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A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of
light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
. It is one of a number of devices that can be used as a
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. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces br ...
. The word originated from the
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
('), meaning "act of whirling". A typical commercial strobe light has a flash energy in the region of 10 to 150
joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s, and discharge times as short as a few milliseconds, often resulting in a flash power of several
kilowatt The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wa ...
s. Larger strobe lights can be used in “continuous” mode, producing extremely intense illumination. The light source is commonly a
xenon flash lamp A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
, or ''flashtube'', which has a complex
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
and a
color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
of approximately 5,600
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
s. To obtain colored light, colored gels may be used.


Scientific explanation of flashtubes

Strobe lights usually use
flashtube A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
s with energy supplied from a
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
, an energy storage device much like a battery, but capable of charging and releasing energy much faster. In a capacitor-based strobe, the capacitor is charged up to around 300 V. Once the capacitor has been charged, to trigger the flash a small amount of power is diverted into a
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 Trigger transformer cores may be utilized in a un ...
, a small transformer with a high turns ratio. This generates the 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 path for the capacitor to discharge through, allowing the capacitor to quickly release its energy into the arc. The capacitor's energy 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 type of strobe requires no charging time and allows for much quicker flash rates, but drastically reduces the lifetime of the flash tube if powered for significant periods of time. Such strobes require a form of
current limiting Current limiting is the practice of imposing a limit on the current that may be delivered to a load to protect the circuit generating or transmitting the current from harmful effects due to a short-circuit or overload. The term "current limiting" i ...
, without which the flash tube would attempt to draw high currents from the electricity source, potentially tripping electrical breakers or causing
voltage drop Voltage drop is the decrease of electrical potential along the path of a current flowing in an electrical circuit. Voltage drops in the internal resistance of the source, across conductors, across contacts, and across connectors are undesirable ...
s in the power supply line. The duration of a single flash depends on the particular strobe being used and its settings. Strobes for studio lighting often have a range of power settings. For a given strobe, higher light output corresponds to a longer flash duration. For example, the Flashpoint Rapid 1200 HSS Monolight has a flash duration as long as 5.6 ms (1/180 sec) at its highest output setting, or as short as 68 μs (1/14,814 sec) at its lowest output setting. Strobes with significantly shorter flash durations are commercially available, some with flash durations less than 1 μs. For example, the SPOT strobe by Prism Science Works provides a flash duration of order 0.5 μs Some strobes even offer continuous mode of operation whereby the arc is sustained, providing extremely high intensity light, but usually only for small amounts of time to prevent overheating and eventual breakage of the flash tube.


