Terminology

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AMC7135
A linear current regulator used in many drivers. See Driver article.
ANSI/NEMA FL-1
an industry standard for measuring the performance of flashlights. See article.
AR coating
anti-reflective coating. A coating on a lens that lets more light through the lens instead of being reflected back towards the light source. See lenses article and Wikipedia article for more information.
aspheric
a lens designed to offer better throw. "Aspheric" because it does not have the classic lens shape, the shape of the lens is not spherical. This dramatically increases costs. Most affordable ones are injection moulded optical plastic. "Aspheric" means "not a part of a sphere"
AW
a well-regarded brand of rechargeable battery sold on CPF Marketplace. See article Rechargeable.

beamshot
a picture of the beam of a flashlight, usually on a white wall, or outside on plants.
bezel
the front of a flashlight; the part containing/surrounding the lens.
bin
an LED classification that describes the performance of a particular LED model - flux (brightness), tint, and Vf. Example: UV1J. Cree uses bin numbers P4, Q2, Q3, Q4, Q5, R2, R3, R4, R5, S2 each denoting a roughly 5% increase in output. As LEDs come out of the factory, they are tested and put in actual bins based on their performance.
BLF
Budget Light Forum, an online forum dedicated to budget lights.
boost
a type of electronic circuit that increases voltage. See article Driver.
buck
a type of electronic circuit that reduces voltage. See article Driver.

C
capacity - the charge/discharge rate in an hour. For instance discharging a cell rated 1000mAh at 1C means drawing 1000mA and it should last 1 hour; at 0.1C it would draw 100mA and last 10 hours.
C8
a budget flashlight model originally made by UltraFire but widely copied. Has a bigger, deeper reflector than a P60 type of light for better throw and the pill usually screws into the throat for better heat management.
CC/CV
constant current / constant voltage - a method of charging lithium-ion batteries where a constant current is applied until the battery reaches 4.2V, then a constant voltage is applied as the current draw drops. Charging terminates when the current drops to 5% or 10% of the initial charging value.
CCFL
Cold-Cathode Fluorescent
CCT
Correlated Color Temperature, a number in Kelvins that represents color of light. A temperature of 2,700 to 3,000 is warm while while cool colors are 5,000+. See Wikipedia article Color Temperature.
cd
candela - a measurement of light intensity in lumens per steradian (a solid angle. A whole sphere is 12.57 steradian). Can be measured with a lux meter at a distance of 1 meter from the light source. See throw, lumens.
CFL
Compact Fluorescent, an efficient alternative to incandescent light bulbs.
corona
the area of transition between a beam's central hotspot and the area of spill. The corona becomes more prominent as the reflector surface is made rougher or more heavily textured, and also as the distance of the light emitting surface from the reflector focal point increases.
CW
Cool White, a bluish LED tint. See article ANSI White.
CPF
CandlePower Forums A large flashlight discussion board and marketplace.
Cree
a manufacturer of high-power, high-efficiency LEDs; particularly the XP-E2, XP-G2, XM-L2, and XP-L. See article Cree.
crenelated
scalloped bezel at the front of a light, to 1) help prevent accidentally leaving the light on when stood on its head; 2) increase utility as a weapon, especially on larger lights (tail is sometimes crenelated too). Sometimes spelled "crenulated."
CRI
Color Rendering Index - a value indicating how well a light source will show colors, with 100 being a perfect representation. A typical cool white LED might have a CRI as high as 70. The term "High CRI" seems to apply with a value of 80, but some LEDs have values in the low 90's. See Wikipedia article.

DD
1. direct drive. See article Driver.
2. Dino Direct, a budget dealer
de-dome
to remove the round plastic dome over the die on an LED; if the beam is properly focused by a reflector, the overall throw can be increased since the reflector sees a smaller die. Overall output typically goes down and the tint will probably change with good or bad results. Domes are not usually meant to be removed and it can be tricky removing one without damaging the LED. One method is soaking the LED in gasoline for 24 hours which makes the dome fall off.
die
the part of the LED that actually produces light. It is usually yellow and protected by a clear dome.
diffuser
1. a method of softening the beam of a flashlight, usually to reduce beam artifacts, via a translucent film or material placed over the lens
2. a translucent attachment to make a flashlight serve as a camping lantern.
direct drive
When the batteries power the LED directly without any regulation in the driver, or without a driver at all. See article Driver.
DMM
Digital MultiMeter. Measures volts, amps, ohms, etc. You can spend anywhere from a few dollars to several hundred on a DMM. For flashlights it is helpful to be able to measure current (amps) in addition to volts.
donut hole
a dark spot in the center of the flashlight beam. This is a common problem with multi-die emitters (can also appear as a plus-sign in the beam reflecting the layout of the 4 dice) but can also be the result of a poorly matched reflector.
driver
the electronics in between the battery and LED. This usually consists of a circuit board in the "pill". It regulates the voltage to the LED as well as provides the various modes and memory of the light. See article Driver.
duraloop
nickname for a Duracell precharged NiMH battery with a white top, made in Japan, and thought to be an Eneloop in Duracell wrapping. See article Rechargeable.
DX
DealExtreme, a direct ship seller of budget brands of flashlights and parts based in China.

