Ra Lights F.A.Q.

Please review the following frequently asked questions, the User's Guide for each product and the product comparison chart.  If you have a question after reviewing this material, please contact us by e-mail or phone.

What is an LED?

There are many types of devices that generate and emit light and these devices are usually classified as being incandescent, arc and solid state.  The Light Emitting Diode (LED) is a solid state device.  The LED is a rugged device that can emit light with high efficiency.  Let's compare this to the other types of devices.

The common incandescent light works by passing a current through a fine wire - the filament - to raise the temperature of 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.  The glass bulb is also relatively delicate and can break if exposed to a significant shock.  Finally, the incandescent light is relatively inefficient with typical efficiencies in the 15 to 22 lumens per watt range.

The common florescent 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 to white light.  These lights can generate light that looks very close to noon day sunlight.  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 glued or soldered 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 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 without damage.  The latest LEDs are now exceeding 90 lumens per watt at medium power levels (mid 2009) and can be expected to increase in efficiency by roughly 20 to 25% each year for the next many years.

Almost all white LEDs manufactured today 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.

What are Lumens, LED Lumens and Touch Lumens?

The lumen is the international unit for measuring the quantity of light relative to the sensitivity of your eyes per unit of time from a light source.  The spectral content of the 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 deep red light (675nm).   The lumen does not address how the light may be concentrated by a reflector or lens, nor does it address how brightly a surface will be illuminated at some distance.  The lumen simply measures the total amount of eye-sensitive light being emitted by 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 the 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 data sheet - without taking any losses into consideration.  Or they may say "up to" and list the maximum bin lumens.  This is often referred to as LED lumens or specification sheet lumens.

It should be pointed out that the LED's lumens are measured under ideal conditions - 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 may loose 20% or more of it's 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.  To make matters worse, typically less than 75% of those lumens will make it out the front lens due to losses in the reflector, lens and internal absorption.  In the end, you may be getting 35 to 45% of the claimed lumens out the front of the flashlight.

A better way to rate a flashlight is to measure the light from a typical LED after it has passed through the lens. This is sometimes referred to as torch (flashlight) lumens or out-the-front (OTF) lumens.  Further, the better flashlight manufacturers will use the lowest output LEDs during those measurements so all flashlights will produce at least the number of lumens stated - and most will produce more.

We go the final step and measure the output of each flashlight after it is completely assembled and adjust 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 the flashlight's true lumen output can be measured and adjusted under representative operating conditions.

What are lumen-minutes?

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 end point is usually after the initial output falls to something convenient such as 50% or 25%.  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 20% or a decrease of 17% 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 light output when the light output cannot be dramatically changed because the eye will rapidly adapt to the existing light output in both directions and any small difference in light output will be muted.

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 is 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.

What is a color rendering index (CRI)?

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. The maximum possible CRI is 100.

A typical cool white LED has a CRI around 72. Most warm white LEDs have a CRI around 83. Our high CRI warm white LEDs have a CRI of 93 - the highest in the industry. 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.

Why are warm-white LEDs less efficient than cool-white LEDs?

All light sources convert electricity to visible and invisible light. However, only the visible part of the light helps us see. The visible part of the spectrum is measured in lumens.

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 eye. So most of the cool-white spectrum adds to the lumen value.

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 eye. 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 efficiency of the LED.

What is the practical difference between 100, 120, 140 and 170 lumen output?

Your eyes respond to light in a logarithmic way. As such, small differences in light output cannot be seen. It generally takes a 40% increase in light output for you to notice a small (slight) increase in light output - the difference between 100 and 140 lumens or 120 and 170 lumens. The average person will not notice a 20% increase in light output. This is the difference between 100 and 120 lumens, 120 and 140 lumens or 140 and 170 lumens.

Beam pattern can have a significant effect on the apparent brightness of a flashlight when comparing two flashlight 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 but wider throw.

