Flashlight Facts

I. Lights and Lanterns

Picking the Right Light

What type of trips do you plan and how many batteries should you pack? Hikers may opt for one of our many lightweight, compact headlamps or flashlights, plus a candle lantern for camp. Rechargeable lights are budget and earth-friendly options.

Mountaineering and caving require bright, tough headlamps. Temps below 20F drain alkaline batteries fast so keeping the battery packs under clothing can help prevent this. Lithium batteries, on the other hand, excel in the cold but they are quite expensive.

For foreign trips, replacement bulbs and batteries are a concern. LED models are good because replacement LEDs are rarely needed. Models with long battery lives, common battery type or those able to be recharged are your best bet. Packing spare bulbs and batteries is also an option.

For car camping or emergency home lighting, various models of lanterns are widely available and work best.

Quick Tips
  • Always bring a dependable light source: LED lights are about the most reliable option.
  • LED lights are extraordinarily energy efficient. Some lights have both LED and bulbs, offering the best of both beams.
  • Always pack along spare batteries or fuel and bulbs for models that require them.
  • Keep a light or lantern and batteries or fuel in all your emergency preparedness kits.

II. Light Components


The material that comprises the body of the flashlight is an important consideration. The two common materials used for flashlight bodies are aluminum and plastic/polymer. The better lights tend to be made from aluminum but, depending on the grade of the plastic/polymer (and there are many), you may find high-quality lights with plastic/polymer bodies as well.

The most common example of an aluminum body is the Mag series of lights. An aluminum body is durable and although subject to deformation by sharp impacts, it can usually take a beating. Most aluminum lights are built in a cylindrical shape since that shape is the easiest to make when machining aluminum. When looking at light with aluminum bodies, consider the finish. The three primary finishes are discussed below.

  • Powder coat is considered the weakest finish. This type of coating I created by bonding paint to the metal using heat. It is corrosion-resistant but can be scraped off, in some cases quite easily.
  • Anodizing Type 2 is the next strongest finish. This finish is achieved by an electro-chemical process that forms a layer of oxidization on the surface of the metal that is then chemically colored. You will find this type of finish on most Mag lights. A wide variety of colors can be produced by anodizing. The finish may wear off and ding, but it holds up pretty under moderate to heavy use.
  • Anodizing Type 3 is the hardest finish available for aluminum. The basic process is the same as Type 2 (above) but the finish is very, very hard. Type 3 will take some serious punishment and will often wear away other metals before it shows any damage itself.

Lights made with plastic or polymer tend to come in a greater variety of shapes since plastic can be molded to virtually any shape desired. Plastic and polymers come in such a wide range of grades and types, we will not elaborate here. As a rule of thumb, the more expensive lights are made of better quality grades of polymers. A polymer body has some definite advantages over aluminum. Because the color mixed into the plastic itself, nicks and scrapes don't show up as easily as on aluminum lights. Polymer lights are naturally resilient and tend to flex instead of bending or denting when impacted. The wide range of colors available, allow you to choose your light for discretion or high-visibility depending on the task. For many purposes, a bright colored body makes the light easy to identify and spot against the background. This is especially important when hiking, backpacking or camping.


The purpose of the lens is to protect the bulb and reflector from impact and the environment. The lens may also be shaped or textured to change the beam of light that comes from the reflector.

Commonly a flashlight lens is plastic, but they can be made from a variety of materials. Plastic lenses of course, are subject to melting in high heat whereas a polycarbonate lens will not shatter and is temperature resistant. Other lights may use glass of various sorts, including Pyrex. Glass lenses are usually found in high-output flashlights that produce a lot of heat. A prismatic collimator lens focuses the dispersed light (emitted by the LED) into a tight beam. A sapphire coating on a lens helps cut down on glare.


