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

Figure 1. Michelson and Morley's interferometric setup, mounted on a stone slab that floats in an annular trough of mercury

Michelson–Morley experiment

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Figure 1. Michelson and Morley's interferometric setup, mounted on a stone slab that floats in an annular trough of mercury
Figure 2. A depiction of the concept of the "aether wind"
Michelson's 1881 interferometer. Although ultimately it proved incapable of distinguishing between differing theories of aether-dragging, its construction provided important lessons for the design of Michelson and Morley's 1887 instrument.
Figure 5. This figure illustrates the folded light path used in the Michelson–Morley interferometer that enabled a path length of 11 m. a is the light source, an oil lamp. b is a beam splitter. c is a compensating plate so that both the reflected and transmitted beams travel through the same amount of glass (important since experiments were run with white light which has an extremely short coherence length requiring precise matching of optical path lengths for fringes to be visible; monochromatic sodium light was used only for initial alignment ). d, d' and e are mirrors. e'  is a fine adjustment mirror. f is a telescope.
Figure 6. Fringe pattern produced with a Michelson interferometer using white light. As configured here, the central fringe is white rather than black.
Figure 7. Michelson and Morley's results. The upper solid line is the curve for their observations at noon, and the lower solid line is that for their evening observations. Note that the theoretical curves and the observed curves are not plotted at the same scale: the dotted curves, in fact, represent only one-eighth of the theoretical displacements.
Expected differential phase shift between light traveling the longitudinal versus the transverse arms of the Michelson–Morley apparatus
Figure 8. Simulation of the Kennedy/Illingworth refinement of the Michelson–Morley experiment. (a) Michelson–Morley interference pattern in monochromatic mercury light, with a dark fringe precisely centered on the screen. (b) The fringes have been shifted to the left by 1/100 of the fringe spacing. It is extremely difficult to see any difference between this figure and the one above. (c) A small step in one mirror causes two views of the same fringes to be spaced 1/20 of the fringe spacing to the left and to the right of the step. (d) A telescope has been set to view only the central dark band around the mirror step. Note the symmetrical brightening about the center line. (e) The two sets of fringes have been shifted to the left by 1/100 of the fringe spacing. An abrupt discontinuity in luminosity is visible across the step.
Figure 9. Michelson–Morley experiment with cryogenic optical resonators of a form such as was used by Müller et al. (2003).
Figure 10. 7Li-NMR spectrum of LiCl (1M) in D2O. The sharp, unsplit NMR line of this isotope of lithium is evidence for the isotropy of mass and space.

The Michelson–Morley experiment was an attempt to detect the existence of the luminiferous aether, a supposed medium permeating space that was thought to be the carrier of light waves.

Gauss's law for magnetism: magnetic field lines never begin nor end but form loops or extend to infinity as shown here with the magnetic field due to a ring of current.

Maxwell's equations

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Maxwell's equations are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.

Maxwell's equations are a set of coupled partial differential equations that, together with the Lorentz force law, form the foundation of classical electromagnetism, classical optics, and electric circuits.

Gauss's law for magnetism: magnetic field lines never begin nor end but form loops or extend to infinity as shown here with the magnetic field due to a ring of current.
In a geomagnetic storm, a surge in the flux of charged particles temporarily alters Earth's magnetic field, which induces electric fields in Earth's atmosphere, thus causing surges in electrical power grids. (Not to scale.)
Magnetic-core memory (1954) is an application of Ampère's law. Each core stores one bit of data.
Left: A schematic view of how an assembly of microscopic dipoles produces opposite surface charges as shown at top and bottom. Right: How an assembly of microscopic current loops add together to produce a macroscopically circulating current loop. Inside the boundaries, the individual contributions tend to cancel, but at the boundaries no cancelation occurs.

The speed calculated for electromagnetic waves, which could be predicted from experiments on charges and currents, matches the speed of light; indeed, light is one form of electromagnetic radiation (as are X-rays, radio waves, and others).

The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.

Sunlight

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Portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

Portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

The Sun, as seen from low Earth orbit overlooking the International Space Station. This sunlight is not filtered by the lower atmosphere, which blocks much of the solar spectrum.
Sunrise over the Gulf of Mexico and Florida. Taken on 20 October 1968 from Apollo 7.
Sunlight on Mars is dimmer than on Earth. This photo of a Martian sunset was imaged by Mars Pathfinder.
Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber
Sunlight shining through clouds, giving rise to crepuscular rays
Spectrum of the visible wavelengths at approximately sea level; illumination by direct sunlight compared with direct sunlight scattered by cloud cover and with indirect sunlight by varying degrees of cloud cover. The yellow line shows the power spectrum of direct sunlight under optimal conditions. To aid comparison, the other illumination conditions are scaled by the factor shown in the key so they match at about 470 nm (blue light).
Sunlight penetrating through a forest canopy in Germany
Édouard Manet: Le déjeuner sur l'herbe (1862-63)
Téli verőfény ("Winter Sunshine") by László Mednyánszky, early 20th century
Sun bathers in Finland

When direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat.