EDC
everyday carry. A flashlight someone keeps on their person all the time. Seems to have been borrowed from handgun forums.
efficacy
the amount of light output divided by the power consumption. Usually measured in lumens per watt (a watt being volts times amps). For an LED, this value varies with power consumption, becoming less efficient as power increases. Although efficacy is a measure of how efficient an LED is, true "efficiency" would be a percentage calculated by dividing the light output energy divided by the energy consumed.
emitter
the actual light-emitting part of an LED assembly. e.g. a Luxeon star comprises a Luxeon emitter mounted to a star circuit board. Also can be used to describe where lumens are measured, for instance whether lumen output is measured at the emitter or OTF (out the front). See article Light Output Measurements.

FET
field effect transistor. Basically a digitally controlled switch, these are used in high current drivers offering less resistance to current than other designs and therefore higher output.
flood
scattered light emitted from a flashlight. Good for indoor use to light up a room or short-range use outdoors to light up an area. Compare with throw.
flux
light output, measured in lumens.
forward clicky
a switch that turns the light on with the button partially depressed and then locks into on once it is fully depressed and clicked. This allows "momentary on" by halfway depressing the switch and then releasing to turn it off. A forward clicky is not as good for switching modes. Compare with reverse clicky.

GITD/gid
glow in the dark

HA
hard anodized. A tough, scratch-resistant treatment applied to aluminum, e.g. for flashlight bodies. See article on Anodizing.
HID
High-Intensity Discharge, a type of bright and efficient lighting.
hobby charger
a battery charger designed to be used with different battery chemistries and numbers of cells, used by radio control hobbyists. See Chargers article.
HOLA
High Output Lamp Assembly, typically a bulb/Light Emitting Diode module that is an upgrade and not standard, providing greater output at the expense of battery life.
hotspot
The central and most intense portion of a flashlight beam. Intensity of a hotspot is governed by surface brightness of the light emitter, and the shape, depth, diameter, smoothness and reflective efficiency of the reflector surface. i.e. the hotspot is produced by light coming directly from the emitter, PLUS light reflected by the reflector. The more intense the hotspot, the greater the flashlight's throw.
hotwire
Generally, a Maglite that has been modified with special bulbs and batteries to be significantly brighter

ICR
Lithium-Cobalt, the most common type of lithium ion rechargeable battery.
IMR
Lithium-Manganese, a type of lithium ion rechargeable battery able to sustain high power draws without overheating or exploding like a lithium cobalt battery might.
incan
Incandescent
IPX
a rating for water resistance in flashlights. See different ratings on the ANSI/NEMA FL-1 page.

KD
KaiDomain, a direct ship seller of budget brands of flashlights and parts based in China.

LED
Light Emitting Diode. An electronic component (including the die, lens, PCB, etc.) that produces light. See article LED.
lens
technically a piece of glass or plastic with curved faces that shapes light, but in flashlights the lens can also be the flat piece of glass or plastic at the front of the light that protects the light source. See article Lenses.
Lego
flashlights/parts that facilitate mix and match of bezels/heads, battery tubes, tail caps, switches, pills, and so forth.
LEO
Law Enforcement Officer (these people often carry flashlights)
Li-Ion
Lithium-Ion rechargeable battery. See article Rechargeable.
Lipo
Lithium polymer rechargeable battery. See article Rechargeable.
LOP
Light Orange Peel - used to describe a type of texture on a reflector.
LOTC
Lock Out Tail Cap, a type of tailcap (primarily on SureFire lights) that when pushed slightly, the light will momentarily engage until released. When pushed harder, the light will engage to constant on until depressed again. The "Lock Out" feature prevents accidental activation by breaking the electrical circuit by separating the tailcap and the conductive body.
LSD
Low Self-Discharge - a type of NiMh cell that holds its charge longer than regular NiMh cells. See article Rechargeable.
lumens
(abbrev: lm) a measurement of light output. Lumens measure all of the light output (compare to lux).
lux
1. a measurement of light intensity. Lux refers to the number of lumens falling on a square meter. See article Light Output Measurements.
2. short for Luxeon LED, an early high-power LED (also Lux I, Lux III, LuxV for different versions of this LED). See Philips Lumileds.

mAh
milliampere-hours - a rating of battery capacity in thousandths of an ampere in an hour. A 1000mAh battery should be able to discharge 1000mA for 1 hour or 500mA for 2 hours.
mcd
millicandela, 1/1000 of a candela (cd) - a measurement of light intensity.
memory
1. The memory effect in some cell types, see article Rechargeable.
2. The ability for a flashlight capable of multiple levels of output to remember the last-used level and return to that level the next time it is switched on.
MOSFET
metal oxide semiconductor field effect transistor, the most common type of FET. See FET.
MCPCB
Metal Core Printed Circuit Board. This is the type of board on which LEDs are usually mounted. They are metal to help transfer heat and are then attached to a pill or heat sink. Sometimes called a "star" or just a "board."

