum matches the sensitivity curve of your eyes. Remember, the lumen corresponds to the visible part of the spectrum multiplied by the sensitivity curve of your eyes. Your eyes are much more sensitive to green light than they are to red or violet light.

If you look at the spectral content of a cool-white LED, you will notice that a large percentage of the total output falls within the central part of the sensitivity curve of your eyes. So most of the cool-white spectrum adds to the lumen value. Typical cool white LEDs are weak in the red end of the spectrum and have a significant notch in the cyan part of the spectrum with a large spike in the blue part of the spectrum. This results in a color rendering index (CRI) of around 72.

On the other hand, if you look at the spectral content of a warm-white LED, you will notice that there is a significant part of the spectrum that lies to the right of the central part of the sensitivity curve of your eyes. That means there is much more red and infrared content in the spectrum. Unfortunately, much of this additional red and infrared content does not count significantly toward the final lumen value and thus effectively lowers the lumen output of the LED. This significantly lowers the overall efficiency of the LED but usually increases the CRI rating of the LED.

In between cool-white and warm-white is neutral-white. About the only thing you can safely say is that they will have lower efficiency and a higher CRI rating compared to cool-white LEDs. Unfortunately, you cannot make any blanket statements about efficiency or CRI compared to warm-white LEDs.

The phosphor conversion also contributes to the overall efficiency of the LED.

The LED in your flashlight will last for 6,000 to 18,000 battery changes depending on what brightness settings you are using. In practical terms, the LED in your flashlight will never need replacing.

The life of an LED depends on a number of factors. The most important of these are heat and current. Our flashlights have a direct thermal path from the LED to the exterior of the flashlight to remove any heat from the LED. Then we use a sophisticated regulation technique to manage the heat and current in your flashlight which will prevent premature aging that causes reduced lumens output and protects the LED from catastrophic failure.

Constant power regulation maintains a constant amount of power to the LED and hence keeps the light output constant as the battery is consumed. Further, constant power also does the best job of keeping light output constant in spite of temperature changes in the LED. HDS Systems invented the constant power regulation system to drive LEDs and HDS Systems is the only manufacturer in the world to use constant power regulation. Our power supply precisely matches the power available from the battery to the power required by the LED to keep the power - and light output - constant. And the power supply does this very efficiently.

The sophistication and quality of the power supply determines how well the regulation circuit can maintain the brightness at a constant value and how efficiently the battery power can be delivered to the LED. The really cheap lights use the simplest and least expensive circuits which tend to do a poor job of regulation and are inefficient. Better lights use more sophisticated circuits such as switching current regulators that do a better job. However, our switching power regulation circuits do the best job of keeping the brightness constant and are the most efficient.

Switching power supply circuits that raise the battery voltage are called boost regulators. Boost regulators raise the battery voltage when the LED requires a higher voltage than the battery is providing. Boost circuits require the battery voltage to be lower than the voltage required by the LED in order to properly regulate.

Switching power supply circuits that reduce the battery voltage are called buck regulators. Buck regulators lower the battery voltage when the LED requires a lower voltage than the battery is providing. Buck circuits require the battery voltage to be higher than the voltage required by the LED in order to properly regulate.

We use a third type of switching power supply circuit that can raise or lower the voltage to match the requirements of the LED. The advantage to this circuit is that it can accommodate different types of batteries with a wide range of voltages. And it allows certain battery, LED and power combinations that would not work with a pure boost or buck circuit.

We have added further sophistication to our regulation circuits to allow multiple brightness settings, reduced tint changes when dimming the LED, regulation of the LED temperature for higher efficiency, higher reliability and safety, detection and protection of rechargeable batteries and graceful step downs in brightness as the battery is used up so you have plenty of warning allowing you time to find a safe place to change batteries.

The efficiency of LEDs can vary significantly from one LED to the next, even within the same bin code. For the same amount of input power, the light output can vary by over 40% from one LED to the next. This difference is easily to see when two otherwise identical uncalibrated flashlights are compared side-by-side. Is the dimmer flashlight defective or is the brighter flashlight an over achiever?

We have chosen to calibrate each flashlight so that every flashlight has the same specified output. This results in consistant light output from one flashlight to the next.

The calibrated process starts by setting the maximum input power to the power that provides the minimum specified runtime. The LED must be able to make the required lumen output at the maximum power or it fails calibration. If the LED is an over achiever, the power is reduced until the output drops to the specified lumen output. Notice we are reducing power, which results in longer runtimes. Statically, flashlights will provide significantly longer runtimes than the advertised minimum runtime.

HDS Systems is the only flashlight manufacturer that measures the output of each flashlight after it is completely assembled and adjusts the output of each flashlight so each flashlight will produce the specified output. This method allows the LED to heat up to operating temperature as part of the measurement process so that the flashlight's true lumen output can be measured and adjusted under representative operating conditions.

Burst mode allows you to see with maximum visual acuity without sacrificing excessive battery life. Burst can also be used in combination with lower output settings to see much further than you would ordinarily be able to see.

Burst mode works because your eyes are logarithmic but the power to generate light is more linear. That is, in order to notice a small but visible change in brightness, you need to increase light output by 1.5x or decrease light output by 0.67x.

We can use an example to illustrate what is happening. Let's say you turn your light on to maximum - let's use 250 lumens for maximum in this example. The next brightness level down is 0.67x or 167 lumens. The difference is 83 lumens - which sounds like a lot. But remember, your eyes are logarithmic and only care about the ratio - not the absolute number of lumens - so your eyes see only a small difference in output. And most people don't even notice the step down.

Now look at what happens to battery runtimes. If you did not have burst, you would have 45 minutes of runtime before the light output dropped below 167 lumens - to 111 lumens. But by using burst mode, you get twice as long - an hour and 30 minutes before your light drops below 167 lumens - to 111 lumens. That is a huge increase in runtime - and utility.

In practical situations, you only need maximum output for a short period of time because your eyes will rapidly adapt to any excess of light. Burst mode operates at maximum for 40 seconds after you release the button before dropping one brightness level. And since maximum continues to operate for as long as the button is held down, momentary maximum will run for as long as you want it use it.

Think of the following situations where you hear a noise in the distance and turn the light on to maximum to identify what made the noise. If you identify a friend, there is no need to continue to blind your friend with a bright light. If you identified a foe, you will be running for your life or drawing your weapon within a few seconds. In either case, you only need absolute maximum for a relatively short period.

Your flashlight is much less efficient when producing the absolute maximum output compared to when it is turned down just one brightness level. This is due to a combination of battery, circuitry and LED characteristics that degrade at an N-squared rate. Thus, to maximize battery life, you want to limit the amount of time you spend using the absolute maximum output. Burst mode takes care of this automatically for you. After 40 seconds on maximum, the light steps down one brightness level. Although there is just a slight visual difference between the maximum output and the next level down, the difference in battery life is huge. And in most situations, you will probably not even notice the step down.

The brightness levels on our flashlights are spaced so that the difference between any adjacent brightness levels appear to be a small but equal change. This visual spacing takes advantage of the logarithmic nature of your eyes to see a huge dynamic range - from very bright midday summer scenes to dim moonlit scenes. Each brightness level is separated by a ratio of 1.5:1 - enough to provide a small but noticeable difference between brightness levels.

An optimal beam pattern is one that has a fairly bright center and then smoothly transitions to a dimmer outer area with an acceptable maximum contract ratio between the two. The brighter central area is used to look at more distant objects while the outer area of the beam allows you to maintain situational awareness by seeing objects outside of the central area. A smooth transition between the two is easy on your eyes.

Many manufacturers use a molded TIR (Total Internal Reflection) optical system, which is a combination transmissive/reflective system. These systems are inexpensive and they generally produce poor quality beam patterns with significant undesirable beam artifacts. It is very difficult using a TIR system to properly control the light distribution and prevent beam artifacts - which is why we don't use TIR systems.

We use a reflector to shape the light from the LED into a beam of light. A properly made reflector is very efficient at redirecting light from the LED into a beam of the desired shape.

Reflectors are normally parabolic is shape. A reflector starts with a theoretically perfect parabolic shape and a point light source and focuses all rays from that point source into a very tight beam of parallel rays. This results in a tiny spot of light even at great distances. A tiny spot of light may be great for looking at a distant bird but that same tiny spot of light is not practical for most medium range uses.

