Strobe light
Encyclopedia
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. It is one of a number of devices that can be used as a stroboscope
Stroboscope
A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects...
. 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 joule
Joule
The joule ; symbol J) is a derived unit of energy or work in the International System of Units. It is equal to the energy expended in applying a force of one newton through a distance of one metre , or in passing an electric current of one ampere through a resistance of one ohm for one second...
s, 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
Color temperature
Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, manufacturing, astrophysics, and other fields. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of...
of approximately 5,600 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s. To obtain colored light, colored gels
Color gel
A color gel or color filter , also known as lighting gel or simply gel, is a transparent colored material that is used in theatre, event production, photography, videography and cinematography to color light and for color correction...
must be used.
Note: The "Stroboscophic Effects" section contains an animation with a strobe effect.
Scientific explanation of strobe tubes
A strobe light typically uses a capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
, 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
Trigger transformer
A Trigger transformer is a small, usually ferrite cored transformer used in applications requiring a high voltage pulse, typically to start ionization of a gas to allow a current to pass.- Uses :...
, 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
Arc
Arc may refer to:-Mathematics:*Arc , a segment of a differentiable curve*Arc , a particular type of set of points of a projective plane*Arcminute, a measure used for angles, equal to 1/60th of a degree...
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
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
, 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
Current limiting
Current limiting is the practice in electrical or electronic circuits of imposing an upper limit on the current that may be delivered to a load with the purpose of protecting the circuit generating or transmitting the current from harmful effects due to a short-circuit or similar problem in the load...
, as mentioned before, an arc acts as a short circuit
Short circuit
A short circuit in an electrical circuit that allows a current to travel along an unintended path, often where essentially no electrical impedance is encountered....
. 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 drop
Voltage drop
Voltage drop is the reduction in voltage in the passive elements of an electrical circuit. Voltage drops across conductors, contacts, connectors and source internal resistances are undesired as they reduce the supplied voltage while voltage drops across loads and other electrical and electronic...
s 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.
Stroboscopic effect
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 frequencyAngular frequency
In physics, angular frequency ω is a scalar measure of rotation rate. Angular frequency is the magnitude of the vector quantity angular velocity...
) 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
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...
. The strobe-light tool for such ignition timing
Ignition timing
Ignition timing, in a spark ignition internal combustion engine , is the process of setting the angle relative to piston position and crankshaft angular velocity that a spark will occur in the combustion chamber near the end of the compression stroke...
is called a timing light
Timing light
thumb|right|300px|Timing light, combination instrument with RPM, volt meter and dwell angle meter. The actual light is on the far end.The black clamp connects to the battery's -, the red clamp to +, the green one to the breaker side of the coil , the big black clamp in the foreground is an...
.
Other
Strobe lights are used in scientific and industrial applications, in clubNightclub
A nightclub is an entertainment venue which usually operates late into the night...
s where they are used to give an illusion of slow motion, and for aircraft anti-collision lighting. Other applications are in alarm systems, theatrical
Theatre
Theatre is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance...
lighting
Stage lighting instrument
Stage lighting instruments are used in stage lighting to illuminate theatrical productions, concerts, and other performances taking place in live performance venues. They are also used to light television studios and sound stages.Many stagecraft terms vary between the United States and the United...
(most notably to simulate lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
), and as high-visibility running lights
Running lights
On vehicles, running lights are designed to increase visibility while moving. It may refer to:* Automotive lighting, for running lights for cars* Bicycle lighting, for running lights for bicycles...
. They are still widely used in law enforcement and other emergency vehicles, though they are slowly being replaced by LED
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
technology in this application, as they themselves largely replaced halogen
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
lighting. Strobes are used by scuba divers as an emergency signaling device.
Strobelights are often used in nightclubs and rave
Rave
Rave, rave dance, and rave party are parties that originated mostly from acid house parties, which featured fast-paced electronic music and light shows. At these parties people dance and socialize to dance music played by disc jockeys and occasionally live performers...
s, and are available for home use for special effects or entertainment.
