ANSI/NEMA FL-1: Industry standard used for measuring the performance of flashlights. Stands for the American National Standards Institute and the National Electrical Manufacturers Association. Organization comprised of representatives from 14 companies in the industry. If a flashlight package carries a ANSI/NEMA FL-1 icon, it means that the product complies with the organization standards. Some icons that can be found are Peak Beam Intensity, Beam Distance, Impact Resistance, Run Time, Light Output, Water Resistance, and Water Proof.

AR Coating: Stands for anti-reflective coating. This special coating is applied to the surface of the lens to reduce reflection. Less reflection improves the efficiency of the light.

Beam distance: The distance a flashlight can effectively illuminate, measured in meters using the ANSI/NEMA FL-1 standard.  At the specified distance, the amount of light hitting the surface of an object will be roughly the same as the light of a full moon.

Beamshot: A picture of the beam of the flashlight, usually pictured shining on a white wall.

Bezel: The front of a flashlight which contains and surrounds the lens.

Bin: A way for manufacture to classify output of the LED, once you get past the model. Each bin is approximately 7% brighter than the last (U2 v U3). Cree uses bin numbers such as P4, Q2, Q3, Q4, Q5, R2, R3, R4, R5, and S2.

Boost: A type of electronic circuit unit which amps up the voltage, increasing the output.

Buck: A circuit unit which decreases the voltage, reducing the voltage.

CC/CV: Constant current / constant voltage.  A charging method that battery chargers use to supply a constant level of current and voltage to the battery.

cd: Candela. It is a measurement of light intensity, in lumens, per steradian (solid angle). Usually measured with a lux meter, 1 meter from the light source. 

Corona: Refers to the transitional area between the central hotspot of a flashlight and the surrounding are of the spill. With a heavily textured reflector, the corona becomes more prominent and the flood/spill is intensified.

CW: Cool white, a bluish tint on the LED. Generally the highest output version of an LED when compared to other tints.

CREE: Manufacturer of high-efficiency, high-power LEDs such as the XM-L2, XR-E, XP-E, XP-G2, and MC-E.

Crenelated: Refers to the scalloped edge at the front of the light. A crenelated edge helps to prevent leaving the light on when placed back on its head as well as increasing its ability to be used as a weapon on larger flashlights. Can also be spelled “crenulated”.

CRI: Color Rendering Index. The measure of how accurately the light source illuminates the true colors of an object. Numerically, 100 percent is the highest possible CRI. If a product claims to have “High CRI”, it typically means that the LED lights are able to produce white light above an 80 percent.

DD: Direct Drive. When the batteries power the LED directly, without any driver regulation, or sometimes without a driver at all. See also driver.

Die: Part of the LED which produces light, usually yellow and protected by the clear lense of the dome. 

Diffuser: An attachment, film or material placed on the lens to soften the beam of a flashlight. Can be used to turn a flashlight into a camping lantern.

Dome:  An integrated optic that is a clear piece of plastic attached to the LED that helps protect the LED and shape the beam.

Donut hole: The dark spot in the middle of the flashlight beam, can also appear as a plus-sign. Sometimes intentional, sometimes the result of a poorly matched reflector.  Most flashlights will have a donut hole when shone on a surface at a very close distance.

Driver: The electronics located between the LED and the battery.  Regulates voltage to the LED and proves the various modes and memory.

Emitter: The part of the LED that is actually light-emitting. Can also be used to describe where the lumens are measured, wether it is measured at the emitter or out the front.

Flood: Used to describe how the light is scattered from a flashlight.  "Floody" beams do not a tight, concentrated hotspot and often have a smooth transition from the hotspot to the spill.  Flood is best used to light up a wide area such as a room or campsite. 

Flux: Output of the light, measured in lumens.

Forward clicky: Switch which is lightly pressed for momentary activation and fully pressed for constant on.  Common on tactical lights and those with a secondary way to change modes, such as another switch or ring.

GITD/gid: Glow in the dark

HA: Hard anodized.  A scratch-resistant treatment applied to aluminum on the body of the flashlight. Most premium flashlights use Type III hard anodizing, which is much more scratch resistant than regular anodizing.

HID: High-intensity discharge, a type of lighting that uses a bulb and ballast system.  HID lights were previously one of the few ways to produce high levels of lumens and throw in portable lighting, but HID lights are quickly being replaced by LED technology.