Creating an optimal beam pattern requires adding a controlled amount of error to the optical system. You can add error by increasing the size of your point source. You can also add error by reducing the size of the parabolic surface. You can also add error by adding surface imperfections to the parabolic surface - either at a macroscopic or microscopic level.

The size of the LED die combined with the size of the parabola sets the limit on how tight a beam can be - and thus how far the beam will throw with a given amount of light. But as we have seen, we often want to add additional error to the parabolic surface to achieve a more useful distribution of light within the beam. Surface coatings are one way to increase the surface error.

Surface coatings are often used to add a small but predictable amount of error to a parabolic surface. This serves to diffuse the baam pattern and smooth transitions in a controlled fashion. This can be done on the macroscopic scale using a technique such as orange peel, which is easily visible when looking at the reflector. It can also be done on the microscopic level, in which case it may be impossible to see without using a microscope.

The process we use involves a microscopic coating. It is a fairly thin coating applied directly over the anodized machined aluminum surface. This surface shows a network of fine bright lines when the light is on a low setting and you look diagonally into the reflector. The lines are actually the edges of the anodize plates - really tiny cracks that are part of any military type 3 hard anodized surface. They are completely normal and do not affect the output or beam pattern.

There are two common ways to dim an LED. The first way to dim an LED is to turn the LED on and off very rapidly at full power. If the light is off for 50% of the time, you will perceive the light to be half as bright. This is called PWM (Pulse Width Modulation) and results in an annoying flicker - especially at low light levels. It also results in lower overall system efficiency.

The second common way to dim an LED is to reduce the current flow. However, as the current is reduced, the tint of the LED can shift toward the green part of the spectrum.

We use a more sophisticated algorithm for dimming the LED that minimizes both the amount of tint shift and the annoying flickering while increasing the total system efficiency.

Acme threads are trapezoidal thread forms that are superior in every respect to the conventional V thread forms used in most products. Acme threads are stronger, less likely to cross-thread and will last much longer than conventional V threads. Acme threads are used in precision machinery and in applications requiring the most robust threads available.

We use Acme threads throughout our lights because they are the best threads available.

The purpose of a lens is to transmit as much light as possible. As the light passes though an untreated air/lens surface, roughly 5% of the available light is reflected back. This reflected light is wasted. A glass lens has two air/lens surfaces - one on each side of the lens and thus 10% of the light can be lost.

In addition to using ultraclear glass for our glass lenses, we apply an anti-reflective coating to both lens surfaces to reduce the amount of reflected light and thus increase the amount of light transmitted through the lens. Both surfaces are coated to maximize the amount of light the lens can transmit. This increases the efficiency of your flashlight and allows 97% of the light to be transmitted out the lens.

An anti-reflective coating is a vapor deposition coating that is applied in a vacuum. The coating is a fraction of a wavelength of light thick and acts like a tuned circuit in electronics to match the "impedance" between the lens and the air. This allows the lens to capture and transmit the light that would otherwise be reflected.

The anti-reflective coating is fairly durable but it is very thin. Excessive rubbing will abrade the coating on the exterior surface. Paper-based towels are very abrasive and should never be used to clean or wipe the lens. Flushing the lens under running fresh water and then blowing or shaking off any remaining water is best. However, even if you rub off the coating or it becomes soiled and stops working, you will only reduce the output by a small amount - which is not significant.

Anodize is a hard protective coating formed on the surface by a special electrochemical process. In the case of aluminum, the layer is a crystalline form of aluminum oxide and is similar to synthetic sapphire (corundum). The anodize is very hard and becomes quite scratch resistant when the layer of anodize is thick enough.

There are two common types of anodize used to protect aluminum products. The first is a thin clear decorative coating that can be dyed vibrant colors. This is called Type 2 anodize. Although the layer is very hard, it is very thin and relatively delicate. A sharp object can easily penetrate the layer and cause a scratch in the coating. Also, because the layer is so thin, it will be rubbed through in a relatively short period of time.

The second common type of anodize is called Type 3 or hard anodize. This is a thick dark olive coating that is very scratch resistant and wears well. This coating is often referred to as military hard anodize. Although Type 3 anodize can be dyed, colors other than black are not used because other colors come out muddy and very dark.

Type 3 anodize can vary in color from a medium gray to a dark olive before it is dyed. This color variation is common and normal - even within the same batch of parts. Slight variations in current density, bath chemistry and even temperature will affect the final color. Adding black dye dramatically reduces the color variations - and the resultant complaints about color matching.

Type 3 anodize can also vary in surface smoothness. The surface texture is a result of the final machining operation and the processing steps just prior to the anodize step. Variations are normal - although we attempt to keep the variations to a minimum. The typical appearance is a shiny black surface.

Black nitride is a military coating that both hardens the surface of stainless steel and turns it "black". The typical black nitride finish has a matte dark brown appearance. It is also possible to see copper-colored patches due to variations in the underlying material. It is also possible to see tiny silvery spots due to variations in the underlying material. These are purely cosmetic and have no effect on the part and are considered normal.

We use black nitride to provide a black coating on our stainless steel bezels, stainless steel rotary control switch caps and stainless steel pocket clips. The coating is very durable.

Cerakote is a brand of high performance coatings. We use the H-series two-component baked ceramic finishes designed for firearms and firearm accessories. The Cerakote H-series finishes provide an abrasion resistant high quality finish.

Ceramic is a tough material. The Cerakote baked-on ceramic finish is tougher than similar one-component room-temperature coatings, powder coats or paints. Although the baked ceramic coating is tough, it is not as tough as military Type 3 hard anodize. The finish can chip if dropped on a hard surface.

We apply Cerakote directly over a prepared military Type 3 hard anodize finish for the aluminum parts. The anodize provides a solid base for the application. We apply Cerakote directly to our stainless steel bezels after appropriate surface preparation. As with any finish application, careful preparation and craftsmanship are required for quality results.

Cerakote H-series is available in a wide range of colors. We offer a small subset of those colors. See our Custom-built flashlight page for a list of currently available colors.

Your eyes respond to light in a logarithmic way. That means they require a significant percentage change in light output for your eyes to notice a small but visible change in brightness. A 50% (1.5x) increase or 33% (0.67x) decrease will produce a small but visible change in brightness. An increase or decrease of half that - 25% (1.25x) and 20% (0.80x) respectively - will probably not be noticed.

You are probably already familiar with logarithmic scales in other areas of your life. For instance, earthquakes are measured using the logarithmic Richter scale. Sound is measured in logarithmic decibels. If you are a photographer, you are familier with the logarithmic f-stops and the logarithmic progression of shutter speeds. Even the musical notes in an equal temperament scale are logarithmically spaced. Logarithmic scales make it much easier to represent very large variations from tiny to huge because the scale represents a progression of ratios instead of a progression of linear units. The perception of most physical phenomena by our bodies - sight, sound and touch - are essentially logarithmic. It is difficult for us to perceive small percentage changes.

Many people are surprised to find out that going from 0.17 to 0.25 lumens looks the same as going from 167 to 250 lumens. From your eye's perspective, the step size is the same in both cases - a small but visible change. Notice that in the first case we only increased by 0.08 lumens while in the second case we increased by 83 lumens - a difference of 3 orders of magnitude.

You might be surprised to find out that you need a 10x increase in light to produce what most people consider to be a doubling in the amount of light. Again, this is due to the logarithmic nature of your eyes.

Your eyes respond to light in a logarithmic way. That means they require a significant percentage change in light output for your eyes to notice a small but visible change in brightness. A 50% (1.5x) increase or 33% (0.67x) decrease will produce a small but visible change in brightness. An increase or decrease of half that - 25% (1.25x) increase and 20% (0.80x) decrease - will probably not be noticed.

So what is the practical difference between two flashlights with different outputs? If the difference is small - around 25% - you will probably never see the difference. If the difference is larger - around 50% - you will see the difference but it will be a small difference - and if you are not paying attention, you may miss it. If the difference is much larger - around 100% - it will be easy for you to see the difference, but you may be surprised that it does not appear to be larger.

Here are some examples. The average person will not notice the difference between 140 and 170 lumens, 170 and 200 lumens, 200 and 250 lumens or 250 and 325 lumens. However, you will notice the difference between 140 and 200 lumens, 170 and 250 lumens or 200 and 325 lumens.

