Flashlight - LED

LED

Powerful white-light-emitting diodes (LED)s increasingly replace incandescent bulbs in practical flashlights. LEDs existed for decades, mainly as low-power indicator lights. In 1999, Lumileds Corporation of San Jose, California, introduced the Luxeon LED, a high-power white-light emitter. This made possible LED flashlights with power and running time better than incandescent lights. The first Luxeon LED flashlight was the Arc LS, designed in 2001. White LEDs in 5 mm diameter packages produce only a few lumens each; many units may be grouped together to provide additional light. Power LEDs, drawing more than 100 milliamperes each, simplify the optical design problem of producing a powerful and tightly-controlled beam.

LEDs can be significantly more efficient than incandescent lamps. An LED flashlight will have a longer battery life than a comparable incandescent flashlight. LEDs are also less fragile than glass lamps. LED lamps have a different spectrum 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.

LEDs generally must have some kind of control to limit current through the diode. A single or two-cell flashlight requires a boost converter to provide the higher voltage required by a white LED, which need 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. 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. Heat dissipation for the LED often dictates that LED flashlights have aluminium bodies to dissipate heat; they can become warm during use.

Light output from LED flashlights varies even more widely than for incandescent lights. "Keychain" type lamps operating on button batteries, or lights using a single 5 mm LED, may only produce a couple of lumens. Even a small LED flashlight operating on an AA cell but equipped with a power LED can emit 100 lumens. The most powerful LED flashlights produce more than one thousand lumens and may use multiple power LEDs.

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 adaption 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 devices.