The differences in LED efficiency can have a significant affect on runtime. In general, the amount of power needed to generate the maximum output is the same in all cases. The higher light output is the result of higher LED efficiencies. The maximum power setting is typically less than half as efficient as the next lower setting. This is due to pushing the battery, power supply and LED past their optimum points in order to achieve the maximum light output. In contrast, the lower power setting are operating in their most efficient ranges. Thus, a 170 lumen flashlight running at the 120 lumen level will get over twice the runtime compared to a 120 lumen flashlight running at full power.

What is burst?

Burst allows you to see the maximum distance without sacrificing excessive battery life. As a result, you can use burst to see much further that you would ordinarily be able to see. To understand how this works, we need to explain some background material.

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 the 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 the light - effectively becoming more efficient at gathering the available light. Thus, you want to use an appropriate amount of light for what you are normally doing without over illuminating the scene.

The second thing to understand is that your flashlight is much less efficient when producing the absolute maximum output than if it is when 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, you want to limit the amount of time you spend using the absolute maximum output. Burst takes care of this automatically for you. Although there is just a slight visual difference between the maximum output and the next level down, the difference in battery life is huge.

The next thing to understand is the Inverse Square Law - it takes 4 times as much light to see twice as far - all else being equal. Given a 41% increase in output between adjacent brightness levels, it takes 4 brightness levels to see twice as far. Thus you can increase the output by one level and see 19% further, two levels and see 41% further, 3 levels and see 68% further or 4 levels to see 100% further.

The last thing to understand is how long you need extra light for. You need the extra light long enough to make a positive identification. 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 firing your weapon within a few seconds. Thus, you only need absolute maximum for a relatively short period.

So let's take two scenarios to illustrate the best use of your flashlight while navigating at night. In the first scenario, you turn your light onto the High setting and take off. After 10 seconds, your flashlight will automatically step the light down from the absolute maximum to one setting lower to maximize runtime without making a significant visual difference. Many people do not even notice the drop under normal conditions of use. As you are walking along, you hear a noise in front of you but you cannot see what made the noise. Pressing the button will reactive the absolute maximum output allowing you to see 19% further than without it.

For the second scenario, we will assume you use the Low setting to take your walk. If you point the light one or two body lengths in front of you, you have plenty of light to see with. Again, you hear the noise, point the light at the noise and push the button. But this time, you can see 22.5 times as far as you can see before pushing the button. That certainly sounds impressive but can you really see further?

The answer is yes - by a fair 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 a bright light, it is difficult to avoid over lighting the scene and ruining your dark adaptation. With a dim light, it is easy to build your dark adaptation, which counts as a couple of additional brightness levels when you turn on the high output setting. Two additional brightness settings allow you to see 41% further. Three brightness settings allow you to see 68% further. That is a lot of extra reach.

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

How far can I see with my light?

There is no industry standard for measuring the distance you can see with a light.  In order to measure the distance you can see, you have to define the surface illumination and the surface area to be illuminated.  Let me explain.

A flashlight beam emits a certain amount of light.  That light travels some distance between the flashlight and the object you are trying to illuminate.  As the light gets further from the flashlight, its ability to illuminate the object decreases by the inverse square of the distance.  That is, if you move the object twice as far away the surface brightness (luminous intensity) will decrease to 25% of the original surface brightness.  But at the same time, the flashlight will illuminate 4 times the surface area.  Or if you move the object 10 times as far away the surface brightness will decrease to 1% of the original surface brightness while illuminating 100 times the surface area.  This is known as the Inverse Square Law of light.  As you can see, you have taken the same amount of light and spread it over a larger surface area with a corresponding decrease in surface brightness.

Let's say your flashlight can illuminate a surface to 1500 lux at one meter.  At 10 meters (33 feet) you can illuminate the surface to 15 lux.  If you pick 2.5 lux as the required brightness, you can see 25 meters (80 feet).  If you pick 1 lux as the required brightness, you can see 39 meters (127 feet).  If you pick 0.1 lux - the brightness of full moon light - as the required brightness, you can see 122 meters (402 feet).  The practical limit on distance is controlled by the amount of light available, your level of dark adaptation, beam pattern and other factors.