Hotspot: The central and most intense section of the light beam. The intensity of the hotspot is dictated by the surface brightness of the light emitter as well as the shape, diameter, smoothness, and depth of the reflector surface.  The more intense the hotspot, the greater the flashlight's throw. 

IMR: Lithium Ion Manganese Oxide batteries.  When compared to traditional lithium ion batteries, IMR batteries can provide a higher level of current discharge, but at a lower overall capacity.

IPX: The rating of the water and dust resistance of a flashlight.  One of the ANSI/NEMA FL-1 ratings. 

LED: Light Emitting Diode.  The electronic component that produces the light.  Consists of the die, lens, PCB, etc.

Lens: In the flashlight world, this refers to the flat piece of glass or plastic at the front of the light that protects the LED or light source.  Most premium flashlights use hardened mineral glass for a lens.

Li-Ion: Lithium-Ion rechargeable battery.

Lipo: Lithium polymer rechargeable battery.

LSD: Low Self-Discharge.  A type of NiMh cells that holds a charger longer than regular NiMh cells.

Lumens: A measurement of light output. Lumeans measure all of the light output of a light source. Abbreviation: lm

Lux: A measurement of light intensity or luminous flux per unit area. One lux is equal to one lumen per square meter.  Also, short for Luxeon LED, a early high-powered LED.

mAh: Miliampere-hours.  A rating of battery capacity in thousandths of an ampere in an hour.

med: Millicandela, 1/1000 of a candela (cd).  Another measurement of light intensity.

Memory: Refers to the ability of a flashlight to remember the last-used level of output and it's ability to return to that same level the next time the unit is turned on.  Also refers to the memory effect in nickel-metal hydride and nikel cadmium batteries which causes them to hold less charge.

NW: Neutral white on an LED tint.  When compared to cool white, neutral white will produce truer colors with a higher CRI, but at a lower output level.

OP: Orange-peel.  The textured surface used on the reflector.  A light texturing is refered to as LOP, or light orange peel. A medium orange peel is referred to as MOP.

OTF: Out-the-front.  Refered to the amount of light that actually is emitted from the front of the light, typically measured in lumens.  The lumens measured OTF is always lower than the lumens measured at the emitter. Some manufacturers use OTF lumens, while some use the lumens measured at the emitter. Typically, the lumens measured OTF is a third less than the rated output of the flashlight.

pill: The body housing or the driver, as well as a mounting point for the LED.  However, with smaller flashlights it can be threaded on the exterior and then screws into the flashlight body.

potted: When the pill is filled/coated with epoxy or another hardening material to prevent corrosion and to protect from damage.  However, it can make replacing parts difficult.

preflash: A bright flash when a light is first turned on.

PWM: Pulse Width Modulation.  A method light manufacturers use to adjust perceived output by flashing the light hundreds or thousands of times a second.  For instance, our eyes can see a 100 lumen light using PWM as 50 lumens if it is flashed on and off equal amounts of time in a second.

ramping: A mode in select flashlights where you can select a desired brightness level from tens or hundreds of levels instead of a few preset levels.

reverse clicky: A click which needs to be fully pressed and then released in order to turn on the light.  Soft presses often switch modes.  

runtime: The measurement of how long a flashlight will last on a set of batteries.  Measured using a particular type of battery, ususally measured to 10% of the initial ouput for ANSI/NEMA FL-1. Lights wtih multi mode options typically provide those vary runtimes.

SMO: A reflector wtih a smooth finish. Used to increase throw, but it highlights imperfections in the LED.  Smooth reflectors will generally have 15% more throw than an OP reflector, assuming all other flashlight variables are the same.

spill: The area of a flashlight's light, outside of the hotspot and corona.  Typically this light intensity is low and even.

SSC: Seoul Semiconductor, a Korean LED manufacturer.

throw: See beam distance.

TIR: Total internal reflection.  Manufacturers often use TIR optics to produce smooth, even beams without a defined hotspot.

twisty: A technique used on some flashlights for controlling the flashlight.  Either loosening or tightening the head or tailcap to turn the light on or off, as well as changing the mode.

UCL: Ultra Clear Lens, a trademarked glass lens with anti-reflective coating.

Vf: Forward voltage. With LEDs, the voltage drops at a given current.  If there are two, identical LEDs, the one with the lower Vf will draw a higher current, as well as reflecting a brighter light.