A plasma lamp, using electrical energy to create plasma light, heat, movement and a faint sound

Energy

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A plasma lamp, using electrical energy to create plasma light, heat, movement and a faint sound
In a typical lightning strike, 500 megajoules of electric potential energy is converted into the same amount of energy in other forms, mostly light energy, sound energy and thermal energy.
Thermal energy is energy of microscopic constituents of matter, which may include both kinetic and potential energy.
Thomas Young, the first person to use the term "energy" in the modern sense.
Joule's apparatus for measuring the mechanical equivalent of heat. A descending weight attached to a string causes a paddle immersed in water to rotate.
Basic overview of energy and human life.
A turbo generator transforms the energy of pressurized steam into electrical energy

In physics, energy is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat and light.

A specially developed CCD in a wire-bonded package used for ultraviolet imaging

Charge-coupled device

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Integrated circuit containing an array of linked, or coupled, capacitors.

Integrated circuit containing an array of linked, or coupled, capacitors.

A specially developed CCD in a wire-bonded package used for ultraviolet imaging
George E. Smith and Willard Boyle, 2009
The charge packets (electrons, blue) are collected in potential wells (yellow) created by applying positive voltage at the gate electrodes (G). Applying positive voltage to the gate electrode in the correct sequence transfers the charge packets.
Sony ICX493AQA 10.14-megapixel APS-C (23.4 × 15.6 mm) CCD from digital camera Sony α DSLR-A200 or DSLR-A300, sensor side
CCD from a 2.1-megapixel Argus digital camera
One-dimensional CCD image sensor from a fax machine
A frame transfer CCD sensor
Electrons are transferred serially through the gain stages making up the multiplication register of an EMCCD. The high voltages used in these serial transfers induce the creation of additional charge carriers through impact ionisation.
in an EMCCD there is a dispersion (variation) in the number of electrons output by the multiplication register for a given (fixed) number of input electrons (shown in the legend on the right). The probability distribution for the number of output electrons is plotted logarithmically on the vertical axis for a simulation of a multiplication register. Also shown are results from the empirical fit equation shown on this page.
Array of 30 CCDs used on the Sloan Digital Sky Survey telescope imaging camera, an example of "drift-scanning".
A Bayer filter on a CCD
x80 microscope view of an RGGB Bayer filter on a 240 line Sony CCD PAL Camcorder CCD sensor
Vertical smear

An image is projected through a lens onto the capacitor array (the photoactive region), causing each capacitor to accumulate an electric charge proportional to the light intensity at that location.

The interference of two waves. When in phase, the two lower waves create constructive interference (left), resulting in a wave of greater amplitude. When 180° out of phase, they create destructive interference (right).

Wave interference

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Phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

Phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude.

The interference of two waves. When in phase, the two lower waves create constructive interference (left), resulting in a wave of greater amplitude. When 180° out of phase, they create destructive interference (right).
Interference of right traveling (green) and left traveling (blue) waves in Two-dimensional space, resulting in final (red) wave
Interference of waves from two point sources.
A magnified image of a coloured interference pattern in a soap film. The "black holes" are areas of almost total destructive interference (antiphase).
Geometrical arrangement for two plane wave interference
Interference fringes in overlapping plane waves
Optical interference between two point sources that have different wavelengths and separations of sources.
Creation of interference fringes by an optical flat on a reflective surface. Light rays from a monochromatic source pass through the glass and reflect off both the bottom surface of the flat and the supporting surface.  The tiny gap between the surfaces means the two reflected rays have different path lengths. In addition the ray reflected from the bottom plate undergoes a 180° phase reversal.  As a result, at locations (a) where the path difference is an odd multiple of λ/2, the waves reinforce.   At locations (b) where the path difference is an even multiple of λ/2 the waves cancel.  Since the gap between the surfaces varies slightly in width at different points, a series of alternating bright and dark bands, interference fringes, are seen.
White light interference in a soap bubble. The iridescence is due to thin-film interference.
The Very Large Array, an interferometric array formed from many smaller telescopes, like many larger radio telescopes.

Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves.

Faraday holding a piece of glass of the type he used to demonstrate the effect of magnetism on polarization of light, c. 1857.

Faraday effect

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Physical magneto-optical phenomenon.

Physical magneto-optical phenomenon.

Faraday holding a piece of glass of the type he used to demonstrate the effect of magnetism on polarization of light, c. 1857.
GaAs-Faraday rotation spectrum

The Faraday effect causes a polarization rotation which is proportional to the projection of the magnetic field along the direction of the light propagation.

1936 neon marquee sign for a theater in Auburn, California, as rebuilt in 2006. The large letters on the tower are illuminated in a timed sequence that repeats, "S", "ST", "STA", "STAT", "STATE", off.

Neon sign

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In the signage industry, neon signs are electric signs lighted by long luminous gas-discharge tubes that contain rarefied neon or other gases.

In the signage industry, neon signs are electric signs lighted by long luminous gas-discharge tubes that contain rarefied neon or other gases.

1936 neon marquee sign for a theater in Auburn, California, as rebuilt in 2006. The large letters on the tower are illuminated in a timed sequence that repeats, "S", "ST", "STA", "STAT", "STATE", off.
Neon sign
An enormous number of colors can be created by combinations of different gases and fluorescent coatings in the tube.
A neon sample display case in a glass studio
Blue Neon sign in a pastry shop
Neon
Neon bowling alley sign
Promotional signage neon

The color of the light emitted by the tube may be just that coming from the gas, or the light from the phosphor layer.

A 230-volt incandescent light bulb with a medium-sized E27 (Edison 27 mm) male screw base. The filament is visible as the mostly horizontal line between the vertical supply wires.

Incandescent light bulb

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Electric light with a wire filament heated until it glows.

Electric light with a wire filament heated until it glows.

A 230-volt incandescent light bulb with a medium-sized E27 (Edison 27 mm) male screw base. The filament is visible as the mostly horizontal line between the vertical supply wires.
A scanning electron microscope image of the tungsten filament of an incandescent light bulb
Elaborate light in Denver, Colorado
Original carbon-filament bulb from Thomas Edison's shop in Menlo Park
Alexander Lodygin on 1951 Soviet postal stamp
Carbon filament lamps, showing darkening of bulb
Sir Joseph Wilson Swan
Historical plaque at Underhill, the first house to be lit by electric lights
Comparison of Edison, Maxim, and Swan bulbs, 1885
Edison carbon filament lamps, early 1880s
Thomas Alva Edison
by Thomas Edison for an improved electric lamp, 27 January 1880
Hanaman (left) and Just (right), the inventors of the tungsten bulbs
Hungarian advertising of the Tungsram-bulb from 1906. This was the first light bulb that used a filament made from tungsten instead of carbon. The inscription reads: wire lamp with a drawn wire – indestructible.
Spectrum of an incandescent lamp at 2200 K, showing most of its emission as invisible infrared light.
Xenon halogen lamp with an E27 base, which can replace a non-halogen bulb
Thermal image of an incandescent bulb. 22–175 °C = 71–347 °F.
Spectral power distribution of a 25 W incandescent light bulb.
Destruction of a lamp filament due to air penetration
The 1902 tantalum filament light bulb was the first one to have a metal filament. This one is from 1908.
Close-up of a tungsten filament inside a halogen lamp. The two ring-shaped structures left and right are filament supports.
Incandescent light bulbs come in a range of shapes and sizes.
A package of four 60-watt light bulbs
Left to right: MR16 with GU10 base, MR16 with GU5.3 base, MR11 with GU4 or GZ4 base
40-watt light bulbs with standard E10, E14 and E27 Edison screw base
The double-contact bayonet cap on an incandescent bulb
The Centennial Light is the longest-lasting light bulb in the world.
Various lighting spectra as viewed in a diffraction grating. Upper left: fluorescent lamp, upper right: incandescent bulb, lower left: white LED, lower right: candle flame.

The useful part of the emitted energy is visible light, but most energy is given off as heat in the near-infrared wavelengths.

Treatise on Light

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Book written by Dutch polymath Christiaan Huygens that was published in French in 1690.

Book written by Dutch polymath Christiaan Huygens that was published in French in 1690.

Origin of light waves as shown in Treatise on Light
Wave refraction in the manner of Huygens

The book describes Huygens' conception of the nature of light propagation which makes it possible to explain the laws of geometrical optics shown in Descartes' Dioptrique, which Huygens aimed to replace.