How can you apply this in a practical way?  Let's assume your eyes have adapted to a low brightness beam while taking a walk with the beam pointed a few body lengths in front of you.  You hear a twig snap in the distance - is it friend or foe?  You point your light into the distance but the inverse square law effectively "dims" the light - making it difficult or impossible to see the distant object.  Switch to the high setting and suddenly the distant object is well illuminated.  After you have identified the distant object, switch back to the lower setting and go back to your walk.  During this process 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 adaptation, you have increased the effective range of your flashlight.

Which beam pattern is best?

There is no one "best" beam pattern.  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 with the same surface brightness but we can see four times the area with the same brightness at the closer distance.

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.

Why do you regulate power to the LED?

Power regulation maintains a consistent amount of power to the LED and hence keeps the light output constant as the battery is used and the temperature changes.  HDS Systems is the only company in the world to use a constant power regulation method to drive LEDs - we invented it.  Our regulation circuit - also called a power supply - converts the battery voltage to the precise voltage required by the LED to keep the power constant.

The sophistication 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 simplest or least expensive circuits tend to do a poor job of regulation and/or are inefficient.  More sophisticated circuits such as switching current regulator do a better job.  However, our switching power regulation circuits do the best job of keeping the brightness constant and are the most efficient, but tend to be more expensive.

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 circuit or a pure 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 notification and time to find a safe place to change batteries.

What is visually even brightness spacing?

Your eyes respond to light in a logarithmic way.  That means that a significant perceived increase in brightness requires a doubling in the amount of light.  Photographers refer to this change as one f-stop.  As an example, to increase the brightness 4 full shades of brightness requires 16 times the amount of light.  The brightness levels on your light are spaced to provide small, visually even changes in brightness.

How does this affect battery runtimes?  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 minimum brightness level compatible with the task you are performing. The lowest brightness setting will help preserve your night vision adaptation without using a red filter.

Why are your lights calibrated?

The efficiency of LEDs 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 seen when two flashlights are compared side-by-side and customers complain that the dimmer light is defective.

We have chosen to calibrate (adjust) each flashlight to a specified output and to guarantee a minimum runtime.  This results in consistent light output from one flashlight to the next.  And the typical flashlight will run for 25% longer than the advertised minimum runtime prior to the first stepdown.

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.

Why do battery runtimes vary?

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 and allow the input power to vary.  This results in constant light output but causes variations in the battery runtime from one flashlight to the next.  We guarantee a minimum battery runtime at the rated light output.  Typical runtimes will be 25% higher than the minimum runtime.

The type of battery used will have an impact on battery runtime.  The most significant difference in batteries is how they handle the highest power levels.  You should always choose batteries that can handle high continuous currents.  Alkaline batteries are a poor choice in this type of application.  Lithium and nickel metal hydride are the preferred battery chemistries for high power applications.

Temperature can also have a significant impact on battery runtime.   As the battery temperature drops towards and below freezing, the performance of the battery will deteriorate.  How much power is lost with temperature depends on the battery chemistry and construction.  Lithium is the preferred battery chemistry for cold environments.

LEDs and batteries are significantly less efficient at higher power levels.  Therefore, the highest brightness levels consume disproportionately larger amounts of power and thus battery life drops at a faster rate than expected.

What are the differences between primary and rechargeable lithium batteries?

The main difference between primary and rechargeable batteries is that primary batteries are used once and thrown away while rechargeable 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 $2.00 for primary batteries and $36.00 for two rechargeable batteries and the charger, the break even point is 18 battery changes.

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

At the highest power settings, the absolute capacity of a primary battery is similar to the capacity of a rechargeable battery. This is due to the high internal losses in the primary battery and the low internal losses of the rechargeable battery under high current conditions.

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

Why must rechargeable batteries be treated special?

Rechargeable batteries can be damaged by over-charge, over-discharge or reverse charging so these conditions must be prevented. Lithium-ion (Li-ion) batteries are electrically delicate and special precautions must be taken to ensure safe use of these batteries. When used within their design limits, Li-ion batteries are both safe and inexpensive over the long term and we recommend their use with our products.