The design of the reflector makes a difference in the way the light beam is emitted by the flashlight. Without a reflector, the light would spread in all directions, like a candle. There are several different types of reflectors, each with their advantages. Here are a few:

Smooth Reflector

The smooth reflector is the most common type used in your average flashlights. The beam put out by this type of reflector is usually full of "rings and holes" meaning rings of bright light and patches of darkness. Some of the better smooth reflectors put out a decent beam of light, but most do not. If the reflector is adjustable for focus, you can usually project a very sharp, tight beam a long distance, but once you try to spread the beam out for area lighting, you get the "rings and holes" again.

Course Faceted Reflector

In a course faceted reflector, the facets all act like little tiny mirrors, sending the spot of light in the same direction. This usually results in a very nice, smooth beam which does not need focusing.

Fine Faceted Reflector

In a fine faceted reflector, the facets are much finer than that of the course faceted reflector. The finer the facets, the smoother the beam.

Spiral Faceted Reflector

The facets of a spiral faceted reflector have the same effect as the faceted reflectors, above, but the fine facets in a tight spiral help it achieve a smoother beam.

Hybrid Reflector

The hybrid reflector contains faceting, but only near the bulb. This helps get rid of the central "hole" found in the beam from most smooth reflectors. It's a way to produce a decent beam without the expense of making the reflectors fully faceted.

Textured Reflector

This last one is called many things, including "textured", "orange peel" and "stochastic". This is considered by some to be the ultimate faceted reflector. Instead of facets, there is a gentle texture on the reflector that again projects a very smooth beam with little or no "rings and holes". This type of reflector is usually found in better quality lights.

Beam Type

An adjustable-beam light lets you match beam size to task, as opposed to a non-adjustable fixed beam. A third type, the focused beam, is essentially an LED with a lens that projects the beam in a way that increases its brightness, making the light emission more comparable to an incandescent bulb. All LED beams provide edge-to-edge consistency with no dead spots, rings, or holes.

If a faceted reflector is focused out, the facets disperse the beam so that the "rings and holes" are not as obvious as those created by a smooth reflector. If focused to a tight beam, the facets scatter only some of the light, meaning you will never achieve the same tight beam you could get with a smooth reflector.

LED, the Bulb That Wont Quit

LEDs will drain a battery three to five times slower than ordinary incandescent bulbs, making them more environmentally friendly (less battery waste). LEDs can run 100,000 hours (11 years) continuously before replacement, while a bulb can burn out in less than 40 hours. LEDs don't "blow" like a regular bulb and there is no glass or filament to break so LEDs are ideal for rugged use. The white LEDs produce a much whiter light than an incandescent bulb, which produces a somewhat yellow light. As the battery life is depleted, the LED will continue to produce a white light that dims gradually, whereas, an incandescent bulb will grow more and more yellow as the battery drains.

The two big drawbacks of an LED are: Cost and lesser degree of brightness when compared to incandescent bulbs. You will need many more LEDs to produce the same amount of light emitted from fewer incandescent bulbs. LEDs also burn much hotter, creating the need for heat sinks or ventilation to cool them.

Luxeon is a company that manufactures the Luxeon Star LED, which is one of the brightest LEDs currently on the market. Luxeon Star LED comes in a varying degrees of brightness depending. The maximum output of a 1Watt Luxeon Star is only 18 Lumens. You may get it 1-5% brighter by increasing the current, but this can easily damage the LED. Luxeon sorts out the best LEDs and sell them at prices that vary with quality grade, as the Luxeons are still plagued by QC problems. A premium 5Watt Luxeon Star LED is 120 lumens and cost almost $60. One of the biggest problems with the 5 watt LED is that it heats up really fast. A good 5Watt Luxeon Star flashlight will have a really good and massive Aluminum heat sink.

Heat Sinks

LEDs are generally the most efficient type of light, and don't usually generate as much heat as incandescent bulbs. The 5Watt and 1Watt Luxeon LED (with 4.5volts direct overdrive) generate a lot of heat. This is a normal side effect. They are efficient, but that little bit of wasted energy adds up quickly as heat if you don't use heat sinks. 5 Watts get really hot, really fast and will melt themselves in no time.

