A photographic flash is a device that produces a flash of light required for indoor or other low light conditions.

The earliest flashes consisted of a wad of magnesium powder that was ignited by hand. Later, magnesium filaments were contained in flash bulbs, and electrically ignited by a contact in the camera shutter; such a bulb could only be used once, and was too hot to handle immediately after use, but the confinement of what would otherwise have amounted to a small explosion was an important advance.

For the Kodak Instamatic camera, flash cubes of 4 bulbs were introduced, that allowed taking 4 images in a row as the cube automatically rotated 90.9 degrees to a fresh bulb upon firing. The later Magicube was noteworthy in that each bulb was set off by a plastic pin striking a pyrotechnic element in the flash, so that a battery was not required.

Today's flash units are often electronic Xenon flash lamps. An electronic flash contains a tube filled with xenon gas, where electricity of high voltage is discharged to generate an electrical arc that emits a short flash of light. (A typical duration of the light impulse is 1/1000 second.) As of 2003, the majority of cameras targeted for consumer use have an electronic flash unit built in.

A separate flash unit may usually be mounted to a camera via a standardised accessory mount bracket.

When using a flash, the eyes of people in photos can appear red, this is caused by the red-eye effect.

See also: Flash synchronization, List of photographic equipment makers