A report on Light

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
The electromagnetic spectrum, with the visible portion highlighted
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Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily
Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.
Hong Kong illuminated by colourful artificial lighting.
Pierre Gassendi.
Christiaan Huygens.
Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.
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Electromagnetic radiation within the portion of the electromagnetic spectrum that is perceived by the human eye.

- Light
A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

81 related topics with Alpha

Overall

The Lorentz factor γ as a function of velocity. It starts at1 and approaches infinity as v approaches c.

Speed of light

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Universal physical constant that is important in many areas of physics.

Universal physical constant that is important in many areas of physics.

The Lorentz factor γ as a function of velocity. It starts at1 and approaches infinity as v approaches c.
Event A precedes B in the red frame, is simultaneous with B in the green frame, and follows B in the blue frame.
The blue dot moves at the speed of the ripples, the phase velocity; the green dot moves with the speed of the envelope, the group velocity; and the red dot moves with the speed of the foremost part of the pulse, the front velocity.
A beam of light is depicted travelling between the Earth and the Moon in the time it takes a light pulse to move between them: 1.255 seconds at their mean orbital (surface-to-surface) distance. The relative sizes and separation of the Earth–Moon system are shown to scale.
Measurement of the speed of light using the eclipse of Io by Jupiter
Aberration of light: light from a distant source appears to be from a different location for a moving telescope due to the finite speed of light.
One of the last and most accurate time of flight measurements, Michelson, Pease and Pearson's 1930–35 experiment used a rotating mirror and a one-mile (1.6 km) long vacuum chamber which the light beam traversed 10 times. It achieved accuracy of ±11 km/s.
Diagram of the Fizeau apparatus
Electromagnetic standing waves in a cavity
An interferometric determination of length. Left: constructive interference; Right: destructive interference.
Rømer's observations of the occultations of Io from Earth
Hendrik Lorentz (right) with Albert Einstein

All forms of electromagnetic radiation, including visible light, travel at the speed of light.

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Optics

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The Nimrud lens
Alhazen (Ibn al-Haytham), "the father of Optics"
Reproduction of a page of Ibn Sahl's manuscript showing his knowledge of the law of refraction.
The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)
Cover of the first edition of Newton's Opticks (1704)
Geometry of reflection and refraction of light rays
Diagram of specular reflection
Illustration of Snell's Law for the case n1 < n2, such as air/water interface
A ray tracing diagram for a converging lens.
Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.
When oil or fuel is spilled, colourful patterns are formed by thin-film interference.
Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.
Dispersion: two sinusoids propagating at different speeds make a moving interference pattern. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this case, the phase velocity is twice the group velocity. The red dot overtakes two green dots, when moving from the left to the right of the figure. In effect, the individual waves (which travel with the phase velocity) escape from the wave packet (which travels with the group velocity).
Linear polarization diagram
Circular polarization diagram
Elliptical polarization diagram
A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.
The effects of a polarising filter on the sky in a photograph. Left picture is taken without polariser. For the right picture, filter was adjusted to eliminate certain polarizations of the scattered blue light from the sky.
Experiments such as this one with high-power lasers are part of the modern optics research.
VLT's laser guide star
Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina
The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.
Illustrations of various optical instruments from the 1728 Cyclopaedia
Photograph taken with aperture 32
Photograph taken with aperture 5
A colourful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers

Laser

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Red (660 & 635 nm), green (532 & 520 nm) and blue-violet (445 & 405 nm) lasers
A laser beam used for welding
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A helium–neon laser demonstration. The glow running through the center of the tube is an electric discharge. This glowing plasma is the gain medium for the laser. The laser produces a tiny, intense spot on the screen to the right. The center of the spot appears white because the image is overexposed there.
Spectrum of a helium–neon laser. The actual bandwidth is much narrower than shown; the spectrum is limited by the measuring apparatus.
Lidar measurements of lunar topography made by Clementine mission.
Laserlink point to point optical wireless network
Mercury Laser Altimeter (MLA) of the MESSENGER spacecraft
Aleksandr Prokhorov
Charles H. Townes
LASER notebook: First page of the notebook wherein Gordon Gould coined the acronym LASER, and described the elements required to construct one. Manuscript text: "Some rough calculations on the feasibility / of a LASER: Light Amplification by Stimulated / Emission of Radiation. /
Conceive a tube terminated by optically flat / [Sketch of a tube] / partially reflecting parallel mirrors..."
Graph showing the history of maximum laser pulse intensity throughout the past 40 years.
Wavelengths of commercially available lasers. Laser types with distinct laser lines are shown above the wavelength bar, while below are shown lasers that can emit in a wavelength range. The color codifies the type of laser material (see the figure description for more details).
A 50 W FASOR, based on a Nd:YAG laser, used at the Starfire Optical Range
A 5.6 mm 'closed can' commercial laser diode, such as those used in a CD or DVD player
Close-up of a table-top dye laser based on Rhodamine 6G
The free-electron laser FELIX at the FOM Institute for Plasma Physics Rijnhuizen, Nieuwegein
Lasers range in size from microscopic diode lasers (top) with numerous applications, to football field sized neodymium glass lasers (bottom) used for inertial confinement fusion, nuclear weapons research and other high energy density physics experiments.
The US–Israeli Tactical High Energy weapon has been used to shoot down rockets and artillery shells.
Laser application in astronomical adaptive optics imaging

A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Fluorescent minerals emit visible light when exposed to ultraviolet light.

Fluorescence

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Fluorescent minerals emit visible light when exposed to ultraviolet light.
Fluorescent marine organisms
Fluorescent clothes used in black light theater production, Prague
Lignum nephriticum cup made from the wood of the narra tree (Pterocarpus indicus), and a flask containing its fluorescent solution
Matlaline, the fluorescent substance in the wood of the tree Eysenhardtia polystachya
Jablonski diagram. After an electron absorbs a high-energy photon the system is excited electronically and vibrationally. The system relaxes vibrationally, and eventually fluoresces at a longer wavelength.
Fluorescent security strip in a US twenty dollar bill under UV light
Fluorescent coral
Fluorescence has multiple origins in the tree of life. This diagram displays the origins within actinopterygians (ray finned fish).
Fluorescent marine fish
Aequoria victoria, biofluorescent jellyfish known for GFP
Fluorescent polka-dot tree frog under UV-light
Fluorescing scorpion
Fluorescence of aragonite
Fluorescent paint and plastic lit by UV tubes. Paintings by Beo Beyond
Endothelial cells under the microscope with three separate channels marking specific cellular components

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.

Various examples of physical phenomena

Physics

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Natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force.

Natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force.

Various examples of physical phenomena
Ancient Egyptian astronomy is evident in monuments like the ceiling of Senemut's tomb from the Eighteenth Dynasty of Egypt.
Ibn al-Haytham (c. 965–c. 1040), Book of Optics Book I, [6.85], [6.86]. Book II, [3.80] describes his camera obscura experiments.
The basic way a pinhole camera works
Galileo Galilei showed a modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics.
Sir Isaac Newton (1643–1727), whose laws of motion and universal gravitation were major milestones in classical physics
Max Planck (1858–1947), the originator of the theory of quantum mechanics
Albert Einstein (1879–1955), whose work on the photoelectric effect and the theory of relativity led to a revolution in 20th century physics
The basic domains of physics
Solvay Conference of 1927, with prominent physicists such as Albert Einstein, Werner Heisenberg, Max Planck, Hendrik Lorentz, Niels Bohr, Marie Curie, Erwin Schrödinger and Paul Dirac
This parabola-shaped lava flow illustrates the application of mathematics in physics—in this case, Galileo's law of falling bodies.
Mathematics and ontology are used in physics. Physics is used in chemistry and cosmology.
The distinction between mathematics and physics is clear-cut, but not always obvious, especially in mathematical physics.
Classical physics implemented in an acoustic engineering model of sound reflecting from an acoustic diffuser
Archimedes' screw, a simple machine for lifting
Experiment using a laser
The astronaut and Earth are both in free fall.
Lightning is an electric current.
Physics involves modeling the natural world with theory, usually quantitative. Here, the path of a particle is modeled with the mathematics of calculus to explain its behavior: the purview of the branch of physics known as mechanics.
A simulated event in the CMS detector of the Large Hadron Collider, featuring a possible appearance of the Higgs boson.
Velocity-distribution data of a gas of rubidium atoms, confirming the discovery of a new phase of matter, the Bose–Einstein condensate
The deepest visible-light image of the universe, the Hubble Ultra-Deep Field
Feynman diagram signed by R. P. Feynman.
A typical phenomenon described by physics: a magnet levitating above a superconductor demonstrates the Meissner effect.