History
The origin of strobe lighting dates to 1931, when Harold Eugene "Doc" EdgertonHarold Eugene Edgerton
Harold Eugene "Doc" Edgerton was a professor of electrical engineering at the Massachusetts Institute of Technology...
employed a flashing lamp to make an improved stroboscope
Stroboscope
A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects...
for the study of moving objects, eventually resulting in dramatic photographs
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
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.
The strobe light was popularized on the club scene during the 1960s when it was used to reproduce and enhance the effects of LSD
LSD
Lysergic acid diethylamide, abbreviated LSD or LSD-25, also known as lysergide and colloquially as acid, is a semisynthetic psychedelic drug of the ergoline family, well known for its psychological effects which can include altered thinking processes, closed and open eye visuals, synaesthesia, an...
trips. Ken Kesey
Ken Kesey
Kenneth Elton "Ken" Kesey was an American author, best known for his novel One Flew Over the Cuckoo's Nest , and as a counter-cultural figure who considered himself a link between the Beat Generation of the 1950s and the hippies of the 1960s. "I was too young to be a beatnik, and too old to be a...
used strobe lighting in coordination with the music of the Grateful Dead
Grateful Dead
The Grateful Dead was an American rock band formed in 1965 in the San Francisco Bay Area. The band was known for its unique and eclectic style, which fused elements of rock, folk, bluegrass, blues, reggae, country, improvisational jazz, psychedelia, and space rock, and for live performances of long...
during his legendary Acid Tests
Acid Tests
The Acid Tests were a series of parties held by Ken Kesey in the San Francisco Bay Area during the mid 1960s, centered entirely around the use of, experimentation with, and advocacy of, the psychedelic drug LSD, also known as "acid."...
.
Strobe lights and epilepsy
Strobe lighting can trigger seizures in photosensitive epilepsyPhotosensitive epilepsy
Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns.-Symptoms:...
. An infamous event took place in 1997 in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
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. 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
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
of 10 Hz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
, 65% of affected people are still at risk. The British Health and Safety Executive
Health and Safety Executive
The Health and Safety Executive is a non-departmental public body in the United Kingdom. It is the body responsible for the encouragement, regulation and enforcement of workplace health, safety and welfare, and for research into occupational risks in England and Wales and Scotland...
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.
See also
- ElectrotachyscopeElectrotachyscopeThe électrotachyscope is an 1887 invention of Ottomar Anschütz of Germany which presents the illusion of motion with transparent serial photographs, chronophotographs, arranged on a spinning wheel of fortune or mandala-like glass disc, significant as a technological development in the history of...
- Flip bookFlip bookA flip book or flick book is a book with a series of pictures that vary gradually from one page to the next, so that when the pages are turned rapidly, the pictures appear to animate by simulating motion or some other change. Flip books are often illustrated books for children, but may also be...
- PhenakistoscopePhenakistoscopeThe phenakistoscope was an early animation device that used the persistence of vision principle to create an illusion of motion.-History:...
- PraxinoscopePraxinoscopeThe praxinoscope was an animation device, the successor to the zoetrope. It was invented in France in 1877 by Charles-Émile Reynaud. Like the zoetrope, it used a strip of pictures placed around the inner surface of a spinning cylinder...
- TachometerTachometerA tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
- ThaumatropeThaumatropeA thaumatrope is a toy that was popular in Victorian times.A disk or card with a picture on each side is attached to two pieces of string. When the strings are twirled quickly between the fingers the two pictures appear to combine into a single image due to persistence of vision.The invention of...
- ZoetropeZoetropeA zoetrope is a device that produces an illusion of action from a rapid succession of static pictures. The term zoetrope is from the Greek words "ζωή – zoe", "life" and τρόπος – tropos, "turn". It may be taken to mean "wheel of life"....
- JerkinessJerkinessJerkiness, sometimes called strobing, describes the perception of individual still images in a motion picture.Motion pictures are made from still images shown in rapid sequence...
, discontinuity in motion pictures, also called strobing - Photographic flashFlash (photography)A flash is a device used in photography producing a flash of artificial light at a color temperature of about 5500 K 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...
, often referred to as a strobe light - Strobing (dance form)