Applications


Strobe beacons

A strobe
beacon A beacon is an intentionally conspicuous device designed to attract attention to a specific location. A common example is the lighthouse, which draws attention to a fixed point that can be used to navigate around obstacles or into port. More mode ...
is a flashing electric
lamp Lamp, Lamps or LAMP may refer to: Lighting * Oil lamp, using an oil-based fuel source * Kerosene lamp, using kerosene as a fuel * Electric lamp, or light bulb, a replaceable component that produces light from electricity * Light fixture, or li ...
used in a variety of industries as an
attention Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Atte ...
-getting device, either to warn of possible
hazard A hazard is a potential source of harm Harm is a moral and legal concept. Bernard Gert construes harm as any of the following: * pain * death * disability * mortality * loss of abil ity or freedom * loss of pleasure. Joel Feinberg giv ...
s, or to attract potential
customer In sales, commerce, and economics, a customer (sometimes known as a client, buyer, or purchaser) is the recipient of a good, service, product or an idea - obtained from a seller, vendor, or supplier via a financial transaction or exchange for ...
s. Strobe beacons are similar to rotating beacons, but are more energy efficient, and with no moving parts, are more reliable and less likely to break. Gas strobe beacons include
Xenon flash lamp A flashtube (flashlamp) is an electric arc lamp designed to produce extremely intense, incoherent, full-spectrum white light for a very short time. A flashtube is a glass tube with an electrode at each end and is filled with a gas that, when tr ...
and
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
varieties. Gas strobe beacons consist of a gas-filled
tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * ''The Tube'' (TV series), a music related TV series by Channel 4 in the United Kingdom * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a ...
surrounded by a
lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...
. When
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
is applied, the tube flashes, is magnified by the lens, and a 360 degree light is emitted. The intensity of the light depends on the amount of electricity provided. These lenses come in a variant of colors, mainly, Clear, Yellow, Amber, Red, Blue, and Green. The lens color can affect the intensity of light.
LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
strobe beacons consist of a base, a LED or group of LEDs, and a cover. A solid state flash controller is located within the base, which allows the LED beacon to operate in a variety of flash patterns. Strobe lights are often used for aircraft anti-collision lighting both on aircraft themselves and also on tall stationary objects, such as television and radio towers. Other applications are in
alarm system An alarm device is a mechanism that gives an audible, visual or other kind of alarm signal to alert someone to a problem or condition that requires urgent attention. Alphabetical musical instruments Etymology The word ''alarm'' comes from th ...
s,
emergency vehicle lighting Emergency vehicle lighting, also known as simply emergency lighting or emergency lights, is a type of vehicle lighting used to visually announce a vehicle's presence to other road users. A sub-type of emergency vehicle equipment, emergency veh ...
,
theatrical Theatre or theater is a collaborative form of performing art that uses live performers, usually actor, actors or actresses, to present the experience of a real or imagined event before a live audience in a specific place, often a stage. The p ...
lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing daylig ...
(most notably to simulate
lightning Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
), and as high-visibility aircraft collision avoidance lights. They are still widely used in law enforcement and other emergency vehicles, though they are slowly being replaced by
LED A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
technology in this application, as they themselves largely replaced
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...
lighting. Strobes are used by
scuba diver Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for "Self-Contained Underwater Breathing Apparatus", was coined by Chris ...
s as an emergency signaling device.


Stroboscopic effect

Special calibrated strobe lights, capable of flashing up to hundreds of times per second, are used in industry to stop the appearance of 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 an even multiple, i.e. 2*π*n/ω, where n is an integer and ω the
angular frequency In physics, angular frequency "''ω''" (also referred to by the terms angular speed, circular frequency, orbital frequency, radian frequency, and pulsatance) is a scalar measure of rotation rate. It refers to the angular displacement per unit tim ...
), 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. A common use of a strobe flash is to optimize a
car engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combust ...
's efficiency at a certain rotational period by directing the strobe-light towards a mark on the
flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...
on the engine's main
axle An axle or axletree 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 the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
. The strobe-light tool for such
ignition timing In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for ...
is called a
timing light A timing light is a stroboscope used to dynamically set the ignition timing of an Otto cycle or similar internal combustion engine equipped with a distributor. Modern electronically controlled passenger vehicle engines require use of a scan tool ...
. 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.