Optics, the study of light, is concerned not only with visible light but also with infrared and ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion, and polarization of light.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz

Frequency

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Number of occurrences of a repeating event per unit of time.

Number of occurrences of a repeating event per unit of time.

A pendulum making 25 complete oscillations in 60 s, a frequency of 0.41 Hertz
A pendulum with a period of 2.8 s and a frequency of 0.36 Hz
Diagram of the relationship between the different types of frequency and other wave properties.
Modern frequency counter
Complete spectrum of electromagnetic radiation with the visible portion highlighted
The sound wave spectrum, with rough guide of some applications

Frequency is an important parameter used in science and engineering to specify the temporal rate of change observed in oscillatory and periodic phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

Hydrogen atomic orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.

Electron

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Subatomic particle whose electric charge is negative one elementary charge.

Subatomic particle whose electric charge is negative one elementary charge.

Hydrogen atomic orbitals at different energy levels. The more opaque areas are where one is most likely to find an electron at any given time.
A beam of electrons deflected in a circle by a magnetic field
J. J. Thomson
Robert Millikan
The Bohr model of the atom, showing states of an electron with energy quantized by the number n. An electron dropping to a lower orbit emits a photon equal to the energy difference between the orbits.
In quantum mechanics, the behavior of an electron in an atom is described by an orbital, which is a probability distribution rather than an orbit. In the figure, the shading indicates the relative probability to "find" the electron, having the energy corresponding to the given quantum numbers, at that point.
Standard Model of elementary particles. The electron (symbol e) is on the left.
Example of an antisymmetric wave function for a quantum state of two identical fermions in a 1-dimensional box. If the particles swap position, the wave function inverts its sign.
A schematic depiction of virtual electron–positron pairs appearing at random near an electron (at lower left)
A particle with charge q (at left) is moving with velocity v through a magnetic field B that is oriented toward the viewer. For an electron, q is negative so it follows a curved trajectory toward the top.
Here, Bremsstrahlung is produced by an electron e deflected by the electric field of an atomic nucleus. The energy change E2 − E1 determines the frequency f of the emitted photon.
Probability densities for the first few hydrogen atom orbitals, seen in cross-section. The energy level of a bound electron determines the orbital it occupies, and the color reflects the probability of finding the electron at a given position.
A lightning discharge consists primarily of a flow of electrons. The electric potential needed for lightning can be generated by a triboelectric effect.
Lorentz factor as a function of velocity. It starts at value 1 and goes to infinity as v approaches c.
Pair production of an electron and positron, caused by the close approach of a photon with an atomic nucleus. The lightning symbol represents an exchange of a virtual photon, thus an electric force acts. The angle between the particles is very small.
An extended air shower generated by an energetic cosmic ray striking the Earth's atmosphere
Aurorae are mostly caused by energetic electrons precipitating into the atmosphere.
During a NASA wind tunnel test, a model of the Space Shuttle is targeted by a beam of electrons, simulating the effect of ionizing gases during re-entry.

In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as a de Broglie wave in the manner of light.

Circular polarization on rubber thread, converted to linear polarization

Polarization (waves)

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Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Property applying to transverse waves that specifies the geometrical orientation of the oscillations.

Circular polarization on rubber thread, converted to linear polarization
cross linear polarized
A "vertically polarized" electromagnetic wave of wavelength λ has its electric field vector E (red) oscillating in the vertical direction. The magnetic field B (or H) is always at right angles to it (blue), and both are perpendicular to the direction of propagation (z).
Electric field oscillation
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Animation showing four different polarization states and three orthogonal projections.
A circularly polarized wave as a sum of two linearly polarized components 90° out of phase
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Color pattern of a plastic box showing stress-induced birefringence when placed in between two crossed polarizers.
Paths taken by vectors in the Poincaré sphere under birefringence. The propagation modes (rotation axes) are shown with red, blue, and yellow lines, the initial vectors by thick black lines, and the paths they take by colored ellipses (which represent circles in three dimensions).
A stack of plates at Brewster's angle to a beam reflects off a fraction of the s-polarized light at each surface, leaving (after many such plates) a mainly p-polarized beam.
Stress in plastic glasses
Photomicrograph of a volcanic sand grain; upper picture is plane-polarized light, bottom picture is cross-polarized light, scale box at left-center is 0.25 millimeter.
Effect of a polarizer on reflection from mud flats. In the picture on the left, the horizontally oriented polarizer preferentially transmits those reflections; rotating the polarizer by 90° (right) as one would view using polarized sunglasses blocks almost all specularly reflected sunlight.
One can test whether sunglasses are polarized by looking through two pairs, with one perpendicular to the other. If both are polarized, all light will be blocked.
The effects of a polarizing filter (right image) on the sky in a photograph
Colored fringes in the Embassy Gardens Sky Pool when viewed through a polarizer, due to stress-induced birefringence in the skylight
Circular polarization through an airplane plastic window, 1989

Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves (shear waves) in solids.

Thomas Young's sketch of two-slit diffraction of waves, 1803

Wave–particle duality

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Concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave.

Concept in quantum mechanics that every particle or quantum entity may be described as either a particle or a wave.

Thomas Young's sketch of two-slit diffraction of waves, 1803
The photoelectric effect. Incoming photons on the left strike a metal plate (bottom), and eject electrons, depicted as flying off to the right.
Propagation of de Broglie waves in 1d—real part of the complex amplitude is blue, imaginary part is green. The probability (shown as the colour opacity) of finding the particle at a given point x is spread out like a waveform; there is no definite position of the particle. As the amplitude increases above zero the curvature decreases, so the amplitude decreases again, and vice versa—the result is an alternating amplitude: a wave. Top: Plane wave. Bottom: Wave packet.
Couder experiments, "materializing" the pilot wave model
Particle impacts make visible the interference pattern of waves.
A quantum particle is represented by a wave packet.
Interference of a quantum particle with itself.

Democritus (5th century BC) argued that all things in the universe, including light, are composed of indivisible sub-components.

Blue, green, and red LEDs in 5 mm diffused cases

Light-emitting diode

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Blue, green, and red LEDs in 5 mm diffused cases
Parts of a conventional LED. The flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out via mechanical strain or vibration.
Close-up image of a surface mount LED
A bulb-shaped modern retrofit LED lamp with aluminum heat sink, a light diffusing dome and E27 screw base, using a built-in power supply working on mains voltage
Green electroluminescence from a point contact on a crystal of SiC recreates Round's original experiment from 1907.
A 1962 Texas Instruments SNX-100 GaAs LED contained in a TO-18 transistor metal case
LED display of a TI-30 scientific calculator (ca. 1978), which uses plastic lenses to increase the visible digit size
X-Ray of a 1970s 8-digit LED calculator display
Illustration of Haitz's law, showing improvement in light output per LED over time, with a logarithmic scale on the vertical axis
Blue LEDs
Combined spectral curves for blue, yellow-green, and high-brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24–27 nm for all three colors.
RGB LED
Spectrum of a white LED showing blue light directly emitted by the GaN-based LED (peak at about 465 nm) and the more broadband Stokes-shifted light emitted by the Ce3+:YAG phosphor, which emits at roughly 500–700 nm
LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have colorless housings. Modern high-power LEDs such as those used for lighting and backlighting are generally found in surface-mount technology (SMT) packages (not shown).
Image of miniature surface mount LEDs in most common sizes. They can be much smaller than a traditional 5mm lamp type LED, shown on the upper left corner.
Very small (1.6×1.6×0.35mm) red, green, and blue surface mount miniature LED package with gold wire bonding details.
High-power light-emitting diodes attached to an LED star base (Luxeon, Lumileds)
RGB-SMD-LED
Composite image of an 11 × 44 LED matrix lapel name tag display using 1608/0603-type SMD LEDs. Top: A little over half of the 21 × 86 mm display. Center: Close-up of LEDs in ambient light. Bottom: LEDs in their own red light.
Simple LED circuit with resistor for current limiting
Daytime running light LEDs of an automobile
Red and green LED traffic signals
LED for miners, to increase visibility inside mines
Los Angeles Vincent Thomas Bridge illuminated with blue LEDs
LED costume for stage performers
LED wallpaper by Meystyle
A large LED display behind a disc jockey
Seven-segment display that can display four digits and points
LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it.