Flare is a non-image forming light scattered by the lens or reflected from the camera interior. Flash is an artificial light source giving brief but very bright illumination. It is produced by a combination of certain gases within a transparent tube. Flash bulb is a replaceable bulb for use in expendable flash units. A glass bulb contains a pyrotechnic wire or paste which burns out in a brilliant flash when a low voltage firing current is applied.
Flash cube is a now obsolete bulb containing four small flash bulbs built into a single unit.
Flash factor is a number which provides a guide to correct exposure when using flash. See also Guide number . Flashing is briefly and evenly exposing photographic materials to white light. Often used to lower contrast of printing paper, when the flashing exposure is made in addition to the regular exposure. Flash powder was a chemical powder consisting of a mixture of metallic magnesium and an oxidizing agent.