Keeping the same 1.5x ratio, and starting at 325 lumens, you would have to increase the output to 488 lumens to produce a small but noticeable increase in brightness.

The practical reason for having a higher output flashlight - even if you do not think you really need that much light - is that the lower output settings will have much longer runtimes. With our flashlights, the runtime for a given level is the same across all models even though the outputs may differ significantly. For instance, you can use level 16 on a 325 lumen flashlight to produce the same output at lever 17 on a 200 lumen flashlight or level 18 on a 140 lumen flashlight. The lower the level number, the longer the runtime. It's that simple.

There is no one "best" beam pattern for all situations. For instance, focusing all the light into a very narrow beam may be perfect for looking at an object at great distances. However, it is lousy for walking across rugged terrain because the central beam illuminates a very small area and the contrast is too high to see anything outside of the central beam. Conversely, a flood light is great for evenly illuminating a large field of view at close range but is lousy for seeing something distant.

The Inverse Square Law of light tells us that if we double the beam width we can only see half as far but we can see four times the area compared to the original beam - assuming the same surface brightness at both distances.

The optimum beam pattern is the one that is most useful for your application. This requires a balance between the light in the center of the beam and the light in the outside of the beam and an appropriate transition between the two. For instance, it is better to have a beam with a soft transition from the center to the edge and a relatively low contrast ratio across the beam for a headlamp or use in rugged terrain. For general flashlight use, having more light toward the center of the beam is often desired.

The beam pattern can have a significant effect on the apparent brightness of a flashlight when comparing two flashlights having the same lumen output. A narrower beam will appear brighter and throw further while a wider beam will appear dimmer and have a shorter throw but wider spot.

The following table provides the theoretical output for each brightness level. The last digit has been rounded. The difference between all adjacent brightness levels is visually even. That is, all level changes appear to be of equal size to your eyes. Remember, your eyes have a logarithmic response to light, requiring a roughly 1.5:1 change in order to register a small but visible change in brightness.

We provide runtimes for many brightness levels.

The following table shows the minimum ANSI FL-1 runtime for each brightness level. The ANSI FL-1 runtime is defined as a drop to 10% of the original brightness, which corresponds to a drop in 6 brightness levels. Level 24 is tested with Burst disabled. Level 23 is tested starting with level 24 with Burst enabled so the resulting runtime is slightly shorter than if the test had started with level 23.

The table provides information for several representative battery configurations. The tests were done with new premium batteries on an integrating sphere at room temperature. Per the ANSI FL-1 standard, runtimes under an hour are rounded to the nearest minute, runtimes from 1 to 10 hours are rounded to the nearest 15 minutes and runtimes over 10 hours are rounded to the nearest hour.

Tactical runtimes are listed in parentheses for levels that are normally tactically bright. The tactical runtime is defined as the runtime down to 50 lumens. The tactical runtimes listed assume level 21 is above 50 lumens and level 20 is below 50 lumens.

Data is shown for a sampling of brightness levels. You can extrapolate the runtime data for other levels by using the ratio of 1.5:1 to estimate the runtime differences between adjacent levels.

The efficiency of LEDs vary from one LED to the next. Therefore the amount of power it takes to generate the same amount of light will very from one LED to the next. We have chosen to hold the light output constant from one flashlight to the next. This results in constant light output but causes variations in runtimes from one flashlight to the next. We specify a minimum runtime at the rated light output. This results in a statistical distribution with the typical runtime being 10 to 15% higher than the minimum runtime.

The type of battery used will have an impact on flashlight runtime. The most significant difference in batteries is how they handle the highest power levels. You should always choose premium batteries that can handle high continuous currents.

Temperature can also have a significant impact on flashlight runtime. As the battery temperature drops, the performance of the battery will deteriorate. How much power is lost with temperature depends on many factors, including battery chemistry and output. Lithium chemistries are preferred for cold environments.

We are going to show you a simple method to take advantage of how your eyes work and how your flashlight works to see the furthest possible distance - further than you can see with other flashlights with the same output rating. But first, you need some additional information so you understand how this method works.

The first thing to understand is that your eyes are marvelously adaptive. If you expose your eyes to a brightly lit scene, they will reduce their sensitivity to light - effectively throwing away the excess light. On the other hand, if you expose your eyes to a dimly lit scene, your eyes will increase their sensitivity to light - effectively becoming more efficient at gathering the available light. Thus, you want to use an appropriate amount of light for your task without over illuminating the scene.

The second thing to understand is the Inverse Square Law - it takes 4 times as much light to see twice as far - all else being equal. This is because at twice the distance the light has spread out over 4 times the surface area and is thus 1/4 the brightness. So to illuminate the distant surface to the same brightness level, you need 4 times the amount of light.

And finally, your eyes are logarithmic in their response to light. In simple terms, if you double the amount of light you will see a small but easily recognized increase is brightness. This is true whether the increase is from 1 to 2 lumens or 100 to 200 lumens. They both appear to be equal increases to your eyes. The change in output between levels on our flashlights are visually even and are separated by 1.5x increases for a small but noticeable difference.

In practical terms, this means you can increase the output by one level (1.5x) and see 22% further, two levels (2.3x) and see 50% further, 3 levels (3.4x) and see 84% further or 4 levels (5x) to see 125% further - over twice as far. This assumes the same level of dark adaptation has been maintained.

We will use two scenarios to illustrate the best use of your flashlight and how using this new technique will allow you to see much further than you can see with an ordinary flashlight.

In the first scenario, you turn your light on to the maximum setting and go for a walk. After 40 seconds, your flashlight will automatically steps down to one setting lower to maximize runtime without making a significant visual difference. Most people do not notice the step down under typical conditions of use. It is difficult to not over illuminate the area just in front of you so you will have a compromised level of dark adaptation. As you are walking along, you hear a noise so you point your light at the noise. Pressing the button will reactivate the maximum output allowing you to see 22% further than without it. In any case, the distance you can see is limited by your compromised dark adaptation.

For the second scenario, we will assume you use a much lower setting to take your walk - perhaps just a fraction of a lumen. If you point the light a few body lengths in front of you, you have plenty of light to see with and you maximize your dark adaptation. Again, you hear the noise, point the light at the noise and push the button. But this time, you can see over 5 times as far as you can see before pushing the button. That certainly sounds impressive but can you really see any further than in the first scenario?

The answer is yes - by a large margin. The absolute maximum light output is the same in both scenarios so why can you see further in the second scenario? The answer is dark adaptation. With the bright light in the first scenario, it is difficult to avoid over illuminating the scene and ruining your dark adaptation. With the dim light in the second scenario, it is easy to build your dark adaptation, which counts as several additional brightness levels when you turn on the maximum output. Two additional brightness settings allow you to see 50% further. Three brightness settings allow you to see 84% further. Four brightness settings allow you to see 125% further - that's over twice as far.

During the second scenario you have not asked your eyes to suddenly increase their dark adaptation - which they cannot do anyway. By allowing your eyes the opportunity to adapt to lower light levels and then working with that level of dark adaptation, you have significantly increased the effective range of your flashlight. And thus, a 5x increase in distance is easily obtained while 20x is possible with high dark adaption.

The other benefit from the second scenario is runtime. In the first scenario, you will be replacing your battery in a couple of hours. In the second scenario, you can stay out several nights without needing to change your battery.

Smoke, fog and murky water have one thing in common - they are all composed of tiny particles suspended in a medium. Smoke is composed of incomplete combustion particles suspended in air. Fog is composed of tiny water droplets suspended in air. Murky water is composed of tiny particles such as silt or tiny organisms suspended in water.

The suspended particles are reflective to a certain degree. The particles have irregular shapes with a random orientation to the light source producing a scattered reflected light pattern. The distribution of the scattered reflected light produces a characteristic bell curve shape with the maximum reflectivity being on axis to the beam and the lowest reflectivity being far off axis.

This tells us we should move the light as far off our viewing axis as possible to minimize the reflected light from the suspended particles. Reducing the scattered light from the suspended particles will increase the contrast between the light reflected from the object we are trying to see and the glow of the scattered light from the suspended particles - thus making it easier to see the object.

