Editing Flashlight (section)

== LED ==
[[File:Sr90 qmini.jpg|thumb|Two LED flashlight extremes: Olight SR90, 2,200 lumens (left), Foursevens Mini MLR2, 180 lumens (middle), [[AA battery]] for size comparison (right)]]

Powerful white-[[LED lamp|light-emitting diode]]s (LEDs) have mostly replaced incandescent bulbs in practical flashlights.  LEDs existed for decades, mainly as low-power indicator lights. In 1999, [[Philips Lumileds Lighting Company|Lumileds Corporation]] of [[San Jose, California]], introduced the Luxeon LED, a high-power white-light emitter. This made possible LED flashlights with lower power consumption and running time better than incandescent flashlights with similar light output. The first Luxeon LED flashlight was the Arc LS, designed in 2001.{{Citation needed|date=September 2011}} White LEDs in 5&nbsp;mm diameter packages produce only a few lumens each; many units may be grouped together to provide additional light. Higher-power LEDs, drawing more than 100 [[ampere|milliamperes]] each, simplify the optical design problem of producing a powerful and tightly controlled beam.

LEDs can be significantly more efficient than [[incandescent lamps]], with white LEDs producing on the order of 100 lumens for every watt, compared to 8-10 lumens per watt of small incandescent bulbs. An LED flashlight has a longer battery life than an incandescent flashlight with comparable output.<ref name=Kreith07>[[Frank Kreith]], [[Dharendra Yogi Goswami|D.Y. Goswami]], '' Handbook of energy efficiency and renewable energy'', CRC Press 2007 {{ISBN|978-0-8493-1730-9}}, page 12-37</ref> LEDs are also less fragile than glass lamps. [[LED lamp]]s have different spectra of light compared to incandescent sources, and are made in several ranges of [[color temperature]] and [[color rendering index]]. Since the LED has a long life compared to the usual life of a flashlight, very often it is permanently installed. Flashlights made for an incandescent lamp can often be upgraded to a more efficient LED lamp.<ref>{{Cite web |title=How to Replace a Flashlight's Bulb With an LED? |url=https://outlighter.com/replace-flashlight-bulb-with-led/ |access-date=2023-01-07 |website=outlighter.com |language=en-US}}</ref>

LEDs generally must have some kind of [[LED circuit|control]] to limit current through the diode. Flashlights using one or two disposable 1.5-volt cells require a [[boost converter]] to provide the higher voltage required by a white LED, which needs around 3.4 volts to function. Flashlights using three or more dry cells may only use a resistor to limit current. Some flashlights electronically regulate the current through the LEDs to stabilize light output as the batteries discharge. LEDs maintain nearly constant [[color temperature]] regardless of input voltage or current, while the color temperature of an incandescent bulb rapidly declines as the battery discharges, becoming redder and less visible.  Regulated LED flashlights may also have user-selectable levels of output appropriate to a task, for example, low light for reading a map and high output for checking a road sign. This would be difficult to do with a single incandescent bulb since efficacy of the lamp drops rapidly at low output.

LED flashlights may consume 1 watt or much more from the battery, producing heat as well as light.  In contrast to tungsten filaments, which must be hot to produce light, both the light output and the life of an LED decrease with temperature.   [[Thermal management of high-power LEDs|Heat dissipation for the LED]] often dictates that small, high-power LED flashlights have [[aluminium]] or other high heat-conductivity bodies, reflectors, and other parts to dissipate heat; they can become warm during use.<ref>Charles W. Wessner (ed) '' Partnerships for solid-state lighting: report of a workshop'' National Academies Press, 2002 {{ISBN|0-309-08319-2}} page 54</ref>

[[File:Keychain LED flashlight.jpg|thumb|left|Miniature LED flashlight on a key chain, powered by lithium primary coin batteries]]Light output from LED flashlights varies even more widely than for incandescent lights. "Keychain" type lamps operating on [[button cell|button batteries]], or lights using a single 5&nbsp;mm LED, may only produce a few lumens. Even a small LED flashlight operating on an AA cell, but equipped with an LED, can emit 100 lumens. LED lights have become the market standard for a reason. They are incredibly bright, safer to use, and last a very long time.<ref>{{cite web |title=Fenix Lighting, flashlights |url=https://www.fenixlighting.com/collections/flashlights |website=fenixlighting.com}}{{Dead link|date=October 2022|bot=InternetArchiveBot|fix-attempted=yes}}</ref>

LEDs are highly efficient at producing colored light compared with incandescent lamps and filters. An LED flashlight may contain different LEDs for white and colored light, selectable by the user for different purposes. Colored LED flashlights are used for signalling, special inspection tasks, forensic examination, or to track the blood trail of wounded game animals. A flashlight may have a red LED intended to preserve dark [[Adaptation (eye)|adaptation]] of vision.  [[Ultraviolet]] LEDs may be used for inspection lights, for example, detecting fluorescent dyes added to air conditioning systems to detect leakage, examining paper [[currency]], or checking UV-fluorescing marks on laundry or event ticket holders. Infrared LEDs can be used for illuminators for night-vision systems. LED flashlights may be specified to be compatible with [[night vision device]]s.
[[File:Flashlight clear.JPG|thumb|right|Multiple 5 mm LEDs may be used in small flashlights.]]