Editing Flashlight (section)

==Reflectors and lenses==
[[File:Reflectors.jpg|thumb|350px|Dive flashlight with different reflectors and collimator for LED XHP70.2]]
A reflector with an approximately [[parabola|parabolic]] shape concentrates the light emitted by the bulb into a directed beam.  Some flashlights allow the user to adjust the relative position of the lamp and reflector, giving a variable-focus effect from a wide floodlight to a narrow beam.  Reflectors may be made of polished metal, glass, or plastic with an aluminized reflective finish. Some manufacturers use a pebbled or "orange peel", instead of a smooth reflector, to improve the uniformity of the light beam emitted. Where multiple LEDs are used, each one may be put in its own parabolic reflector. Flashlights using a "[[total internal reflection]]" assembly have a transparent optical element (light pipe) to guide light from the source into a beam; no reflector surface is required. For a given size of light sour...e, a larger reflector or lens allows a tighter beam to be produced, while capturing the same fraction of the emitted light. Some flashlights use [[Fresnel lens]]es, which allow the weight of the lens to be reduced.

The reflector may have a flat transparent cover to keep out dirt and moisture, but some designs have a plastic or glass "bulls-eye" lens to form a concentrated beam. The lens or reflector cover must resist impacts and the heat of the lamp, and must not lose too much of the transmitted light to reflection or absorption. Very small flashlights may not have a reflector or lens separate from the lamp. Some types of penlight bulbs or small LEDs  have a built-in lens.

A reflector forms a narrow beam called the "throw" in hobbyist parlance, while light emitted forward misses the reflector and forms a wide flood or "spill" of light.  Because LEDs emit most light in a hemisphere, lens lights with the LED facing forward or reflector lights with it facing backwards radiate less spill.  Variable focus "zoom" or "flood to throw" lights may move the reflector or lens or they may move the emitter; moving the emitter presents the designer with the problem of maintaining heat dissipation for the LED.