In other words, hold your light out at arm's length perpendicular to your line of sight to minimize the glow from suspended particles. In the case of smoke and fog, both tend to be less dense near the ground - i.e., there are fewer suspended particles close to the ground. Thus, holding your light as low as possible will further reduce the glow from suspended particles.

If you ever get caught in a building fire, consider crawling on your belly so you can access the coolest and least smoky air.

Forensic lights are used to see bodily fluid residues. The reason they work is that most bodily fluid residues contain fluorescent compounds. The forensic light emits a light that causes the compounds to fluoresce. Bodily fluid residues that contain a higher concentration of these compounds - such as urine residues - show up much better than other residues.

Both blue and ultraviolet lights can be used to excite most fluorescent compounds. Blue has traditionally been used in forensic lights because it offered a less expensive and more compact solution to achieve the same visual result.

With forensic blue, orange glasses are required to remove the blue emission so you can see the much fainter green, yellow and red fluorescent emissions. If the residues are on a blue reflecting surface, the reflected blue light will mask the fainter fluorescent emissions - so the blue emissions must be removed - thus the orange glasses.

With a UV black light, no orange glasses are required as you cannot see the 365nm emission. Thus, the only emissions you will see are the result of fluorescent emissions. You may be surprised that you can see skin and plant tissues with UV - because they contain fluorescent compounds and thus fluoresce to a certain degree.

However, it should be noted that orange glasses may still be needed with UV lights if the bodily fluid residues are on a white material that exhibits a strong blue fluorescent emission.

Dim to dark conditions are required in order to observe fluorescent emissions. Any significant amount of ambient light will overpower and mask the fluorescent emissions.

Bathrooms and kitchens are great places to begin your investigation of residues.

If you use your flashlight on a regular basis, the cost of ownership is primarily a function of the hourly cost of operation. Efficiency and best practices are the keys to maximizing battery life and obtaining the lowest cost of ownership without sacrificing the utility of your flashlight.

An example will illustrate how this works. For this example, we will assume a premium battery costs $1.75.

Let's consider a 250 lumen EDC LE, which will run for 3.25 hours on the tactical brightness setting before dropping below 50 lumens. This yields an operating cost of $0.54 per hour ($1.75/3.25 hours). In 100 hours, the EDC LE will cost you $54 to operate. If we add in the price of the flashlight ($199), the total cost of ownership for the first 100 hours is $253.

Now let's take a typical 2 battery incandescent tactical flashlight. You can usually get 1 hour of operation at 65 to 75 lumens before you have to replace the batteries. This yields an operating cost of $3.50 per hour for the batteries. Plus you will have to replace bulbs at least once per 15 hours at $15 each for an operational cost of $1.00 per hour for bulbs. In 100 hours, the 2 battery incandescent tactical flashlight will cost you $450 to operate. If we add in the price of the flashlight ($65), the total cost of ownership for the first 100 hours is $515.

Notice that the less expensive 2 battery incandescent tactical flashlight has twice the cost of ownership in the first 100 hours - even though the EDC LE purchase price was three times higher. The EDC LE is far less expensive to own and operate compared to a typical 2 battery incandescent tactical flashlight.

The cost of ownership becomes even more exaggerated when comparing most flashlights to the 250 lumen EDC Executive. The EDC Executive 250 lumen flashlight operating cost is a mere $0.07 per hour ($1.75/24 hours) - or $7.30 for the first 100 hours of operation. The total cost of ownership for the first 100 hours - including the $199 purchase price - is $207.

The cost of ownership can be reduced even further by using rechargeable lithium-ion batteries. Even if you replace the rechargeable batteries on a regular basis, you are only looking at pennies per hour operating expense for the EDC LE and a fraction of a penny per hour operating expense for the EDC Executive. Now that is a truly low cost of ownership.

We do not overdrive our LEDs. Our advanced technology allows our lights to provide superior light output without overdriving the LED.

We do not overdrive our LEDs because overdriving an LED produces excessive heat, reduces the efficiency of the LED, reduces runtimes, reduces the reliability of the LED and rapidly ages the LED - which permanently reduces light output.

For maximum reliability and safety, we monitor and regulate the temperature of the LED. Heat is the primary enemy of your LED and so regulating the LED temperature prevents premature aging, increases reliability and increases efficiency. In addition, regulating the LED's temperature prevents the flashlight from becoming dangerously hot and injuring someone who touches it.

Your flashlight protects itself from becoming too hot to safely handle. Even though we do not overdrive the LED, there is still enough heat generated on the highest settings to raise the temperature of the light to potentially dangerous levels. Thus, your flashlight keeps track of the temperature of both the LED and the exterior of the flashlight and reduces power when necessary to prevent your flashlight for getting too hot.

If you have disabled Burst mode, level 24 will run for roughly 4 minutes without a thermal path before power is automatically reduced to keep the LED and your flashlight in the safe temperature range. If you provide a thermal path, such as holding the flashlight loosely in your hand, your body can draw away sufficient heat to prevent the your flashlight from automatically reducing power. Note that Burst mode automatically reduces power long before the thermal power reduction would automatically take place.

Level 23 will often run continuously without needing to reduce power even without a good thermal path - for instance, while sitting on the table. However, should it be necessary, your flashlight will automatically reduce power.

Level 22 and below do not generate enough heat to require power reductions under normal conditions.

There are several ways to attach a lanyard to your flashlight. All of our accessory pocket clips come with lanyard attach points. However, if you are not a fan of pocket clips, you can use a universal lanyard attachment or a secure knot such as the Constrictor Knot.

The Constrictor Knot is a simple secure knot that can be tied around the waist of the battery compartment and the ends can be made any length required. As with many knots using wraps, you can use one or more wraps. The photo to the left (David J. Fred, 2006) shows a regular (1 wrap) Constrictor Knot on the left and a double (two wrap) Constrictor Knot on the right. The double Constrictor Knot is recommended.

Think of the Constrictor Knot as an Overhand Knot with the wrap(s) passing over the knot.

The length of time your battery will last is referred to as the runtime and is dependent on several factors. We have posted a table of runtimes so you can compare the runtimes on various levels using different battery configurations.

We provide two different runtimes - tactical runtimes and ANSI runtimes. We always list the ANSI runtime, which is defined as the runtime down to 10% of the original lumen output. If a particular setting produces over 50 lumens, we also list a tactical runtime, which is defined as the runtime down to 50 lumens.

The tactical runtime is a shorter and more realistic runtime for someone using a flashlight in tactical applications - such as law enforcement, security patrol or self-defense - conditions under which only tactical levels of light are acceptable. The ANSI definition of 10% is just too dim to be useful for tactical situations.

HDS Systems is the only manufacturer to calibrate flashlights to a specified lumen output. Efficient LEDs need less power to generate the calibrated amount of light and will have longer runtimes as a result. Our specified runtimes are minimum runtimes with typical runtimes being longer. If a particular light cannot be calibrated to the specified lumens while meeting the minimum runtime, it will be calibrated to a lower lumens specification in order to meet the minimum runtime and sold as a lower output flashlight.

The calibration process ensures the minimum runtime is always met. However, the actual runtime is typically better than specified.

Battery performance is dependent on several factors including battery chemistry, power draw and temperature. Premium quality batteries are required to get full performance from our flashlights. Poor quality batteries will result in poor performance - it's that simple. Low temperatures will reduce a battery's performance. Lithium batteries will continue to work down to -40°C (-40°F) but their performance is significantly reduced by that temperature. Battery performance peaks a bit above body temperature.

Power draw has a significant affect on battery capacity and runtime. As a rough approximation, every two levels brighter will halve the battery life and every two levels dimmer will double the battery life. You can maximize battery life by using the lowest brightness level compatible with the task you are performing. The lowest brightness level will help preserve your dark adaptation without using a red filter.

The main difference between primary lithium and rechargeable lithium-ion batteries is that primary lithium batteries are used once and thrown away while rechargeable lithium-ion batteries can be used and recharged hundreds of times. This can make a dramatic difference in the overall cost of operation of your flashlight. If you assume $1.67 for primary lithium batteries and $54.00 for two rechargeable lithium-ion batteries and the charger, the break even point is at 32 primary batteries.

Another significant difference between primary lithium and rechargeable lithium-ion batteries is the voltage. The voltage for primary lithium is about 3.2V before it is used and roughly 2.8V when being used. The voltage for a rechargeable lithium-ion battery is 4.2V when fully charged and roughly 3.6V when being used.