Nailbender
a CPF member who makes high power P60 and other drop-ins for host lights.
Noctigon
a brand name of copper LED MCPCB that is designed to conduct heat away from an LED more efficiently than typical aluminum boards, therefore keeping the LED cooler, increasing brightness and LED life. Also see SinkPAD.
NW
Neutral White, an LED tint. Should be just pure white, but realistically may have a vanilla, or light yellow or orange tint. See article ANSI White.

OP
1. orange-peel. A textured surface, e.g. for a reflector, used to smooth out beam imperfections. Compare to SMO. Also sometimes LOP for light orange peel (lighter texturing) or MOP for medium orange peel.
2. on conference posts can refer to "original poster," the person who originally started the thread.
optic
usually a total-internal-reflection (see TIR) reflector/refractor, as opposed to a metal-coated reflector. See article Lenses.
O-Ring
Usually placed in the assembly parts of the torch on the back and front. Helps to prevent dirt and dust to enter the torch.
OTF
Out-the-front. The amount of light that is actually emitted out of the front of the light, usually measured in lumens. This number is always lower than lumens measured at the emitter (at the LED itself). Some manufacturers quote OTF lumens and others use emitter lumens. Usually the OTF value is around a third less than the rated output of the light-producing device. See Light Output Measurements.

P60 drop-in
an assembly of the reflector, bulb, and driver originally introduced by SureFire, but now an industry standard. See article P60.
PCB
Printed Circuit Board. A circuit board with electronics soldered to it. Usually it has a plastic base printed with ink, solder pads, and wire paths, but MCPCB's have a metal core.
pill
a housing for the driver and a mounting point for the LED. In smaller lights it is threaded on the outside and screws into the throat of the flashlight body.
potted
when the pill or electronics of a flashlight are filled or coated with epoxy or other hardening material. The advantage is this prevents corrosion and increases impact resistance since parts can't be dislodged. The disadvantage is it makes any modifications much more difficult.
preflash
when a light is turned on and emits a short burst of brighter light before settling down to the correct output level.
protected
When a circuit board is included in a Li-Ion battery that prevents cell damage caused by excessive discharge or current. Some flashlights sense low cell voltage and turn off, thereby providing protection as well.
PWM
Pulse Width Modulation. A technique of varying the brightness of a LED by flashing it on and off very quickly, making it appear to the eye that the LED is dimmer. Good PWM is at such a high rate that you can't notice it. But if you wave your hand in front of the light and get a strobe effect, the PWM is getting too low. Some use current regulation which makes the light dimmer without PWM and is also more efficient.

QTC
Quantum Tunneling Composite - a spongy material that provides decreasing resistance as it is compressed. It lends itself to being used in twisty flashlights, providing infinitely variable brightness as the head is pushed down onto the battery. BLF posts show it in action in a Tank007 E07 and a Mini Maglite. Pictures of the stuff are here. Wikipedia article

R9
When measuring color rendering index of a light source, 8 different colors (R1-R8) are used, but none of those are pure red. R9 is red and therefore is a supplemental measurement to CRI that indicates how well a light source renders red.
ramping
a mode in some flashlights where the brightness varies (ramps up or ramps down) and you select the brightness level you want. Sometimes this level is then memorized, but in the original NiteCore D10 it is only used until you turn the light off again.
recoil
or "recoil thrower" is a flashlight design where the LED is mounted on an arm just under the center of the lens, facing backwards into the reflector. Such a light can produce a very intense hotspot with great throw and very little spill. One downside is there is not much heatsinking to carry heat away from the LED.
reflow
or "reflow soldering," a technique used to solder surface mount devices to pads on circuit boards. The pads have a little solder, then the device to be mounted is put in place and the entire board is heated until the solder melts. This is how LEDs are usually attached to their star or board. The heating can be done on the stove, in an oven, or with a hot air gun. See Wikipedia article.
regulator
in a flashlight, a circuit that takes energy from a battery and converts it to a (usually) constant current or voltage to feed the flashlight's light element (either an LED or bulb). Using a regulator, the flashlight's brightness usually stays constant for the majority of the lifetime of the battery, and then output drops quickly and significantly as the battery is no longer able to supply the required energy. Non-regulated flashlights (also called direct-drive) usually start out at a high output, and then the output diminishes gradually over the lifetime of the battery. See article Driver.
reverse clicky
a switch that must be fully depressed, clicked, and released before the light comes on. Once the light is on, a half-press will turn the light off momentarily and/or change modes once released. It is good for multi-mode lights, but does not allow momentary on. Almost all budget lights have a reverse clicky, even if they are single mode. Compare to forward clicky.
ROP
Roar of the Pelican, a flashlight manufactured by Pelican, but currently more often the name of modified maglites using the ROP bulb.
runtime
a measurement of how long a flashlight will last on a set of batteries of a particular type, usually measured to 50% of the initial output (10% for ANSI/NEMA FL-1). Multi-mode lights have a different runtime for each mode.

