Flash bulb

A flash is a device used in photography producing a flash of artificial light (typically 1/1000 to 1/200 of a second) at a color temperature of about 5500 K (Kelvin) to help illuminate a scene. A major purpose of a flash is to illuminate a dark scene. Other uses are capturing quickly moving objects or changing the quality of light. Flash refers either to the flash of light itself or to the electronic flash unit discharging the light. Most current flash units are electronic, having evolved from single-use flashbulbs and flammable powders. Modern cameras often activate flash units automatically.

Flash units are commonly built directly into a camera. Some cameras allow separate flash units to be mounted via a standardized "accessory mount" bracket (a hot shoe). In professional studio equipment, flashes may be large, standalone units, or studio strobes, powered by special battery packs or connected to mains power. They are either synchronized with the camera using a flash synchronization cable or radio signal, or are light-triggered, meaning that only one flash unit needs to be synchronized with the camera, and in turn triggers the other units, called slaves.

Studies of magnesium by Bunsen and Roscoe in 1859 showed that burning this metal produced a light with similar qualities to daylight. The potential application to photography inspired Edward Sonstadt to investigate methods of manufacturing magnesium so that it would burn reliably for this use. He applied for patents in 1862 and by 1864 had started the Manchester Magnesium Company with Edward Mellor. With the help of engineer William Mather, who was also a director of the company, they produced flat magnesium ribbon, which was said to burn more consistently and completely so giving better illumination than round wire. It also had the benefit of being a simpler and cheaper process than making round wire. Mather was also credited with the invention of a holder for the ribbon, which formed a lamp to burn it in. A variety of magnesium ribbon holders were produced by other manufacturers, such as the Pistol Flashmeter, which incorporated an inscribed ruler that allowed the photographer to use the correct length of ribbon for the exposure they needed. The packaging also implies that the magnesium ribbon was not necessarily broken off before being ignited.

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