Rechargeable lithium-ion batteries have a lower power capacity than primary lithium batteries of the same size. However, you can swap a partially used rechargeable lithium-ion battery for a fully charged one so you always leave home with a full capacity battery. People that use primary lithium batteries usually find it too expensive and wasteful to put in a fresh battery until the current battery is mostly depleted. Thus primary lithium battery users often leave home with less available runtime than if they had used rechargeable lithium-ion batteries.

Primary lithium batteries will retain more total capacity at lower temperatures than rechargeable lithium-ion batteries. And primary lithium batteries will operate to lower temperatures than rechargeable lithium-ion batteries.

Primary (disposable) lithium batteries are an advanced battery chemistry that economically out-performs most commonly available battery chemistries under high drain and cold temperature conditions. And all this is available at a very attractive price point.

The 123 size lithium battery was originally designed for high current camera applications but they also excelled in flashlight applications where their small size and high power provide unrivaled levels of product performance. Other names for this battery size are 123A, CR123, CR123A, ANSI/NEDA 5018LC and IEC CR17345.

Lithium primary batteries use the Lithium-Manganese Dioxide (Li-MnO2) chemistry. They provide a high output voltage of 3.2V (2.8V nominal), have a 10 year shelf life and continue to operate below -20°C with reduced capacity.

Dead batteries are safely disposed of in a sanitary land fill. Check with your local authorities for local disposal requirements.

Rechargeable lithium-ion (Li-ion) batteries provides you with a dramatically lower cost of operation for your heavily used HDS Systems EDC flashlight while at the same time allowing you to always head out the door with a full capacity battery. Lithium-ion batteries can be conveniently recharged when only partially used without any detrimental affects such as the memory problems that plague Ni-Cad batteries.

Our flashlights are designed to accommodate the higher voltages generated by rechargeable lithium-ion batteries - up to 4.2V when fully charged, 3.6V nominal. In addition, our flashlights automatically detect lithium-ion batteries and protect them from over-discharge when used as directed. These two features are unique to our line of flashlights and make using lithium-ion batteries safe and convenient.

There are three different lithium-ion battery chemistries compatible with our flashlights - often designated as ICR, IMR and INR.

The oldest and most common lithium-ion battery chemistry is know as ICR - Lithium Cobalt Oxide (LiCoO2). This chemistry requires a protection circuit to be used safely due to the chemistry's inherent instability. The advantage of this chemistry is its higher total capacity - allowing 50% greater capacity in the larger battery sizes compared to the IMR and slightly higher capacity compared to INR chemistries. The disadvantages are the required protection circuit increases the battery size, lowers the total performance at high discharge rates and adds another failure mode to the battery system.

A more recent lithium-ion battery chemistry is the very safe chemistry known as IMR - Lithium Manganese Oxide (LiMn2O4). In fact, this chemistry is considered safe enough to use without a protection circuit and is thus more reliable when used in harsh conditions, such as gun mounted applications.

The newest lithium-ion battery chemistry is the very safe chemistry known as INR - Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2). This chemistry combines the safety of the IMR chemistry with the capacity of the ICR chemistry. And no protection circuit is required, making this a very reliable battery. We believe this is the battery chemistry of choice going forward.

We have designed our flashlights to prevent battery over-discharge and thus our design also prevents the protection circuit from activating. In other words, our design prevents sudden unexpected darkness.

When the battery protection circuit detects the battery is being over-discharged, the protection circuit turns off the battery to prevent further discharge - which causes the device containing the battery to suddenly stop working without warning. This is no different than a catastrophic failure of the device. The battery will remain off until it is recharged, leaving you with no light and no options. This is how our competition designs their flashlights.

It is dangerous to simply turn off the flashlight unexpectedly to prevent over-discharge. Instead, our flashlights reduce the output brightness as the battery is discharged. When the lowest brightness is reached, your flashlight will begin to blink about once a second. When your flashlight begins to blink, you should immediately find a safe place to change your battery, wait for the sun to come up or wait for rescue. Your light will continue blinking for a short unspecified amount of time before the voltage reaches a critical level for the battery and your flashlight turns off to preserve the battery - and your options. You can turn your light back on again for another short burst of light as needed. A tiny amount of light is far better than no light at all.

The smaller 123 size rechargeable lithium-ion batteries provide less emergency time than primary (non-rechargeable) batteries due to their lower total capacity. That means that once your flashlight begins to step down to lower brightness levels as the battery is used up, the step-downs will occur more rapidly and you will have significantly less time before the light becomes very dim compared to primary batteries. So we recommend you immediately take action to reduce output and find a safe place to change your battery.

Rechargeable lithium-ion batteries should be replaced every few years, regardless of how much you use them. Three years of normal use will reduce the capacity of batteries by roughly 20%. The only way to know the current capacity of a battery is to perform a metered discharge test.

Batteries age and slowly loose their capacity. Keeping a battery fully charged and ready to use ages a battery. Using a battery - first discharging it and then recharging it - ages a battery. The aging process is minimised if the battery is left partially charged at roughly 3.85V and not used - which is how the battery is shipped from the manufacturer. However, that level of charge is only useful for long term storage - not for everyday use.

Rechargeable lithium-ion batteries are sensitive to temperature. Higher temperatures accelerate aging and contribute to the permanent loss of capacity. Lithium-ion batteries may be used from -20°C (-4°F) to 50°C (122°F). However, they should be brought to room temperature before recharging - from 15°C (59°F) to 35°C (95°F).

Do not be afraid of swapping a lightly used battery for a fully charged battery. This allows you to leave home with the maximum available runtime.

Lithium-ion batteries require special chargers that are designed for the battery being charged. In general, lithium-ion batteries should never be charged at a rate that exceeds half of their rated capacity and the maximum terminal voltage should never exceed 4.2V. You should only use a high quality 4-phase (TC/CC/CV/off) charger to charge your batteries.

Do not use the new IFR - Lithium Iron Phosphate (Li-FePO4) batteries with our products. Although this is a very safe battery chemistry, it cannot be reliably distinguished from a primary lithium battery and handled appropriately - leading to unreliable behavior and possible damage to the battery.

The 123 battery size is known by many names including 123A, CR123, CR123A, ANSI/NEDA 5018LC and IEC CR17345 and these names normally are used for primary (non-rechargeable) batteries. Putting an R in front of the name is a common way to distinguish a battery as a rechargeable battery. Thus the common designation of RCR123 is just a rechargeable 123.

Rechargeable batteries in the 123 battery size are always lithium-ion (Li-ion) batteries.

In the international cell size designations, the first two digits are the diameter in millimeters and the last three digits are the length in tenths of a millimeter. Thus an IEC CR17345 battery will be 17mm in diameter and 34.5mm long. It is common usage to shorten the IEC designation to just the 5 digits - i.e., 17345 instead of IEC CR17345.

A typical rechargeable lithium-ion battery is manufactured using a 16340 or shorter cell. By the time you add the protection circuit, power strap and shrink wrap label, the resulting battery grows to the 17345 (123) size. Many battery vendors sell their batteries listing their battery size - incorrectly - as the smaller (pre-finished) cell size. Thus rechargeable 123 batteries are often advertised as 16340 batteries. This causes a great deal of confusion.

The 18650 is the naked lithium-ion cell used to build the finished 18680 or 19680 battery.

In the international cell size designations, the first two digits are the diameter in millimeters and the last three digits are the length in tenths of a millimeter. Thus an IEC CR18650 battery will be 18mm in diameter and 65.0mm long. It is common usage to shorten the IEC designation to just the 5 digits - i.e., 18650 instead of IEC CR18650.

A typical 18680 rechargeable lithium-ion battery is manufactured using a 18650 cell. By the time you add the protection circuit, power strap and shrink wrap label, the resulting battery grows to the 18680 size or even the 19680 size. The actual finished size can vary quite a bit. Many battery vendors sell their batteries listing their battery size - incorrectly - as the smaller (pre-finished) cell size - i.e., 18650. Thus rechargeable 18680 and 19680 batteries are often advertised incorrectly as 18650 batteries.

