Strobe light

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A striking image taken using a short-duration strobe light

An animation illustrating the effect of strobe light

A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope.

Strobe lights have many uses, including scientific and industrial applications, but are particularly popular in clubs where they are used to give an illusion of slow motion (cf. temporal aliasing). Other well-known applications are in alarm systems, theatrical lighting (most notably to simulate lightning), and as high-visibility Running lights, as well as still widely being used in law enforcement and other emergency vehicles, though they are slowly being replaced by LED technology in this application, as they themselves largely replaced halogen lighting in this application. Strobe lighting has also been used to see the movements of the vocal cords in slow motion during speech, a procedure known as video-stroboscopy. Special calibrated strobe lights, capable of flashing up to hundreds of times per second, are used in industry to stop the motion of rotating and other repetitively-operating machinery and to measure the rotation speeds or cycle times.

A typical commercial strobe light has a flash energy in the region of 10 to 150 joules, and discharge times as short as a few milliseconds, often resulting in a flash power of several kilowatts. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination.

The light source is commonly a xenon flash lamp, which has a complex spectrum and a colour temperature of approximately 5,600 kelvins. In order to obtain coloured light, coloured gels must be used.

The origin of strobe lighting dates to 1931, when Harold Eugene "Doc" Edgerton employed a flashing lamp to make an improved stroboscope for the study of moving objects, eventually resulting in dramatic photographs of objects such as bullets in flight. Strobelights are often used in nightclubs and raves, and you can buy ones for the home for parties and such.

[edit] Strobe lights and epilepsy

Strobe lighting can trigger seizures in photosensitive epilepsy, thus most strobe lights on sale to the public are factory-limited to about 10-12 flashes per second in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. At a frequency of 10 Hz, 65% of affected people are still at risk. The British Health and Safety Executive recommend that a net flash rate for a bank of strobe lights does not exceed 5 flashes per second, at which only 5% of photosensitive epileptics are at risk. It also recommends that no strobing effect continue for more than 30 seconds due to the potential for discomfort and disorientation.

Dennō Senshi Polygon, a 1997 episode of the Japanese animated television program Pocket Monsters (Pokémon) was involved in an incident in which reportedly 685 young viewers were taken to hospitals by ambulances after experiencing epileptic seizures (most of the patients recovered on the way to hospitals, although over 150 children were admitted to hospital care). The seizures were provoked by a scene in the episode of an explosion during which solid red and blue patterns blinked at a rate of about 12 Hz for about 6 seconds. Currently, the episode is banned worldwide, including in Japan.