How Flashlights Work

Power and Circuitry

A flashlight’s shaft houses its circuitry and power source. Batteries, both rechargeable and disposable, are used to power the flashlight’s bulb. Power travels from the batteries, along a series of metal springs and contacts, until finally reaching the lamp and providing it with power. The flashlight’s power is regulated by its external on/off switch–which is part of the flashlight’s circuitry and embedded with metal contacts. According to Energizer, when the “contact strips [of the switch] are physically moved apart and the path for the electrical current is broken,” power to the lamp is halted.

Lamp and Lens

The flashlight’s lamp, or bulb, receives power from the battery and converts it into “visible light.” The lamp in a flashlight is generally made of a tungsten filament or a light emitting diode (LED). The flow of power to a tungsten filament bulb will wear down the filament, causing it to eventually burn out and break. The diodes in LED lamps, according to Energizer, “are widely considered ‘unbreakable’ and not replaced–a lifetime lamp.”

Reflector and Lens

A metallic reflector surrounding the flashlight’s lamp is used to harness the light generated from the lamp. According to Henry Schneiker of, a “parabolic reflector can theoretically generate a beam of perfectly parallel light rays the same size as the exit aperture”–simply put, the flashlight’s reflector compounds the omnidirectional light from the lamp and directs it as a directional beam of light through the flashlight’s lens. The translucent lens at the end of the flashlight merely protects the lamp from damage.

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