This is the core of the problem. If a battery compartment is design for an 18mm diameter battery and you purchase a battery advertised to be 18mm but which is actually 19mm diameter, it probably will not fit. This is both confusing and aggravating for the customer. We sell AW brand batteries because they are actually 18mm in diameter and are of the highest quality.

It is useful to understand that the size designation confusion has it's roots in the evolution of batteries used in flashlights. When 18650 batteries first came out, they were sold by manufacturers to build into equipment - such as laptop computers. They were never intended to be sold to consumers directly. In the flashlight industry, the hobby builders started using them without any protection circuits for their tricked out lights - partly because there were no cells with built-in protection circuits at the time. By the time protection circuits were being added to batteries and the batteries because available to the general public, the common usage had already been in place for a few years and so many of the resellers simply followed suit, retaining the older and now incorrect size designations.

Our battery compartments are designed to use 18680 batteries - that is, protected batteries built around a 18650 cell. Please note that not all 18680 batteries are created equal. We use premium quality batteries built around slightly smaller diameter cells with thin connector straps and shrink wrap to minimize battery bulk. The batteries we sell will fit our battery compartments. However, less expensive batteries often use larger cells, thicker straps and thicker shrink wrap and will not fit our battery compartments. Never force a snug fitting battery into the battery compartment.

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

• Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
• Unscrew the head from the battery compartment. Set the battery compartment aside.
• The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
• Reflector stays with the head. Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
• Reflector stays with the bezel. Set the head aside, LED side up. Using a strap wrench, unscrew the reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
• If the upper O-ring is not on the lens, carefully remove it from the bezel and set it on the lens directly above the lower O-ring.
• Carefully place the new bezel over the stack and screw it down. Ensure that the O-rings sit in their little grooves and do not come out and get pinched. If the reflector stayed with the bezel during disassembly, lift the stack off the table keeping it in the same orientation and place it on the head and screw the reflector into the head. Tighten everything by grabbing the bezel and head. You only need to tighten until the gaps between the bezel, reflector and head are gone - do not over tighten.

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

• Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
• Unscrew the head from the battery compartment. Set the battery compartment aside.
• The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
• Reflector stays with the head. Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up and set it aside. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
• Reflector stays with the bezel. Set the head aside, LED side up. Using a strap wrench, unscrew the reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up and set it aside. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
• If the upper O-ring is not on the lens, carefully remove it from the bezel and set it aside. If the upper O-ring is on the lens, carefully pick it up and set it aside.
• Pick up the lens. If the lower O-ring sticks to the lens, remove it and carefully set it back on the reflector in the O-ring groove. Set the lens aside.
• Set the new lens centered over the reflector and lower O-ring. Verify the lower O-ring is seated in the O-ring groove.
• Place the upper O-ring on the lens directly above the lower O-ring.
• Carefully place the bezel over the stack and screw it down. Ensure that the O-rings sit in their little grooves and do not come out and get pinched. If the reflector stayed with the bezel during disassembly, lift the stack off the table keeping it in the same orientation and place it on the head and screw the reflector into the head. Tighten everything by grabbing the bezel and head. You only need to tighten until the gaps between the bezel, reflector and head are gone - do not over tighten.

This cut-away diagram is from the Details page and will assist you in understanding the procedure. The procedure is the same for all models.

• Do not touch the reflective surface of the reflector - the reflective surface cannot be cleaned - touching the reflective surface will damage it. Do not touch the LED - touching the LED will damage it.
• Unscrew the head from the battery compartment. Set the battery compartment aside.
• The reflector holds the bezel and head together. When you unscrew the bezel from the head, the reflector normally stays with the bezel. However, sometimes the reflector will stay with the head. The procedure changes depending on which circumstance happens.
• Reflector stays with the head.
  • Put the head on the table reflector up. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the head on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the head, reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • If the upper O-ring stayed with the bezel, gently remove the O-ring from the bezel and set it aside. If the upper O-ring stayed with the lens, carefully pick it up off of the lens and set it aside. Set the bezel aside.
  • Remove the lens from the stack and set it aside. Remove the lower O-ring from the stack and set it aside.
  • Use a strap wrench to remove the reflector. Set the old reflector aside. Leave the head sitting on the table LED side up.
• Reflector stays with the bezel.
  • Set the head aside, LED side up.
  • Using a strap wrench, unscrew reflector from the bezel until the O-ring is exposed and stop there - you should now be able to use your fingers to finish unscrewing the reflector. Put the bezel/reflector assembly bezel up on the table - i.e., it will be sitting on the flat end of the reflector. Tap the lens gently with your finger nail so it is sitting on the reflector. Keeping the reflector on the table, continue unscrewing the bezel, taping the lens every half turn or so. When the bezel is free, carefully lift it straight up. You should be left with the reflector, the lower O-ring, the glass lens and possibly the upper O-ring in the stack.
  • If the upper O-ring stayed with the bezel, gently remove the O-ring from the bezel and set it aside. If the upper O-ring stayed with the lens, carefully pick it up off of the lens and set it aside. Set the bezel aside.
  • Remove the lens from the stack and set it aside. Remove the lower O-ring from the stack and set it aside. Set the old reflector aside.
• Screw the new reflector into the head, reflector side up. Place the lower O-ring in the groove around the reflector. Set the glass lens on top of the lower O-ring. Set the upper O-ring on top of the lens directly over the lower O-ring. Carefully place the bezel over the stack and screw it down. Ensure that the O-rings sit in their little grooves and do not come out and get pinched. Tighten everything by grabbing the bezel and head. You only need to tighten until the gaps between the bezel, reflector and head are gone - do not over tighten.

NOTE: You cannot swap buttons on the rotary control - only on Clicky style switch caps. This procedure only applies to the newer Acme-thread battery compartments and the Rev 3 version of the older V-thread battery compartments. Older battery compartments do not have user-replaceable buttons. The procedure is the same for raised and flush buttons.

This cut-away diagram is from the Details page and will assist you in understanding the procedure.

• Unscrew the switch cap and set the rest of the flashlight aside.
• Using an appropriately sized coin or pin wrench, unscrew the button retainer.
• Remove the old button and insert the new button. Be sure the new button is centered in the switch cap.
• Apply a small amount of grease to the back side of the button retainer. This will ensure it can slide over the rubber button without grabbing the rubber.
• Screw in the button retainer until there is a hard stop - i.e., the button retainer bottoms. Do not over tighten the button retainer.
• Screw the switch cap back on the flashlight.

The universal pocket clip and lanyard attachment will fit all models of our flashlights. The universal pocket clip can be installed on the switch cap to allow bezel down carry of your flashlight. The universal pocket clip can be installed on the head to allow bezel up carry of your flashlight. With the bezel up orientation, the flashlight may be clipped to a hat for hands free use. Finally, a lanyard may be attached to the lanyard loop - the U bend in the clip.

Your universal pocket clip and lanyard attachment comes with a #0 Phillips screw driver, which is needed for installation.

Follow these steps to install your universal packet clip:

• Loosen all three screws. The two outer screws only need to be loosened half a turn. The center screw should be loosened so the head of the screw is at the same height as the two outer screws.
• Slide the ring over the flashlight. For bezel down orientation, the ring will be over the switch cap and the lanyard loop on the clip should be flush with the end of the switch cap. For bezel up orientation, the ring will be over the head.
• Hold the clip in position and tighten the two outer screws.
• Continuing to hold the clip in position, tighten the center screw. The clip should be completely snug.

The installation is now complete. You reverse the procedure to remove the universal pocket clip and lanyard attachment.

Note: the center screw is slightly longer than the outer two screws. If the wrong screw is in the wrong hole, the clip will remain loose even with the screws tight. The two shorter outside screws are 0-80 x 1/8” pan head Phillips. The longer center screw is a 0-80 x 5/32” pan head Phillips.

The Clicky-style pocket clip for the EDC Executive and EDC LE flashlights installs between the battery tube and the switch cap in a groove between the two items.

This cut-away diagram is from the Details page and will assist you in understanding the procedure.