There are several different kinds of Li-ion batteries with the primary distinction being the charge and nominal voltages. For the purposes of this discussion, we are only interested in the higher voltage chemistries - with a charge voltage of 4.2V and a nominal voltage of 3.6V - 3.7V. Do not use any other kind of Li-ion battery with our products.

Li-ion batteries are sensitive to temperature. They may be used from -20°C (-4°F) to 45°C (113°F). However, they should be brought close to room temperature when recharging - from 15°C (59°F) to 35°C (95°F).

Over-charging is caused when a charger does not properly regulate the charge voltage or current. Many (most) chargers continue charging to the high side of 4.2V and do not cut off after charging is complete. This will damage the battery over time and reduce the number of charge cycles to less than 100 full charge cycles.

A good quality charger will either cut off the charging power when the battery reaches full power or will use a voltage that is slightly lower than the maximum value. If a lower voltage is used, such as 4.1V, the battery can be left charging for an extended period without damage to the battery. When properly charged, a battery will accommodate 500 or more recharge cycles over a multi-year period.

Over-discharge takes place when the cell voltage is allowed to drop below a specified minimum voltage. For Li-ion batteries, this is around 2.7V. However, most of the charge has been removed by the time the battery reaches 3.0V. Any device that uses Li-ion batteries must be built to specifically recognize a Li-ion battery and to warn the user prior to reaching these limits. If the user does not heed the warning, the device must turn off to prevent over discharge.

Most quality Li-ion batteries sold today contain a protection circuit to prevent over-discharge. When the protection circuit detects an over-discharge, it turns off the battery. This effectively causes the sudden failure of the device containing the battery. Our flashlights identify and properly handle Li-ion batteries and prevent this sudden failure.

It would be dangerous to simply turn off the flashlight unexpectedly to prevent over-discharge. Instead, the output brightness is reduced, which has the effect of raising the battery voltage slightly. Every time the battery voltage drops, the output brightness is again reduced to maintain the battery voltage above the safe level. 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 help. Your light will continue blinking for an unspecified amount of time before the voltage reaches a critical level for the battery and the light turns off to preserve the battery.

Reverse charging takes place when you have several batteries in series and one of the batteries is weak.  The weak battery is over-discharged and then driven into reverse charge by the stronger batteries.  The mechanism discussed above effectively prevents reverse charging.  So does using a single battery.

What are the differences between R17670, 18650 and R19670 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 a R17670 battery will be 17mm in diameter and 67.0mm long.

A R17670 battery has more than double the capacity of a recharge CR123 size battery (R17345) and will provide over twice the runtime compared to the smaller battery.

Most manufactures advertise both bare 18650 cells and protected R19670 batteries as being 18650 batteries for historic reasons. When 18670 cells first came out many years ago, they were only available in the unprotected format so the 18650 size designation was correct. But over time, protection circuits were added to the 18650 cell for safety reasons. Adding the protection circuit increased the size of the resulting battery to 19670. Hence the proper size designation for a protected 18650 cell is 19670. But because these protected batteries were built around the original 18650 cells, most of the suppliers continued to use the older incorrect 18650 designation instead of the newer correct 19670 designation. This has proven to be very confusing to many customers.

A R17670 battery has roughly 70% of the capacity of the standard capacity R19670 (18650). In most applications, this will not have a significant impact on the utility of your flashlight. For most applications, you will find the R17670 will last a full shift. And for those marginal cases, carrying a second battery will provide ample runtimes.

How long will the LED last?

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.  Your flashlight uses a sophisticated regulation technique to manage the heat and current in your flashlight to protect the LED from catastrophic failure and to prevent premature aging.  Premature aging slowly reduces the light output of the LED.

Are all white LEDs the same color?

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 exact resulting tint can vary significantly because of variations in 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 color.  From the aesthetics point of view, this can be annoying.  If you compare two lights side by side they are bound to appear two different shades of white - which always leads to the question of which is whiter?  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.

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.