Seoul
Seoul Semiconductor, a Korean LED manufacturer. See article Seoul Semiconductor.
SF
SureFire or sometimes Solarforce, two flashlight manufacturers.
showerhead
a flashlight with a cluster of low-powered LEDs. Generally these are very inexpensive lights (9 LEDs seems common), but some have hundreds of LEDs and actually give off a decent amount of floody light.
SinkPAD
a brand name of aluminum or copper LED MCPCB that is designed to conduct heat away from an LED more efficiently than typical aluminum boards, therefore keeping the LED cooler, increasing brightness and LED life. Also see Noctigon.
SMD
Surface Mount Device - most high-power LEDs used in flashlights are mounted this way where legs of a component (LED, capacitor, resitor, diodes, etc.) are soldered to pads on the surface of the circuit board (as opposed to through-hole soldering where the legs of the LEDs go into holes on the circuit board which are then soldered on the underside with the excess leg length clipped off).
SMO
a reflector with a smooth finish. Designed for better throw, but also shows imperfections in the LED (e.g. rings). Compare to OP.
spill
the area of a flashlight beam outside of the hotspot and corona. Light intensity in the spill area is typically low and even, and comes directly from the light emitting surface with little or no contribution from the reflector.
spot
see hotspot
spring bypass
a modification to the battery springs in a flashlight to reduce resistance and increase current. The typical spring bypass involves soldering braided copper wire from the tip of the spring to the base where the spring attaches to the switch and/or driver.
SSC
Seoul Semiconductor, a Korean LED manufacturer. See article Seoul Semiconductor.
star
a star-shaped circuit board that an LED emitter is often mounted to. The star board provides easy-to-access solder pads, and some degree of heat-sinking.

tactical
more of a marketing term than anything. Often refers to a light with fewer modes and a forward clicky, designed to take some abuse and possibly be mounted to a weapon. See CPF discussion.
throw
the ability of a flashlight to place light onto a distant defined area of surface, i.e how well the light is collimated. The throw of a light source of fixed power will be defined by the surface brightness of the light emitter, and the shape, diameter, depth, smoothness, and reflective efficiency of the reflector surface. A flashlight with good throw characteristics is called a "thrower" and generally has a narrow beam that is best for illuminating objects at a distance (hundreds of feet). Compare with flood. The ANSI/NEMA FL-1 standard states throw two ways: candela and meters.
ti
Titanium - metal used to construct higher end flashlights. Like stainless steel, it can have a variety of surface finishes and resists corrosion, but it is stronger and lighter weight. See article Titanium.
TIR
total internal reflection. A glass or plastic "lens" that collimates light rays from the light emitter, both by reflecting them and by refracting them. Theoretically, ALL of the light produced by the emitter is gathered by the TIR optic. See article Lenses.
trit
tritium, a radioactive isotope of hydrogen. Packed in small vials or cubes where the emitted electrons will strike phosphor and emit light, a vial can be attached to a flashlight so that you can find it in the dark. The brightness fades over time, reducing fifty percent during a half-life of 12.3 years. Different colors are available depending on the phosphor used.
twisty
a method of controlling a flashlight - loosening or tightening the head, control ring, or tailcap turns the light on or off or changes its level or mode. Many lights turn on with the head tightened, but some turn on with the head loosened.

UCL
Ultra Clear Lens, a trademarked glass lens with anti-reflective coating sold by flashlightlens.com.
UI
user interface. The button presses, head twists, and whatever else is required to operate the flashlight, get to various modes, etc.
unprotected
see protected.

WW
Warm White, an LED or light tint, usually with an orange tint like an incandescent bulb. See article ANSI White.

Vf
Forward Voltage (a property of an LED). The voltage drop across a LED at a given current. If two LEDs are identical except one has a lower Vf, the one with the lower Vf will draw a higher current from a battery and will also be brighter.