Other

Strobelights are often used to give an illusion of slow motion in
nightclub A nightclub (music club, discothèque, disco club, or simply club) is an entertainment venue during nighttime comprising a dance floor, lightshow, and a stage for live music or a disc jockey (DJ) who plays recorded music. Nightclubs gener ...
s and
rave A rave (from the verb: '' to rave'') is a dance party at a warehouse, club, or other public or private venue, typically featuring performances by DJs playing electronic dance music. The style is most associated with the early 1990s dance mus ...
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" Edgerton employed a flashing lamp to make an improved
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. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces br ...
for the study of moving objects, eventually resulting in dramatic
photographs A photograph (also known as a photo, image, or picture) is an image created by light falling on a photosensitive surface, usually photographic film or an electronic image sensor, such as a CCD or a CMOS chip. Most photographs are now created ...
of objects such as bullets in flight.
EG&G EG&G, formally known as Edgerton, Germeshausen, and Grier, Inc., was a United States national defense contractor and provider of management and technical services. The company was involved in contracting services to the United States government ...
URS Urs (from ''‘Urs'') or ''Urus'' (literal meaning wedding), is the death anniversary of a Sufi saint, usually held at the saint's dargah (shrine or tomb). In most Sufi orders such as Naqshbandiyyah, Suhrawardiyya, Chishtiyya, Qadiriyya, etc ...
''] 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 The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
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.
Internally triggered ''Strobotrons'' (light-output optimized
thyratron A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, pro ...
s) were available as well as flood beam CRT-type, grid-controlled ''Vacuum stroboscopic light sources'' with fast
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or vi ...
s. The strobe light was popularized on the club scene during the 1960s when it was used to reproduce and enhance the effects of
LSD Lysergic acid diethylamide (LSD), also known colloquially as acid, is a potent psychedelic drug. Effects typically include intensified thoughts, emotions, and sensory perception. At sufficiently high dosages LSD manifests primarily mental, vi ...
trips.
Ken Kesey Ken Elton Kesey (September 17, 1935 – November 10, 2001) was an American novelist, essayist and countercultural figure. He considered himself a link between the Beat Generation of the 1950s and the hippies of the 1960s. Kesey was born in ...
used strobe lighting in coordination with the music of the
Grateful Dead The Grateful Dead was an American rock music, rock band formed in 1965 in Palo Alto, California. The band is known for its eclectic style, which fused elements of rock, Folk music, folk, country music, country, jazz, bluegrass music, bluegrass, ...
during his
Acid Tests The Acid Tests were a series of parties held by author Ken Kesey primarily in the San Francisco Bay Area during the mid-1960s, centered on the use of and advocacy for the psychedelic drug LSD, commonly known as "acid". LSD was not made illegal ...
. In early 1966,
Andy Warhol Andy Warhol (; born Andrew Warhola Jr.; August 6, 1928 – February 22, 1987) was an American visual artist, film director, and producer who was a leading figure in the visual art movement known as pop art. His works explore the relationsh ...
's lights engineer, Danny Williams, pioneered the use of multiple stroboscopes, slides and film projections simultaneously onstage during the 1966
Exploding Plastic Inevitable The ''Exploding Plastic Inevitable'', sometimes simply called ''Plastic Inevitable'' or ''EPI'', was a series of multimedia events organized by Andy Warhol in 1966 and 1967, featuring musical performances by The Velvet Underground & Nico, screenin ...
shows, and at Bill Graham's request, Williams built an enhanced stroboscopic light show to be used at
Fillmore West The Fillmore West was a historic rock and roll music venue in San Francisco, California, US which became famous under the direction of concert promoter Bill Graham from 1968 to 1971. Named after The Fillmore at the intersection of Fillmore Str ...
.


Fechner color

Rapid flashing of a stroboscopic light can give the illusion that white light is tinged with color, known as Fechner color. Within certain ranges, the apparent color can be controlled by the frequency of the flash. Effective stimuli frequencies go from 3 Hz upwards, with optimal frequencies of about 4–6 Hz. The colours are an illusion generated in the mind of the observer and not a real color. The Benham's top demonstrates the effect.    


Strobe lights and epilepsy

Sometimes strobe lighting can trigger
seizures An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or neural oscillation, synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much o ...
in
photosensitive epilepsy Photosensitive epilepsy (PSE) 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. PSE affects approximately o ...
. An infamous event took place in 1997 in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
when an episode of the ''Pokémon'' anime, "
Dennō Senshi Porygon is the 38th episode of the ''Pokémon'' anime's first season. Its sole broadcast was in Japan on December 16, 1997. In the episode, Ash and his friends find at the local Pokémon Center that there is something wrong with the Poké Ball transm ...
" (commonly translated as "Electric Soldier Porygon"), featured a scene that depicted a huge explosion using extremely bright flashing red and blue lights with a strobe effect at about 12 Hz, causing about 685 of the viewing children to be sent to hospitals. Although 95% of the 685 just complained of dizziness, some were hospitalized. Organizers later said that they did not know about the threshold of strobing. Most strobe lights on sale to the public are factory-limited to about 10–12 Hz (10–12 flashes per second) in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. Studies have shown that the majority of people that are susceptible to the strobing effects can have symptoms, albeit rarely, at 15 Hz-70 Hz. Other studies have shown epileptic symptoms at the 15 Hz rate with over 90 seconds of continuous staring at a strobe light. Many
fire alarms A fire alarm system warns people when smoke, fire, carbon monoxide or other fire-related or general notification emergency, emergencies are detected. These alarms may be activated automatically from smoke detectors and heat detectors or may also ...
in schools, hospitals, stadiums, etc. strobe at a 1 Hz rate.


See also

*
Electrotachyscope The Elektrischen Schnellseher (literally "Electrical Quick-Viewer") or Electrotachyscope was an early motion picture system developed by chronophotographer Ottomar Anschütz between 1886 and 1894. He made at least seven different versions of the ma ...
, an early motion picture system in limited use between 1886 and 1894. *
Emergency vehicle lighting Emergency vehicle lighting, also known as simply emergency lighting or emergency lights, is a type of vehicle lighting used to visually announce a vehicle's presence to other road users. A sub-type of emergency vehicle equipment, emergency veh ...
*
Flicker (light) In visual perception, flicker is a human-visible change in luminous flux of an illuminated surface or light source which can be due to fluctuations of the light source itself, or due to external causes such as due to rapid fluctuations in the volta ...
, the study of directly visible change in brightness of a light source *
Flicker fusion threshold The flicker fusion threshold, critical flicker frequency (CFF) or flicker fusion rate, is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the avera ...
, the frequency at which an intermittent light stimulus appears to be completely steady to the average human observer *
Tachometer A tachometer (revolution-counter, tach, rev-counter, RPM gauge) 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 (RPM) on a calibrated anal ...
, an instrument measuring the rotation speed of a shaft or disk, *
Zoetrope A zoetrope is one of several pre-film animation devices that produce the illusion of motion by displaying a sequence of drawings or photographs showing progressive phases of that motion. It was basically a cylindrical variation of the phénak ...
, an early device from 1813 that produced the illusion of motion by displaying a sequence of drawings or photographs showing progressive phases of that motion. *
Jerkiness Jerkiness, sometimes called strobing or choppy, describes the perception of individual still images in a motion picture. Motion pictures are made from still images shown in rapid sequence. Provided there is sufficient continuity between the imag ...
, discontinuity in motion pictures, also called strobing *
Photographic flash A flash is a device used in photography that produces a brief burst of light (typically lasting 1/1000 to 1/200 of a second) at a color temperature of about 5500  K to help illuminate a scene. A major purpose of a flash is to illuminate a ...
, often also referred to as a strobe light *
Wagon-wheel effect The wagon-wheel effect (alternatively called stagecoach-wheel effect or stroboscopic effect) is an optical illusion in which a spoked wheel appears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the ...
, an
optical illusion Within visual perception, an optical illusion (also called a visual illusion) is an illusion caused by the visual system and characterized by a visual perception, percept that arguably appears to differ from reality. Illusions come in a wide v ...
in cinematography which a spoked
wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...
appears to rotate differently from its true rotation *
Air-gap flash An air-gap flash is a photographic light source capable of producing sub-microsecond light flashes, allowing for (ultra) high-speed photography. This is achieved by a high-voltage (20 kV typically) electric discharge between two electrodes o ...
, a photographic light source capable of producing sub-microsecond light flashes, allowing for (ultra)
high-speed photography High-speed photography is the science of taking pictures of very fast phenomena. In 1948, the Society of Motion Picture and Television Engineers (SMPTE) defined high-speed photography as any set of photographs captured by a camera capable of 69 ...


References

{{Artificial light sources Gas discharge lamps History of animation 1938 introductions Devices to alter consciousness