Follow these steps to install your Clicky-style packet clip:

• Unscrew the switch cap and set the switch cap aside.
• If the external O-ring was installed, remove it and set it aside. The external O-ring was visible prior to removing the switch cap and is visibly narrower than the internal O-ring. The external O-ring is not used when the Clicky-style pocket clip is installed.
• Remove the internal O-Ring and set it aside. The internal O-ring sits in a groove just past the threads. It is visibly fatter and slightly smaller in diameter than the optional external O-ring. Be careful not to damage this O-ring because it seals the switch cap.
• Slide the pocket clip over the threads, past the groove and onto the narrow shelf just past the O-ring groove. You will need to hold the pocket clip in this position temporarily.
• Replace the interior O-ring into its groove between the pocket clip and the threads.
• Replace the switch cap. The switch cap can be tightened against the pocket clip to keep the pocket clip securely in one position.

The installation is now complete. You reverse the procedure to remove the Clicky-style pocket clip.

You may want to save the optional external O-ring if you later remove the pocket clip - to provide a nicer exterior appearance. However, the optional external O-ring is not necessary and may be thrown away.

When the Clicky pocket clip is not installed, there is a gap between the battery tube and the switch cap. The purpose of the external O-ring is to provide a nicer exterior appearance by filling in the gap. The external O-ring is optional and has no effect on the operation of the flashlight - it is not required.

The external O-ring is installed by rolling it over the Clicky switch cap and into the gap between the battery tube and the switch cap.

The groove width can be adjusted by loosening or tightening the Clicky switch cap slightly, and should be adjusted to be large enough to allow the O-ring to sit down into the groove so it is flush with the outside surface. This provides the best appearance and keeps the O-ring recessed so it will not snag on anything.

HDS Systems has designed and manufactured many LED flashlights over the years, starting with the Action Light headlamps. For complete information on our older models, please see our Legacy product information.

Flashlights manufactured from 2004 to 2008 were characterized by fine anodized V threads (32TPI). The Arc4 design used a switch located in the head even though the button was located on the back of the battery compartment. Thus there was no need for a switch signal wire in the battery compartment. Early versions of the EDC Ultimate and EDC Basic battery compartment used a dual U signal wire system to move the signal from the switch to the head. These lights are identified by a smooth, non-removable switch cap. Later versions of the EDC Ultimate and EDC Basic used a sleeve spring signal wire that slides into the battery compartment. These lights are identified by a knurled removable switch cap. The NovaTac and EDC Classic flashlight designs also used the sleeve spring signal wires.

Flashlights manufactured from 2009 to 2010 are characterized by medium bare metal V threads (24TPI) and serial numbers below 20,000. The Twisty models had two different battery compartments that differed only in the mechanical layout of the negative plug and lanyard attachment. The Clicky models had three different battery compartment designs. The first generation design used a knurled non-removable switch cap and can be identified by the 4 tiny holes at 90° intervals close to the battery tube - i.e., close to the edge where the switch cap meets the battery tube. Do not try to unscrew or otherwise disassemble the switch cap on a first generation battery compartment as you will damage it.

The switch cap on the second generation battery compartment unscrews and you will see two U shaped wires on the end of the battery compartment and a circuit board with a ring inside the switch cap. Although a pocket clip will fit into the gap between the switch cap and the battery compartment, the second generation battery compartment was not designed to accommodate pocket clips and the switch may stop functioning while a pocket clip is installed.

The switch cap on the third generation battery compartment unscrews and you will see a tactile dome switch on the end of the battery compartment and the button is retained in the switch cap by a threaded retaining ring - allowing the rubber button to be swapped.

Flashlights and accessories manufactured from 2011 onward are characterized by robust Acme threads and serial numbers from 20,000 onward.

All recent flashlights have a color ring on the positive contact to indicate the maximum calibrated lumen output. Legacy flashlights marked "Everyday Carry" on the bezel have no ring and are 120 lumens. Other Legacy flashlights without a color ring are 140 lumens. Finally, lights from the Twisty series used a color pen to mark the circuit board but that ink proved problematic in that grease or alcohol would remove the ink patch during cleaning. Non-white (monochromatic) lights do not have a ring because their output is not rated in lumens.

• Yellow - 100 lumens
• Green - 120 lumens
• White - High CRI 120 lumens
• Blue - 140 lumens
• Purple - 170 lumens
• Red - 200 lumens
• Orange - 250 lumens
• Yellow - 325 lumens

Over the years, we have upgraded our software to improve the utility and reliability of our flashlights. Below you will find the edit history for all versions of the software that can be upgraded to the current version - starting with release 1.22 in March of 2010. Only significant changes are listed. Earlier versions of the software require earlier versions of the hardware that are not compatible with the current software.

Your light will tell you what version of software it is running. To retrieve this information, you start by performing a factory reset but you do not release the button until the light begins flashing - roughly 10 seconds after the light turns off and roughly 20 seconds after you pressed the button. Note that since you are performing a factory reset, you will loose any customizations your have made and will need to make the customizations again. Here is the procedure to determine the software version number:

• Turn on your flashlight.
• Unscrew and open the battery compartment - your light will go out.
• Screw the battery compartment back onto the head. As you are doing this, the light will turn on dimly - this is the reset indication.
• Before the light turns off, press and hold the button. The light will become brighter when the button is pressed.
• After 10 seconds, the light will turn off. Do not release the button - continue holding the button down.
• After another 10 seconds, the light will begin to flash. You may now release the button.
• The flashes are grouped as 8 flashes with a pause separating them. Short flashes represent a 0 while longer flashes represent a 1. What you will be looking at are binary numbers. Write down the sequence of zeros and ones and use your favorite binary to decimal converter to convert the binary strings to decimal numbers.
• The numbers will continue to flash until you again unscrew and open the battery compartment.

If you are running 1.xx software, you will see a single number when the button is released and two numbers when the button is pressed. The two numbers are separated by a short pause and repeat after a longer pause. If you are running 2.xx software, the button is ignored and you will see three numbers separated by short pauses that repeat after a longer pause.

The single number displayed with the button up has no useful value and should be ignored. The same is true for the first of the three numbers for versions prior to 2.2. The first of the three numbers starting with version 2.2 is the calibrated output divided by 10 and rounded to an integer. As an example, a 325 lumen light will have the value of 33.

The two numbers displayed with the button down or the second and third of the three numbers is the version number. The first number will be either a 1 or 2 and is the major version number. The second number is the minor version number. Version numbers are normally formatted as <major>.<minor> - e.g., 2.18.

• 1.22 - released March 2010 - new power supply.
• 1.23 - released April 2010 - added ramp up/down when enabling/disabling features.
• 2.0 - released March 2011 - Rotary UI, burst enable option, burst moved to 40 seconds long, no button for version display. This software release corresponds with the release of Acme threads and serial numbers of 20,000 and above.
• 2.1 - released March 2011 - code cleanup.
• 2.2 - released March 2011 - calibration improvements, display calibrated lumen value with version numer.
• 2.3 - released June 2011 - end of battery handling (improved performance for dying batteries), lower idle current (increased run time).
• 2.4 - released September 2011 - end of battery handling, rotary control resets auto-off (any movement of rotary control will reset the auto-off function), double-blink below 50%.
• 2.5 - released September 2011 - double-blink below 50 lumens.
• 2.6 - released October 2011 - Clicky Tactical UI.
• 2.7 - released October 2011 - improve end of battery handling.
• 2.8 - released February 2012 - shorten locator flash.
• 2.9 - released March 2012 - ignore bad rotary codes instead of error code.
• 2.10 - released December 2013 - Rotary Tactical UI, calibration, internal cleanup, drop button lockout, locator flash enable option, rotary C & D presets to strobes, arbitrary exponent logarithmic spacing (always 24 levels), minimum to 0.02 lumens, flicker mode (undocumented, 5 clicks from off).
• 2.11 - released April 2014 - higher speed fast strobe per research studies, CCW in Tactical UI is rotary.
• 2.12 - released October 2014 - new configurations.
• 2.13 - released December 2014 - skipped because some think 13 is unlucky.
• 2.14 - released January 2015 - locator flash option controls quad-click, swap A/B for Tactical UI, triple-click from off latches level for Tactical UI, flicker to 7 clicks from off.
• 2.15 - released January 2015 - true momentary at 6 clicks from off, flicker to 9 clicks from off.
• 2.16 - released May 2015 - true momentary when Turn On option disabled.
• 2.17 - released May 2015 - support for L91 AA.
• 2.18 - released February 2018 - simplify default Rotary UI, level lock to triple-click from on for Tactical UI, return option and triple-click from off for button lockout, option to enable true momentary, bicycle strobes and configuration, improved auto-off.