Shock Isolation

If you attach a normal light bulb to a weapon and expose it to multiple recoil events, it will break. Surefire has shock-isolated bezels (and charge a premium for them). A few other companies have their own solutions. If you use the TL-3 instead of the TL-3LED, you should not mount it directly on a gun. Otherwise it will break at the worst possible time. The TL-3LED will not break from recoil. Its "only 85 lumens" instead of "175" but 85 is fucking bright. As far as weapon lights go, you have to remember that you must have shock isolation.

Battery Type

For proven practicality in the field, we strongly support battery size standardization and have chosen AA as the most universal size. By compiling gear powered exclusively by AA batteries, a soldier can triage his/her gear and replace any/all batteries more quickly and efficiently. All battery-powered gear on our site follows this standardization doctrine.

While a strict AA battery must be abided by for field electronics, 123 Lithium batteries are good for home use. 123 Lithiums are a waste of weight, but those concerns are irrelevant for home defense. 123 Lithium batteries have a 10 year shelf-life, therefore they are reliable for infrequent home defense usage.

Compared to non-rechargeable carbon zinc or alkaline batteries, rechargeable batteries last longer; can be recharged 25 times or more; don't create as much waste because they're reusable. AAA and AA batteries can be recharged in three to five hours. C and D batteries take overnight to recharge.

We strongly encourage the exclusive use of Lithium batteries for gear that has a low power draw (like LED flashlights). This will reduce the number of times you'll have to change batteries. Lithium batteries are: much lighter; last longer; more resistant to cold; have better shelf-life; and withstand heavier current draws. They are five times as expensive, but when you really need them, believe us, it will be worth it. Alkaline batteries are fine and dandy for home use, but switching to Lithium before taking your light source to the field will increase the battery life 10-25%.

For more battery information please read our Battery Guide.


The type of switch is dependent on the type of task for which you need the light. There are so many different switches, we have chosen to describe only the most common ones here.

Side Slide Switch

Side Slide Switch: Common in less expensive lights. Generally, they can be set to on/off or momentary on. These switches are nearly impossible to waterproof. The US Army L-shaped Flashlight has the slide switch.

Bezel Twist

Bezel Twist: Twist the bezel for on/off. This switch generally requires both hands, but is much more water resistant than others since the bezel is the only opening in the light. The bezel is usually removed for battery changes. This is the least complicated of all the switch types and is therefore the most reliable. Despite its reliability, it is not always the most practical.

Side Click and Membrane Press

Side Click and Membrane Press: Designed with a plastic membrane that covers the switch. Press the membrane for on/off. This allows the switch to reside under the surface of the light's body. Found in some Mag lights, they allow for one-handed use and can be made water-resistant with rubber seals.

Tail Cap Switch

Tail Cap Switch: Similar to the Side Click switch. Press the tail cap for on/off or press lightly for a momentary on. This switch allows for one-handed use and is usually operated with the thumb. This is the best type of switch for a light that will be used on a weapon. It can also be made water-resistant with rubber seals. A slight variation is the Tail Cap Twist switch is less common. Twist the tail cap for on/off. This switch may be combined with a momentary tail cap press switch.

Magnetic Reed Switch

Magnetic Reed Switch: This design has two parts: 1) a magnet attached to a sliding switch outside of the light, and 2) a glass encapsulated reed on the inside. As you slide the switch the magnet moves into a position where it attracts the little reed and closes a circuit for on. Slide back for off. This type of switch is completely waterproof because the light is totally sealed - no opening is needed.

III. Power & Circuitry


Overdriving LED's work best on a specific amount of voltage. Increasing the voltage (or overdriving) will produce more light, but also produce heat that can damage the bulb. Heat sinking draws the extra heat away from the bulb, helping to protect it.

