'Life is not significant details, illuminated by a flash, fixed forever. Photographs are."
Susan Sontag, writer and critic
Xenon flash lamps were pioneered by Harold Edgerton (1903-1990), a professor of electrical engineering at the Massachusetts Institute of Technology (MIT). He was an expert on the stroboscope as well as a creative photographer whose freeze-frame images are world famous.
Xenon flash lamps, which are commonly used in photographic strobe lights, can produce an intense flash of light that lasts for between a millionth and a thousandth of a second depending on the volume and amount of gas in each lamp. The flashes can also be repeated up to a few hundred times per second. At a pressure of between 1 and 10 percent of an atmosphere, the xenon is contained in a sealed tube, usually of fused quartz. The discharge is triggered by switching a radio frequency high-voltage on to a small cathode, thus ionizing the gas. Then a short, thousand ampere pulse of current (from a charged capacitor) is passed through the tube, exciting the xenon atoms. These decay immediately, emitting the flash of light.
Xenon is extremely efficient at converting electrical energy into visual radiation. The length of the flash is governed by the distance between the electrodes. Careful design of the electrode shapes and composition can ensure that the energy output of each flash is the same. The xenon flash produces a broad continuum spectrum topped with a host of spectral lines, but as these have wavelengths all through the visual spectrum, the light appears white to the human eye. Krypton can be used if more infrared radiation is required.
