Frequently Asked Questions
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 and 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. 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 20 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 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 relatively rugged device that can withstand significant shock without damage. The latest LEDs are now exceeding 65 lumens per watt at medium power levels (late 2007) and can be expected to increase in efficiency by roughly 20 to 25% each year for the next many years. What are Lumens, LED Lumens and Touch Lumens?The lumen is the international unit for measuring the quantity of light per unit of time from a light source. For instance, your average inexpensive 100 watt incandescent light bulb generates 1700 lumens and those lumens escape from the light bulb in all directions. 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. The lumen simply measures the total amount of light being emitted by the source.LEDs are tested after manufacture and sorted into bins. One of the bin catagories 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 67.2 lumens to 87.4 lumens at 350mA into their T bin. Likewise, the LEDs that generate from 87.4 lumens to 113.6 lumens go into their U bin. Add to this a production tolerance of typically +/-10% for the manufacturer's measuring equipment and there is a fairly large range of output possible in any one bin. 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. This is ofter referred to as LED lumens. But the LED manufacturer is measuring the LED under ideal conditions - before the LED has had 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. And if the LED was from the bottom of the bin you may find the LED under real conditions is generating less than 60% of the claimed lumens. To make matters worse, typically less than 80% of those lumens will make it out the front lens due to losses in the reflector, lens and internal absorption. In the end you are lucky if you get 50% of the stated lumens out the front of the flashlight. The better flashlight manufacturers measure the light after it has passed through the lens - and is sometimes referred to as torch (flashlight) lumens. Further, they 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 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 is the practical difference between 70, 100 and 120 lumens output?The practical difference between a 70 lumen light and a 100 lumen light is a 19% difference in beam throw - all other things such as beam pattern being equal. In other words, you can see 19% further with the 100 lumen light. Even though the difference represents a 42% increase in light, your eyes respond to light in a logarithmic fashion and thus a 42% increase in light is roughly the smallest increase in light output that your eyes can easily distinguish.The difference between 100 lumens and 120 lumens is only a 20% increase in light output. Although 20% sounds like a lot, the difference is nearly indistinguishable to your eyes. However, increasing the light output by 20 lumens will take a dramatic toll on runtime because the battery, electronics and the LED all loose efficiency very quickly when driven to their maximum. As a result the last 20% increase in light output - which is almost invisible to your eyes - may cost you 50% of your runtime. Why pay such a penalty when you cannot easily see the difference? 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 looser's game to maximize output at any cost. Comparing the lumen-minutes will quickly show the folly. 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 your level of dark adaption, 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 many times. 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 is power to the LED regulated?Power regulation maintains a consistent amount of power to the LED and hence keeps the light output constant as the battery is used. The 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 or switching power regulation circuits can do a very good job of keeping the brightness constant and can be quite 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. There is a third type of switching power supply circuit used by Ra Lights 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 within 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 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 the lights calibrated?The efficiency of LEDs vary from one LED to the next. That means for a certain amount of input power the light output varies or for a certain light output the input power varies. 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.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.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. Why are rechargeable batteries treated special?Rechargeable batteries can be damaged by over-discharge or reverse charging so both conditions must be prevented. Over-discharge takes place when the cell voltage is allowed to drop below a specified level as the battery is used. The voltage below which the battery cannot safely discharge is mostly determined by battery chemistry. To prevent over-discharge, the battery chemistry must be recognized and the battery voltage must be carefully monitored.It would be dangerous to simply turn off the flashlight 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. Obviously, this cannot go on forever. When the lowest brightness is reached, it is assumed you have an emergency - i.e., you cannot change batteries and you still need light. At this point, we sacrifice the batteries to save your life. 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. 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?No. 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 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 three colors provide a 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. As you raise the temperature of the black body radiator, the color shifts from red toward 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 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. Ra Lights uses 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. Although the flashlight may be waterproof to the required depth, the switch mechanism is not designed for reliable operation at depth.If you get water inside the battery compartment - especially salt water - the battery voltage will power electrolysis and the release of 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 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 laboratory to be tested along with the testing fees. In some cases you may be able to reduce to total certification cost by performing and documenting the testing yourself with the option that a certified lab can monitor the testing. Our products are not currently 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. The problem with RoHS is that it legislated changes in the manufacturing process prior to there being a demonstrated alternative process. Thus far, none of our vendors have been able to demonstrate an alternative that can consistently create a finished product with similar reliability as our existing products. The alternative processes require higher temperatures and can have problems with yields, part degradation, embrittlement and tin whiskers. It is interesting to note the list of equipment exempt from RoHS: military, national security, medical, aviation, monitoring and control, transportation vehicles and stationary large scale industrial tools. 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 are satisfied that the problems have been solved. In the mean time, you may be able to 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.
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