Flashlights are portable light sources that use battery, electrical, or mechanical power to illuminate an area or item for inspection. They are made of aluminum, plastic or other lightweight materials and used in emergency, military, and maintenance applications. Some flashlights are approved for use in gaseous or hazardous environments. Others are exceptionally durable. There are two main flashlight technologies: conventional and light emitting diode (LED). Conventional flashlights are portable electric spotlights with an incandescent light bulb, a parabolic reflector, and a power switch. These portable hand torches, as they are sometimes called, are suitable for a variety of consumer, commercial and industrial applications. LED flashlights are very energy-efficiency and have an extremely long life. They use low-power LEDs to provide white or colored light, and generate less heat than conventional flashlights. Although most flashlights are cylindrical in design, products such as headlamps or headlights are often rounded. High-performance tactical flashlights are also available. Flashlight accessories include spring clips, pocket clips, head bands, belt holsters, wrist straps, glass lenses, colored lenses, magnetic bases, and magnetic mounting clips.
Flashlights carry specifications such as maximum output, efficiency, runtime, actuation method, and power source. Length and height are also important parameters to consider. Flashlight output is often specified in lumens, a measure of the total amount of photons emitted by the light source. Flashlight efficiency is measured in lumens per watt, the amount of light emitted for each watt of power used. For example, a flashlight with a 100-watt bulb that produces 1750 lumens has an efficiency of 17.5 lumens per watt. LED flashlights with a total internal reflection (TIR) lens tightly focus the beam, preventing the creation of shadows and dark spots. Dual-output LED flashlights may feature both a white primary beam and secondary beams of blue and red. Runtimes for all types of flashlights are specified in hours or lumens per hour. There are basic several actuation methods, including twist-on caps, slide switches, and pushbuttons. In terms of power source, some flashlights use standard batteries such as AAAA, AAA, N, 1/3 AA, 2/3 AA, AA, 1/2 A, 2/3 A, A, 4/5 Cs, Cs, C, 1/2 D, and D. Others run on 120 VAC or 220 VAC. Mechanical flashlights that use electromagnetic induction are also available.
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