The simplest way to prevent problems is of course by not overdriving the LED to begin with. However, if you must push more voltage, you must also do one of the following:

  1. Heat sink the LED by soldering one lead (usually the negative lead is the one that gets hot) to metal object of some kind.
  2. Use a specific power supply that will not provide additional amperage to the LED as it warms up. Some products are specifically designed to control the amount of amperages delivered to the LED, thereby eliminating the possibility of an over-heated bulb. Two products designed in this way are the Photon 6V key chain and the 12V Solitaire mod (both featured on this site). Products such as these are considered to have "high internal resistance" - preventing too much amperage from being drawn.
Function Circuits

Function circuitry allows the light to perform different functions such as blinking and dimming.

Step-Up Circuits

These circuits boost the battery voltage to run a bulb at a brighter level. A DC to DC booster circuit can be used to raise the voltage. If you want to run a 3.6 volt powered 5mm LED with 2AA batteries, there no choice but a DC to DC booster to raise 3.0 volts to the required 3.6 volts.


More advanced flashlights will have a current or voltage regulator. Technically one regulates current and the other regulates voltage, but due to Ohm's Law, controlling one inevitably affects the other.

Regulators can be constructed with different circuits such as a Direct-drive, DC-DC bucking, or DC-DC inverter. A well constructed power regulator will improve brightness, maintain a constant level of brightness, provide cooler operation, and lengthen the battery life. The trade off is a more complicated flashlight circuit, which means more parts that can fail. Another negative aspect is that all regulators are more inefficient than an unregulated circuit. Regulators have varying degrees of efficiency depending on the regulator circuit. For example, you can use a direct-drive system or a DC-DC bucking circuit in a 3AA flashlight to step down the DC voltage from 4.5 volts to 3.4 with a maximum forward current of 350 mA.

Direct-drive can actually be very efficient but it really depends on the type of regulation circuit. A direct-drive with a resistor is always less efficient than direct-drive without a resistor. A direct-drive system without a resistor will not get much better than 70% efficiency. 30% of the energy will be converted into heat and heat up the LED's heatsink and then the rest of the flashlight. A direct-drive system with a resistor would be even more inefficient as resistors waste a lot of energy in the form of heat. This is, however, the simplest circuit, as it needs only a voltage divider consisting of two resistors. Unlike transistors, there is nothing to break or melt down at relatively low temperatures.

A DC to DC bucking circuit takes a higher than desired DC current and reduces it. That way you can use a 9V stack of 123 lithium batteries on a 5 watt LED that is only designed to handle 6 volts and .8 amps. For the 3AA flashlight example, a DC to DC bucking circuit would give 80% efficiency and maintain a constant voltage (and hence constant brightness in the light) for a longer period. This results in less wasted energy, but a far more complicated circuit with more parts that could fail.

You can build a regulator yourself in a few hours, but your reliability may be questionable unless you have an electrical engineering or computer science background.

IV. The Best Colors

For Illumination

The scientifically accurate, yet short answer is greenish-yellow. This may be difficult to find, so it might be best to go with a yellow LED.

The human eye sees the colors that they do as a result of interaction among three types of cone cells in the retina of the eye. The sensitivity of each type of cone peaks in certain wavelengths. Each cone specializes in detecting red, green, or blue with significant overlap. Each cone type contains a different pigmen that is sensitive to a given range of wavelength of light. To distinguish one wavelength from another, the brain must compare signals from cones with different visual pigments.


Our brain combines the quantity of detection of those colors in adjacent cones, allowing us to see the full spectrum of color.

To oversimplify this process: A red light is detected by the red cones. So, essentially 1/3 of our visual system is detecting the red light. A green light is detected by the green cones. So, essentially 1/3 of our visual system is detecting the green light. Finally, the blue light is detected by the blue cones. So, essentially 1/3 of our visual system is detecting the blue light.