Your flashlight was not designed to be modified after it has been assembled. To make your flashlight as reliable as possible, all connections are soldered together and all of the electronics have been potted. This seals the electronics and makes your flashlight very rugged. There is no safe or cost effective way to swap LEDs.

The LED board is thermally, electrically and mechanically joined to the power supply as well as the metal superstructure. Thus, there is no good way to remove the LED board or otherwise modify it. Getting the LED board hot enough to melt the solder holding the LED to the board requires getting the whole head to the melting point of solder, which takes a lot of time and a lot of heat and will easily exceed the thermal ratings on all of the parts in the power supply, not to mention the LED itself. A broken light is the typical result.

Many people have tried to replace the LED on their light and have destroyed the power supply in the process. If you break the power supply, it will cost you the current price of a head less the cost of the reflector assembly to replace it. Even skilled modders have paid for new power supplies. So don't try to modify your light.

The least expensive way to upgrade the LED in your flashlight is to sell your flashlight on the used market and then purchase a new one. Our lights retain their value even after they have been well used and so there is a thriving used market for our flashlights. This is a testament to how durable our flashlights are and how good our warranty service is.

Or consider gifting your old flashlight to a family member or one of your friends.

Your flashlight was not designed to be a dive light. However, if you take care to address certain issues, the light can be made to serve the purpose.

Only use Clicky models for this purpose - i.e., EDC Executive, EDC Bicycle and EDC LE configurations. These designs have very robust seals that are always used in a static fashion. Do not use rotary control models - i.e., EDC Rotary and EDC Tactical configurations - as it is very easy to dynamically load the seals at depth and cause them to leak.

The water pressure will eventually press the button - as if you were pressing it manually. Thus, it is necessary to configure the flashlight so the press-and-hold preset setting is the same as the turn on preset setting so water pressure activating the switch will have no unexpected effect. Note that once the water pressure has pressed the switch, it will not be possible to turn off your flashlight until you have surfaced.

If you get water inside the battery compartment - especially salt water - the battery voltage will power electrolysis and release an explosive mixture of hydrogen and oxygen gas. Electrolysis will also cause severe corrosion.

If water gets into the battery compartment, rinse the battery and the interior of the battery compartment with fresh water, shake out any visible water and allow to completely dry before reassembly.

Our emphases are on function, reliability and utility. Although we put considerable effort into making our products look nice, there are production issues that result in small surface blemishes that we generally consider part of a normal product. In other words, we are not making jewelry.

Knurling is a good example. Although we would love to have perfect knurling, creating knurled parts is as much of an art as it is a science. There are a large number of parameters that go into creating knurling and any one of those being off can cause various issues with the knurling. It is not cost effective to throw away all of the parts that have defects in the knurling just because of an aesthetic issue.

Part surface finish between different part runs is another place where you can find differences. One part may be slightly more shiny than the mating part. Or one part may have more visible machining marks. These issues are purely aesthetic and have no affect on the operation of the product.

Reflector surfaces are another place where tiny imperfections - typically bright spots or lines - may be visible when the light is turned on. These imperfections have no detectable influence in the beam pattern or the light output. After all, the light was calibrated using that very reflector.

LED centering is another issue that comes up. It is just not possible in production to get the LED perfectly centered every time. All assembly steps have positional tolerance and as long as the total position is within tolerance, there is no visible affect on the beam pattern or light output.

We make a judgement call about these things. On occasion, something gets missed that should have been caught. Sorry, it happens. If you think your product has a particularly egregious aesthetic defect, send us a photo and we will take a look. If we agree, we will be happy to take care of it under warranty.

Tail standing is not an advertised feature. The air-tight seal on the battery compartment can cause the flush button to bulge out when the air pressure inside the flashlight is higher than the outside air pressure. Changes in elevation, weather and temperature can affect the relative air pressure within the flashlight.

You can improve tail standing by equalizing the air pressure inside the flashlight. The easiest way to accomplish this is to loosen the switch cap until you can see the O-ring that is normally covered by the switch cap. The entire O-ring should be visible. Then, gently press the button and hold the button down while screwing the switch cap back down. You can release the button once the O-ring has been completely covered by the switch cap. The switch will probably activate while you are screwing down the switch cap - this is normal.

The same procedure can be done with the head - such as would happen when changing the battery. The newer battery compartments with the Acme threads have a vent hole that allows the passage of air until the O-ring seals. The older battery compartments with V-threads do not have the vent hole and will not produce the same results. This is because the head threads are usually coated with a generous amount of grease and that grease will seal the threads long before reaching the O-ring seal, thus trapping and compressing a large volume of air. The switch cap threads typically have a minimal amount of grease and so those threads will leak air until the O-ring is reached, minimizing the amount of trapped and compressed air.

HDS Systems designs and builds its flashlights in Tucson, Arizona from parts that come from all over the world. We prefer using American parts whenever practical, but sometimes it is just not possible. As we build leading edge flashlights, we must have top-of-the-line parts to make our designs work. Let's take a look at a few examples.

Cree currently makes the best cool-white single-die emitters (LEDs) available. The wafers (i.e., the dies) - the heart and sole of the LED and the part that converts electricity into light - are manufactured in the USA. However, Cree sends the wafers to a foreign country to be packaged into LED emitters and put on reels. So when the reels of LEDs come back to the USA, they are now considered to be of foreign origin.

Nichia currently makes the best high CRI single-die emitters (LEDs) available. They are manufactured in Japan.

The CPUs we use are made in the USA but packaged in a foreign country. The packaging process changes the CPUs from American made into foreign made.

Major electronic components mostly come from overseas because the top quality components needed for our designs are not made in the USA.

All of the design, testing and assembly work is done in the United States. And our machined parts are manufactured in the USA. So the overwhelming majority of value in each flashlight comes from the United States.

In order to claim "Made in the USA", the Federal Trade Commission (FTC) says a product must be "all or virtually all" made in the United States. They define the phrase "all or virtually all" to mean that all significant parts and processing in a product originates in the United States. We consider the LED and other major electronic components to be significant components.

We think we are disqualified from making the "Made in the USA" claim for our flashlights because the LED and major electronic components are not "Made in the USA". We prefer to error on the side of not making the claim rather than making an inappropriate or misleading claim of "Made in the USA". We think this is in the spirit of the FTC "all or virtually all" rule.

Although we do not claim "Made in the USA", our products comply with the Buy American Act and are "Built in the USA".

The European Union (EU) has a body of standards and regulations for safety, interference and environmental considerations. The three primary standards of interest are CE, RoHS and WEEE.

CE is similar to the Underwriters Laboratory's UL rating and the FCC's interference standards. To receive the certification you submit your product to a certification laboratory to be tested. Our flashlights have passed CE testing and are CE certified.

RoHS stands for Restriction of Hazardous Substances Directive. This directive has to do with the removal of certain "hazardous" materials from newly manufactured equipment. Lead - which typically makes up 37% of solder - is one of the listed materials. As of July 2006, EU law forbids the importation of non-compliant products unless imported under one of the many exemptions.

The problem with RoHS is that it legislated changes in the manufacturing process prior to there being a demonstrated reliable alternative process. RoHS compliance currently requires the use of brittle no-lead solders, more difficult to solder surfaces and higher processing temperatures. These three things have detrimental effects on the reliability of all products. Further, many RoHS surfaces incorporate a tin coating, which can grow tin whiskers, producing short circuits months or years after the product was built.

It is interesting to note the list of equipment exempt from RoHS: military, national security, medical, aviation, monitoring and control and transportation vehicles. What do all of these exemptions have in common? Reliability. Suffice it to say we will not be RoHS-compliant until we can build reliable products with RoHS-compliment methods. In the mean time, you can purchase our products under one of the listed exemptions.

WEEE stands for Waste Electrical and Electronic Equipment Directive. This directive requires that the "producer" collect, treat, recover and recycle old products rather than dispose of these old products in land-fills. This directive generally became effective August 13, 2005.

In order to comply with this directive the "producer" is required to take financial responsibility for processing end-of-life products. In this case, the EU importer is considered the "producer" and thus must make provisions for assessing customers and administering any required fees to take care of disposal using an EU-qualified disposal method. There are exemptions for military, national security and other types of equipment.