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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 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 ...
which produces brief repetitive flashes of light. Usually, the rate of the stroboscope is adjustable to different frequencies. When a rotating or vibrating object is observed with the stroboscope at its vibration frequency (or a submultiple of it), it appears stationary. Thus stroboscopes are also used to measure frequency. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating string are common examples. A stroboscope used to set the
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 f ...
of
internal combustion 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 co ...
s is called a timing light.


Mechanical

In its simplest mechanical form, a stroboscope can be a rotating cylinder (or bowl with a raised edge) with evenly spaced holes or slots placed in the line of sight between the observer and the moving object. The observer looks through the holes/slots on the near and far side at the same time, with the slots/holes moving in opposite directions. When the holes/slots are aligned on opposite sides, the object is visible to the observer. Alternately, a single moving hole or slot can be used with a fixed/stationary hole or slot. The stationary hole or slot limits the light to a single viewing path and reduces glare from light passing through other parts of the moving hole/slot. Viewing through a single line of holes/slots does not work, since the holes/slots appear to just sweep across the object without a strobe effect. The rotational speed is adjusted so that it becomes synchronised with the movement of the observed system, which seems to slow and stop. The illusion is caused by temporal
aliasing In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or ''aliases'' of one another) when sampled. It also often refers to the distortion or artifact that results when ...
, commonly known as the
stroboscopic effect The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous rotational or other cyclic motion is represented by a series of short or instantaneous samples (as opposed to a continuous view) at a sampling rate c ...
.


Electronic

In electronic versions, the perforated disc is replaced by a
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 ligh ...
capable of emitting brief and rapid flashes of light. Typically a gas-discharge or solid-state lamp is used, because they are capable of emitting light nearly instantly when power is applied, and extinguishing just as fast when the power is removed. By comparison,
incandescent lamp An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxida ...
s have a brief warm-up when energized, followed by a cool-down period when power is removed. These delays result in smearing and blurring of detail of objects partially illuminated during the warm-up and cool-down periods. For most applications, incandescent lamps are too slow for clear stroboscopic effects. Yet when operated from an AC source they are mostly fast enough to cause audible hum (at double mains frequency) on optical audio playback such as on film projection. The
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
of the flash is adjusted so that it is an equal to, or a unit fraction of the object's cyclic speed, at which point the object is seen to be either stationary or moving slowly backward or forward, depending on the flash frequency.
Neon lamp A neon lamp (also neon glow lamp) is a miniature gas discharge lamp. The lamp typically consists of a small glass capsule that contains a mixture of neon and other gases at a low pressure and two electrodes (an anode and a cathode). When suff ...
s or
light-emitting diode 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 ...
s are commonly used for low-intensity strobe applications, Neon lamps were more common before the development of solid-state electronics, but are being replaced by LEDs in most low-intensity strobe applications.
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 ...
s are used for medium- and high-intensity strobe applications. Sufficiently rapid or bright flashing may require active cooling such as forced-air or water cooling to prevent the xenon flash lamp from melting.


History

Joseph Plateau Joseph Antoine Ferdinand Plateau (14 October 1801 – 15 September 1883) was a Belgian physicist and mathematician. He was one of the first people to demonstrate the illusion of a moving image. To do this, he used counterrotating disks with repe ...
of
Belgium Belgium, ; french: Belgique ; german: Belgien officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to ...
is generally credited with the invention of the stroboscope in 1832, when he used a disc with radial slits which he turned while viewing images on a separate rotating wheel. Plateau's device became known as the "
Phenakistoscope The phenakistiscope (also known by the spellings phénakisticope or phenakistoscope) was the first widespread animation device that created a fluent illusion of motion. Dubbed and ('stroboscopic discs') by its inventors, it has been known unde ...
". There was an almost simultaneous and independent invention of the device by the
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
n Simon Ritter von Stampfer, which he named the "Stroboscope", and it is his term which is used today. The etymology is from the Greek words ''στρόβος - strobos'', meaning "whirlpool" and ''σκοπεῖν - skopein'', meaning "to look at". As well as having important applications for scientific research, the earliest inventions received immediate popular success as methods for producing moving pictures, and the principle was used for numerous toys. Other early pioneers employed rotating mirrors, or vibrating mirrors known as mirror galvanometers. In 1917, French engineer Etienne Oehmichen patented the first electric stroboscope, building at the same time a camera capable of shooting 1,000 frames per second.
Harold Eugene Edgerton Harold Eugene "Doc" Edgerton (April 6, 1903 – January 4, 1990), also known as Papa Flash, was an American scientist and researcher, a professor of electrical engineering at the Massachusetts Institute of Technology. He is largely credited with ...
("Doc" Edgerton) employed a flashing lamp to study machine parts in motion.
General Radio Corporation General Radio Company (later, GenRad) was a broad-line manufacturer of electronic test equipment in Massachusetts, U.S. from 1915 to 2001. History On June 14, 1915, Melville Eastham and a small group of investors started General Radio Company ...
then went on to produce this device in the form of their "Strobotac", an early example of a commercially successful stroboscope. Edgerton later used very short flashes of light as a means of producing still
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 fast-moving objects, such as bullets in flight.


