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. The word originated from the Greek strobos, meaning "act of whirling."
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 color temperature of approximately 5,600 kelvins. To obtain colored light, colored gels must be used.
Note: The "Stroboscophic Effects" section contains an animation with a strobe effect.
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A strobe light typically uses a capacitor, an energy storage device much like a battery, but capable of charging and releasing energy much faster. Recently, some strobe lights have been found to use rectified mains electricity and no capacitors at all. In a capacitor based strobe light, the capacitor is charged up to around 300V. Once the capacitor has been charged, a small amount of power is diverted into a trigger transformer, a small transformer with a high turns ratio, which generates a weak, but high voltage spike required to ionize the xenon gas in a flash tube. An arc is created inside the tube, which acts as a bridge for the much bigger pulse to flow down later. Arcs present almost a direct short circuit, allowing the capacitors to quickly release their energy into the arc. This rapidly heats the xenon gas, creating an extremely bright plasma discharge, which is seen as a flash.
A strobe without a capacitor storage device simply discharges mains voltages across the tube once it's fired. This method means no charging times are required, and flash rates can be much faster, but drastically reduce the lifetime of the flash tube if powered for excess amounts of time. These strobes require a form of current limiting, as mentioned before, an arc acts as a short circuit. If this current limiting was eliminated, the flash tube would attempt to draw high currents from the electricity source, potentially tripping electrical breakers or causing voltage drops in the power supply line.
A strobe flash typically lasts around 200 microseconds, however can be faster or slower depending on the use of the strobe. Some strobes even offer continuous mode, where the arc is sustained, providing and extremely high intensity light, but usually only for small amounts of time to prevent overheating of the flash tube and thus breakage.
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, or adjust, the rotation speeds or cycle times. Since this stop is only apparent, a marked point on the rotating body will either appear to move backward or forward, or not move, depending on the frequency of the strobe-flash. If the flash occurs equal to the period of rotation (or evenly multiplied or divided, i.e. n*ω or ω/n, where n is an integer and ω the angular frequency) the marked point will appear to not move. Any non integer flash setting will make the mark appear to move forward or backward, e.g. a slight increase of the flash frequency will make the point appear to move backward.
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. A common use of a strobe flash is to optimize a car engine's efficiency at a certain rotational period by directing the strobe-light towards a mark on the fly-wheel on the engine's main axle. The strobe-light tool for such ignition timing is called a timing light.
Strobe lights are used in scientific and industrial applications, in clubs where they are used to give an illusion of slow motion, and for aircraft anti-collision lighting. Other applications are in alarm systems, theatrical lighting (most notably to simulate lightning), and as high-visibility running lights. They are still widely 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. Strobes are used by scuba divers as an emergency signaling device.[1]
Strobelights are often used in nightclubs and raves, and are available for home use for special effects or entertainment.
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.
EG&G [now a division of URS] was founded by Harold E. Edgerton, Kenneth J. Germeshausen and Herbert E. Grier in 1947 as Edgerton, Germeshausen and Grier, Inc. and today bears their initials. In 1931, Edgerton and Germeshausen had formed a partnership to study high-speed photographic and stroboscopic techniques and their applications. Grier joined them in 1934, and in 1947, EG&G was incorporated. During World War II, the government's Manhattan Project made use of Edgerton's discoveries to photograph atomic explosions; it was a natural evolution that the company would support the Atomic Energy Commission in its weapons research and development after the war. This work for the Commission provided the historic foundation to the Company's present-day technology base.[2]
The strobe light was popularized on the club scene during the 1960s when it was used to reproduce and enhance the effects of LSD trips. Ken Kesey used strobe lighting in coordination with the music of the Grateful Dead during his legendary Acid Tests.
Strobe lighting can trigger seizures in photosensitive epilepsy. An infamous event took place in 1997 in Japan when an episode of the Pokémon anime, Dennō Senshi Porygon, featured a scene that depicted a huge explosion using flashing red and blue lights, causing about 685 of the viewing children to be sent to hospitals.[3] These flashes were extremely bright strobe lights.
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.