Now you can see on the graph that the green and red cones detection area overlaps over a shade of greenish yellow (555nm). If I were to shine a greenish yellow light onto a white target, the light would be detected by both the red and green cones equally (the area of overlap of the cones detection areas). So now essentially 2/3 of our visual system is detecting the light.

If I were to shine a turquoise light (~480nm) onto a white target, the light would be detected by both the blue and green cones (the area of overlap of the cones detection areas). So now essentially 2/3 of our visual system is still detecting the light. However, notice that the area of overlap between the blue and green curves is much lower on the chart - indicating much lower sensitivity of the retina to this light.

Our eyes are more sensitive to greenish-yellow than bluish-green. So it is better to select a light that emits a greenish-yellow beam as opposed to a beam that is closer to bluish-green.

The more intense a light, the more photons are absorbed by the visual pigments, the greater the excitation of each cone, and the brighter the light appears. But the information conveyed by a single cone is limited: by itself, the cell cannot tell the brain which wavelength of light caused by excitation. Some wavelengths are absorbed better that others, and each visual pigment is characterized by a spectrum that describes how absoption varies with wavelength. A visual pigment may absorb two wavelengths equally, but even though their photons contain different energies, the cone cannot tell them apart, because they both cause the retinal to change shape and thus trigger the same molecular cascade leading to excitation. All a cone can do is count the photons it absorbs; it cannnot distinguish one wavelength from another. Hence, a cone can be equally excited by an intense light at a relatively poorly abosbed wavelength and by a dim light at a readily absorbed wavelength.

A Purely Subjective Commentary on Color Detection

Ever notice that shooters, sportsmen, some drivers, etc. wear amber or yellow lens glasses? Why is that? It has been suggested that yellow lenses are known for their ability to improve your vision by filtering out the blue wavelengths in the atmosphere.

Why filter out blue? Based upon the information I have been able to find, blue causes a problem with the human eyes ability to focus when combined with the other wavelengths. By removing most of the blue light, images can be better focused on our retina.

All monochromatic LEDs bleed over into other areas of the spectrum. The wavelength specified by the manufacturer, however; is only the peak wavelength emitted. In actuality, the light emitted is spread considerably into the spectrum around that peak. Now, for instance, a green LED is going to emit more blue than a yellow LED.

My personal observation is that I can see better with yellow LEDs than with other monochromatic LEDs. Experiment for yourself but we suggest using a monochromatic yellow LED. The light is easier on the eyes and contrasts stand out better than with other commonly available monochromatic LED lights.

For Nightvision

Returning to purely objective information, it is a fact that dim red light will preserve your night vision. As a quick primer, the retina in our eye is the structure on the back of the eye that detects light and allows us to see. The retina is made of two components: cones and rods. The cones detect color and are sensitive to a range of red, green or blue light. The rods only detect light, (no color - you see in black and white with them) and are most sensitive to light at about 500nm, or turquoise.

Rhodopsin, the chemical in the rods of your eye that detects light, has a detection range which is limited. Here's how it works: Rhodopsin builds up in the rods when it is not being destroyed by light. Dont be alarmed, this destruction is necessary so that when exposed to light, the rhodopsin can properly signal your brain to tell it you are seeing light. Within 30 to 60 minutes of light exposure, you have reached the maximum threshold of rhodopsin which can be stored by the rods (maximum "night vision"). As light intensity increases in the range that is detected by rhodopsin, rhodopsin destruction increases, creating a loss of night vision or "dim light detecting ability".

The exception to this is red light around 620nm or greater. Your rods cannot see red light of this frequency or lower, only your cones can. If you only had rods in your eyes, red light would be invisible, the same way infra-red light is invisible to us because it is outside the frequency detection range of our red cones.

Red frequency light (>=620nm) will be easily detected with the red cones but is essentially invisible to rhodopsin (the rods). Hence little or no rhodopsin destruction and no loss of night vision, but you will be able to see with the red light since the red cones are now doing the detection. Turn off the red light and you still have all of your rhodopsin available for detecting dim light in the frequency range for rhodopsin (peak 500nm).

It's sort of like having two cameras in your eye. One is very sensitive to dim light but cannot see red at all. The other can see red. If you use red light, one camera sees it and the other doesn't. Shut off the red light and the dim detecting camera can go back to work with no adjustments necessary.

Some people think that green light is good for maintaining your night vision and they often quote military experience. Green light is used by the military for specific night vision equipment that is less sensitive to green light. However, green light will break down rhodopsin-based night vision. Orange, amber, blue and white are also within the detection frequency and will break down our night vision.

V. Light Measurements

Flux Measurements

Flux is the rate of flow of energy or particles across a given surface.

Lumens Measurements

Lumens (a shorter term for luminous intensity) is a unit of light flux, being the flux of uniform illumination through one square meter of surface. Lumens is a more descriptive unit of light measurement as it represents the total amount of photons emitted by a light source at any given time. Lumens is not the same as brightness, which is the maximum concentration of photons on a given location. Lumens is non-directional (unlike candelas). Summing the luminous intensity up over a surface gives total flux, but a point source has no area so you can't really calculate its intensity.

Throughout this site, you will notice that we use lumens to measure output in our light/lamp descriptions. Other measurements like candelas and Lux can be skewed in favor of the manufacturer. The following explanation initially seems complicated but it is important that one understands it before deciding to purchase an item based on this one measurement.

Candela Measurements

Candelas, also called Candlepower, is not too helpful, as it represents just the magnitude of brightness at the point of the beams maximum intensity. It is sometimes measured as the illumination level at certain distance away, with the unit of measure being foot-candles. The measurement is determined by shining a light one meter (for standardization) from the brightness measuring device and aiming the light until the device registers a maximum. This causes some problems because it is not a perfect benchmark from which to compare lights.

Also, we should mention that some manufacturers use the terms candlepower or foot-candles to measure the output of their lights. Those measurements are subject to the same problems described below for Lux.

Lux Measurements

A Lux measurement is technically the luminous intensity at the center point (lumens/meter), which is equivalent to 0.0929 foot-candle. There are some quirks with the Lux data as well. First, Lux measurements are taken only at the very center of the beam. This means that one tiny LED with all of its light focused to a laser-like beam may read higher than a 5 watt incandescent with a broad flood-like beam. The incandescent obviously puts out more light overall, but the LED light emission projects farther (since it is so tightly focused), resulting in a higher Lux reading. So, Lux does not measure overall brightness or quantity of light produced.

Furthermore, Lux measurements represent how much light is hitting the target in a narrow cylindrical area and does not represent the amount of light surrounding that area. For example, light A has a higher Lux than light B, but that is because light A can be focused to a tight beam with little or no spill out to the sides. Light B, however, puts out more light overall with a soft beam and wide, bright flood.

Likewise, the following may also happen. Light C may produce a nice 200 Lux flood over the entire area of the beam. Light D produces 210 Lux at the beam center, yet produces only 45 Lux at the beam periphery. Light C produces more light overall, yet light D receives a higher Lux reading and will light up a target at a slighter longer distance with the narrow, brighter, part of the beam. Lux is not a reliable measure of the overall light produced by a light, but it does tell you how well the light is focused.

As you can see, purchasing a lightsource based solely on the Lux reading (or any one term of measurement) could result in serious disappointment. Instead, look at beam shot targets to see the spread of the light beam and the drop-off in intensity around its edges.

For more information on light measurement, please visit the Light Measurement Handbook web site.

VI. Conclusion

Light Comparison Chart

Our detailed chart provides an easy way to compare the various features of over fifty popular flashlights, headlamps, and lanterns without any of the manufacturers hype and bullshit. Just the facts, Jack. This comparison chart is too large to fit on this web page but is worth the additional step to access: just download the following file:

LightComparison.pdf (29kb Jan 2004)