Applications

Stroboscopes play an important role in the study of stresses on machinery in motion, and in many other forms of research. Bright stroboscopes are able to overpower ambient lighting and make stop-motion effects apparent without the need for dark ambient operating conditions. They are also used as measuring instruments for determining cyclic speed. As a timing light they are used to set the
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 f ...
of
internal combustion 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 co ...
s. In medicine, stroboscopes are used to view the
vocal cords In humans, vocal cords, also known as vocal folds or voice reeds, are folds of throat tissues that are key in creating sounds through vocalization. The size of vocal cords affects the pitch of voice. Open when breathing and vibrating for speec ...
for the diagnosis of conditions that have produced
dysphonia A hoarse voice, also known as dysphonia or hoarseness, is when the voice involuntarily sounds breathy, raspy, or strained, or is softer in volume or lower in pitch. A hoarse voice, can be associated with a feeling of unease or scratchiness in the ...
(hoarseness). The patient hums or speaks into a
microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and publ ...
which in turn activates the stroboscope at either the same or a slightly different frequency. The light source and a camera are positioned by
endoscopy An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are inse ...
. Another application of the stroboscope can be seen on many
gramophone A phonograph, in its later forms also called a gramophone (as a trademark since 1887, as a generic name in the UK since 1910) or since the 1940s called a record player, or more recently a turntable, is a device for the mechanical and analogu ...
turntables. The edge of the platter has marks at specific intervals so that when viewed under fluorescent lighting powered at
mains frequency The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to th ...
, provided the platter is rotating at the correct speed, the marks appear to be stationary. This will not work well under
incandescent lighting An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated until it glows. The filament is enclosed in a glass bulb with a vacuum or inert gas to protect the filament from oxida ...
, as incandescent bulbs don't significantly strobe. For this reason, some turntables have a neon bulb or LED next to the platter. The LED must be driven by a half wave rectifier from the mains transformer, or by an oscillator. Flashing lamp strobes are also adapted for pop use, as a lighting effect for
discotheque 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 gene ...
s and
night club 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 where they give the impression of dancing in slow motion. The strobe rate of these devices is typically not very precise or very fast, because the entertainment application does not usually require a high degree of performance.


Fechner color

Rapid flashing of the stroboscopic light can give the illusion that white light is tinged with color, known as
Fechner color The Fechner color effect is an illusion of color seen when looking at certain rapidly changing or moving black-and-white patterns. They are also called pattern induced flicker colors (PIFCs). The effect is most commonly demonstrated with a device ...
. 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.


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 ...
*
Flip book A flip book, flipbook, flicker book, or kineograph is a booklet with a series of images that very gradually change from one page to the next, so that when the pages are viewed in quick succession, the images appear to animate by simulating moti ...
*
Reciprocating motion Reciprocating motion, also called reciprocation, is a repetitive up-and-down or back-and-forth linear motion. It is found in a wide range of mechanisms, including reciprocating engines and pumps. The two opposite motions that comprise a single r ...
*
Phenakistoscope The phenakistiscope (also known by the spellings phénakisticope or phenakistoscope) was the first widespread animation device that created a fluent illusion of motion. Dubbed and ('stroboscopic discs') by its inventors, it has been known unde ...
*
Praxinoscope The 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. The p ...
*
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. The word originated from the Ancient Greek ('), meaning ...
*
Strobe tuner In music, an electronic tuner is a device that detects and displays the pitch of musical notes played on a musical instrument. "Pitch" is the perceived fundamental frequency of a musical note, which is typically measured in Hertz. Simple tun ...
*
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 analo ...
*
Thaumatrope A thaumatrope is an optical toy that was popular in the 19th century. A disk 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 blend into one due t ...
*
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 ...


References


External links

*
Demonstration of Phenakistoscope and Stroboscope at North Carolina School of Science and Mathematics
{{Authority control Audiovisual introductions in 1832 Measuring instruments Medical equipment