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 5000°K to 7000°K with typical noon daylight being in the range of 5500°K to 6500°K.  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 guaranteed tint LEDs have a typical correlated color temperature in the range of 5700°K to 6300°K and lie close to the Planckian black body radiator line. The high CRI LEDs have a more complete spectral content and are better at rendering colors but are lower in color temperature than the regular cool-white LEDs.

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.

What is tint control?

The typical way to dim an LED is by reducing current flow. However, as the current is reduced, the tint of the LED can shift toward the green part of the spectrum.  The other common way to reduce brightness is to turn the LED on and off very rapidly - often referred to as PWM (Pulse Width Modulation) or PFM (Pulse Frequency Modulation).  However, PWM can generate an annoying flickering sort of like a disco strobe and results in a lower overall system efficiency.  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.

Do you overdrive your LEDs?

No, we do not overdrive our LEDs.  Overdriving an LED produces excessive heat, reduces the efficiency of the LED, 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.

Our advanced technology allows our lights to provide superior light output and battery run times without overdriving our LEDs.

Can I use my flashlight as a dive light?

We do not recommend you use your flashlight as a dive light.  The rotary seals are not designed to seal when in motion and the water pressure will eventually press the clicky button - as if you were pressing it manually. However, you can 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 affect.

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 corrosion.

If water gets into the battery compartment, rinse the battery and the interior of the battery compartment with fresh water and dry.

What is military Type 3 hard anodize?

Anodize is a layer of oxidation formed on the surface of 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. 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 almost black.

Type 3 anodize can vary in color from a medium gray to a dark olive. 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.

What is aluminum titanium nitride (AlTiN)?

AlTiN is an acronym for Aluminum Titanium Nitride. AlTiN is a dark colored vapor deposition coating that is applied in a vacuum. AlTiN is so tough and hard it is used to coat machine tools, drill bits and other wear surfaces to make them last longer. In addition to wearing better than hardened steel, AlTiN imparts a beautiful purple-black color to the surface it is applied to.

We use AlTiN to provide a dark non-glossy coating to our stainless steel bezels. We have found that this coating will easily out wear a military Type 3 hard anodize.

What is an anti-reflective (AR) coating on the lens?

The purpose of a lens is to transmit as much light as possible. As the light passes though an untreated air/lens surface, 4% 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 8% of the light can be lost.

An anti-reflective coating can be applied to the lens surfaces to reduce the amount of reflected light and thus increase the amount of light transmitted through the lens. Both surfaces should be coated to maximize the amount of light the lens can transmit.

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 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.

How do I install the pocket clip?

The pocket clip installs between the battery compartment and the switch cap in a special groove between the two items. Your flashlight is shipped without the pocket clip installed. Instead, an external O-ring has been placed in the groove for a nicer appearance.

Follow these steps to install your packet clip:

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

What is the purpose of the external switch cap O-ring?

There is an external groove between the switch cap and the battery compartment that will accept a bezel down pocket clip. When the pocket clip is not installed, a thin O-ring may be placed in the groove to improve the exterior appearance. The external O-ring has no affect on the operation of the flashlight and is not required.

The groove width can be adjusted by loosening or tightening the 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.

Why does the flush button not tail stand?

Tail standing is not an advertised feature. And 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 done with the head - such as would happen when changing the battery - 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.

Where are your flashlights made?

HDS Systems builds its flashlights in Tucson, Arizona from parts that come from all over the world, including the United States. As we build leading edge flashlights, we must have top-of-the-line parts to make our designs work. For example, we use two different types of LEDs because they are the best available - one comes from the orient and the other comes from Europe. We cannot buy equivalent parts made in the USA. The other electronic components mostly come from Asian countries. Again, for the significant parts such as the CPU, power transistors and power capacitors, we cannot buy equivalent parts made in the USA. However, all of the design, testing and assembly work is done in the United States.

In order to claim "Made in the USA", the 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 originate in the United States. We consider the LED and the CPU to be significant components.

We think there is sufficient foreign content to disqualify us from making the "Made in the USA" claim. 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".

What are CE, RoHS and WEEE?

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 affects 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 cannot be compromised.  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 becomes affective 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.