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

Quantum

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Minimum amount of any physical entity (physical property) involved in an interaction.

Minimum amount of any physical entity (physical property) involved in an interaction.

For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation).

The spectrum in a rainbow

Spectrum

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Condition that is not limited to a specific set of values but can vary, without gaps, across a continuum.

Condition that is not limited to a specific set of values but can vary, without gaps, across a continuum.

The spectrum in a rainbow
Diagram illustrating the electromagnetic spectrum
Mass spectrum of Titan's ionosphere
Spectrogram of dolphin vocalizations
A Nolan chart of the political spectrum using (red leftism and blue rightism) coding

The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism.

The human eye of the right side of the face, showing a white sclera with some blood vessels, a green iris, and the black pupil

Human eye

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The human eye of the right side of the face, showing a white sclera with some blood vessels, a green iris, and the black pupil
A detailed depiction of eye using a 3D medical illustration
MRI scan of human eye
Schematic diagram of the human eye. It shows a horizontal section through the right eye.
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Side-view of the human eye, viewed approximately 90° temporal, illustrating how the iris and pupil appear rotated towards the viewer due to the optical properties of the cornea and the aqueous humour
The light circle is the optic disc where the optic nerve exits the retina
The two eyes converge to point to the same object.
Conjunctival injection, or redness of the sclera surrounding the iris and pupil
Eye and orbit anatomy with motor nerves
Image showing orbita with eye and nerves visible (periocular fat removed)
Image showing orbita with eye and periocular fat
Normal anatomy of the human eye and orbit, anterior view
Right eye without labels (horizontal section)
The structures of the eye labeled
Another view of the eye and the structures of the eye labeled

The human eye is a sensory organ, part of the sensory nervous system, that reacts to visible light and allows us to use visual information for various purposes including seeing things, keeping our balance, and maintaining circadian rhythm.

Incandescent (left) and compact fluorescent (right) light bulbs turned on

Electric light

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Incandescent (left) and compact fluorescent (right) light bulbs turned on
Elaborate light in Denver, Colorado
Electric light longevity and brightness testing in an integrating sphere
Sign with instructions on the use of light bulbs
A tablet at St John the Baptist Church, Hagley commemorates the installation of electric light in 1934.
Top, two compact fluorescent lamps. Bottom, two fluorescent tube lamps. A matchstick, left, is shown for scale.
LED lamp with E27 Edison screw base
The 15 kW xenon short-arc lamp used in the IMAX projection system.
A mercury arc lamp from a fluorescence microscope.
In this composite image from October 2012, human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States, India, Japan and South Korea.
A clear glass 60 W light bulb
The cross in a circle usually represents a lamp as an indicator. (ANSI/IEEE Std 315A-1986)
The semicircular dent in a circle, which usually represents a lamp as a source of light or illumination.

An electric light is a device that produces visible light from electric power.

Hydrogen's purple glow in its plasma state, the most abundant in the universe

Matter

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Any substance that has mass and takes up space by having volume.

Any substance that has mass and takes up space by having volume.

Hydrogen's purple glow in its plasma state, the most abundant in the universe
Under the "quarks and leptons" definition, the elementary and composite particles made of the quarks (in purple) and leptons (in green) would be matter—while the gauge bosons (in red) would not be matter. However, interaction energy inherent to composite particles (for example, gluons involved in neutrons and protons) contribute to the mass of ordinary matter.
Quark structure of a proton: 2 up quarks and 1 down quark.
A comparison between the white dwarf IK Pegasi B (center), its A-class companion IK Pegasi A (left) and the Sun (right). This white dwarf has a surface temperature of 35,500 K.
Phase diagram for a typical substance at a fixed volume. Vertical axis is Pressure, horizontal axis is Temperature. The green line marks the freezing point (above the green line is solid, below it is liquid) and the blue line the boiling point (above it is liquid and below it is gas). So, for example, at higher T, a higher P is necessary to maintain the substance in liquid phase. At the triple point the three phases; liquid, gas and solid; can coexist. Above the critical point there is no detectable difference between the phases. The dotted line shows the anomalous behavior of water: ice melts at constant temperature with increasing pressure.
Galaxy rotation curve for the Milky Way. Vertical axis is speed of rotation about the galactic center. Horizontal axis is distance from the galactic center. The sun is marked with a yellow ball. The observed curve of speed of rotation is blue. The predicted curve based upon stellar mass and gas in the Milky Way is red. The difference is due to dark matter or perhaps a modification of the law of gravity. Scatter in observations is indicated roughly by gray bars.

However it does not include massless particles such as photons, or other energy phenomena or waves such as light or heat.

The visual dorsal stream (green) and ventral stream (purple) are shown. Much of the human cerebral cortex is involved in vision.

Visual perception

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Ability to interpret the surrounding environment through photopic vision , color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflected by objects in the environment.

Ability to interpret the surrounding environment through photopic vision , color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum reflected by objects in the environment.

The visual dorsal stream (green) and ventral stream (purple) are shown. Much of the human cerebral cortex is involved in vision.
Leonardo da Vinci: The eye has a central line and everything that reaches the eye through this central line can be seen distinctly.
Eye movement first 2 seconds (Yarbus, 1967)

The human visual system is generally believed to be sensitive to visible light in the range of wavelengths between 370 and 730 nanometers (0.00000037 to 0.00000073 meters) of the electromagnetic spectrum.

Normalized responsivity spectra of human cone cells, S, M, and L types

Cone cell

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Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye.

Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye.

Normalized responsivity spectra of human cone cells, S, M, and L types
Cone cell structure
Bird, reptilian, and monotreme cone cells

They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision.

A ray of light being refracted in a plastic block.

Refraction

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Redirection of a wave as it passes from one medium to another.

Redirection of a wave as it passes from one medium to another.

A ray of light being refracted in a plastic block.
Refraction of light at the interface between two media of different refractive indices, with n2 > n1. Since the phase velocity is lower in the second medium (v2 < v1), the angle of refraction θ2 is less than the angle of incidence θ1; that is, the ray in the higher-index medium is closer to the normal.
A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.
When a wave moves into a slower medium the wavefronts get compressed. For the wavefronts to stay connected at the boundary the wave must change direction.
A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.
An image of the Golden Gate Bridge is refracted and bent by many differing three-dimensional drops of water.
The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.
Heat haze in the engine exhaust above a diesel locomotive.
Mirage over a hot road.
Water waves are almost parallel to the beach when they hit it because they gradually refract towards land as the water gets shallower.

Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction.

The fire tetrahedron

Fire

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The fire tetrahedron
A candle's flame
Northwest Crown Fire Experiment, Canada
Photo of a fire taken with a 1/4000th of a second exposure
Fire is affected by gravity. Left: Flame on Earth; Right: Flame on the ISS
Bushman starting a fire in Namibia
Process of ignition of a match
Painting of the Cathedral and the Academy building after the Great Fire of Turku, by Gustaf Wilhelm Finnberg, 1827
Hamburg after four fire-bombing raids in July 1943, which killed an estimated 50,000 people
A coal-fired power station in the People's Republic of China
Fire-damaged restaurant waiting for demolition
Disability-adjusted life year for fires per 100,000 inhabitants in 2004 
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less than 50
50–100
100–150
150–200
200–250
250–300
300–350
350–400
400–450
450–500
500–600
more than 600

Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.

Cross section of the retina. Rods are visible at far right.

Rod cell

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Cross section of the retina. Rods are visible at far right.
Anatomy of a Rod Cell
Wavelength responsiveness of short (S), medium (M) and long (L) wavelength cones compared to that of rods (R).

Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells.