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

Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by an aluminum plate. Gamma radiation (γ) is dampened when it penetrates lead. Note caveats in the text about this simplified diagram.

Radiation

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Often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.

Often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.

Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by an aluminum plate. Gamma radiation (γ) is dampened when it penetrates lead. Note caveats in the text about this simplified diagram.
The international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for unshielded humans. Radiation, in general, exists throughout nature, such as in light and sound.
Some kinds of ionizing radiation can be detected in a cloud chamber.
Graphic showing relationships between radioactivity and detected ionizing radiation
Gamma radiation detected in an isopropanol cloud chamber.
Alpha particle detected in an isopropanol cloud chamber
Electrons (beta radiation) detected in an isopropanol cloud chamber
The electromagnetic spectrum
In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Electromagnetic radiation includes the far field part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, is part of the changing electromagnetic field, but does not count as electromagnetic radiation.

electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)

Absorption lines for air, under indirect illumination, with the direct light source not visible, so that the gas is not directly between source and detector. Here, Fraunhofer lines in sunlight and Rayleigh scattering of this sunlight is the "source." This is the spectrum of a blue sky somewhat close to the horizon, pointing east at around 3 or 4 pm (i.e., Sun toward the west) on a clear day.

Spectral line

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Absorption lines for air, under indirect illumination, with the direct light source not visible, so that the gas is not directly between source and detector. Here, Fraunhofer lines in sunlight and Rayleigh scattering of this sunlight is the "source." This is the spectrum of a blue sky somewhat close to the horizon, pointing east at around 3 or 4 pm (i.e., Sun toward the west) on a clear day.
Continuous spectrum of an incandescent lamp (mid) and discrete spectrum lines of a fluorescent lamp (bottom)

A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies.

A 22° halo around the Moon in Atherton, California

Optical phenomena

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A 22° halo around the Moon in Atherton, California
A solar halo as seen from 41° south latitude
A circumzenithal arc over Grand Forks, North Dakota
The Belt of Venus over Paranal Observatory atop Cerro Paranal in the Atacama Desert, northern Chile
Green flash appears above the solar disc for a second or so. One such occurrence was taken from Cerro Paranal.

Optical phenomena are any observable events that result from the interaction of light and matter.

Optical microscope used at the Wiki Science Competition 2017 in Thailand

Microscope

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Laboratory instrument used to examine objects that are too small to be seen by the naked eye.

Laboratory instrument used to examine objects that are too small to be seen by the naked eye.

Optical microscope used at the Wiki Science Competition 2017 in Thailand
18th-century microscopes from the Musée des Arts et Métiers, Paris
Carl Zeiss binocular compound microscope, 1914
Electron microscope constructed by Ernst Ruska in 1933
Fluorescence microscope with the filter cube turret above the objective lenses, coupled with a camera.
Types of microscopes illustrated by the principles of their beam paths
Evolution of spatial resolution achieved with optical, transmission (TEM) and aberration-corrected electron microscopes (ACTEM).
Unstained cells viewed by typical brightfield (left) compared to phase-contrast microscopy (right).
Modern transmission electron microscope
Transmission electron micrograph of a dividing cell undergoing cytokinesis
Leaf surface viewed by a scanning electron microscope.
First atomic force microscope

One way is to describe the method an instrument uses to interact with a sample and produce images, either by sending a beam of light or electrons through a sample in its optical path, by detecting photon emissions from a sample, or by scanning across and a short distance from the surface of a sample using a probe.

A dicot seedling emerging from the ground displays an apical hook (in the hypocotyl in this case), a response to dark conditions

Photomorphogenesis

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A dicot seedling emerging from the ground displays an apical hook (in the hypocotyl in this case), a response to dark conditions

In developmental biology, photomorphogenesis is light-mediated development, where plant growth patterns respond to the light spectrum.

Emission spectrum of a metal halide lamp.

Emission spectrum

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Spectrum of frequencies of electromagnetic radiation emitted due to an electron making a transition from a high energy state to a lower energy state.

Spectrum of frequencies of electromagnetic radiation emitted due to an electron making a transition from a high energy state to a lower energy state.

Emission spectrum of a metal halide lamp.
A demonstration of the 589 nm D2 (left) and 590 nm D1 (right) emission sodium D lines using a wick with salt water in a flame
Emission spectrum of hydrogen
Emission spectrum of iron
Schematic diagram of spontaneous emission

In physics, emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light.

Top to bottom: Lights flashing at frequencies, 1 Hz and 2 Hz; that is, at 0.5, 1.0 and 2.0 flashes per second, respectively. The time between each flash – the period T – is given by 1⁄f (the reciprocal of f); that is, 2, 1 and 0.5 seconds, respectively.

Hertz

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Unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Top to bottom: Lights flashing at frequencies, 1 Hz and 2 Hz; that is, at 0.5, 1.0 and 2.0 flashes per second, respectively. The time between each flash – the period T – is given by 1⁄f (the reciprocal of f); that is, 2, 1 and 0.5 seconds, respectively.
A sine wave with varying frequency
A heartbeat is an example of a non-sinusoidal periodic phenomenon that may be analyzed in terms of frequency. Two cycles are illustrated.

Light is electromagnetic radiation that is even higher in frequency, and has frequencies in the range of tens (infrared) to thousands (ultraviolet) of terahertz.

Intensity (physics)

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Power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy.

Power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy.

Intensity is used most frequently with waves such as acoustic waves (sound) or electromagnetic waves such as light or radio waves, in which case the average power transfer over one period of the wave is used.

A chemoluminescent reaction in an Erlenmeyer flask

Chemiluminescence

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Luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:

Luminol and [B] is hydrogen peroxide in the presence of a suitable catalyst we have:

A chemoluminescent reaction in an Erlenmeyer flask
Bioluminescence in nature: A male firefly mating with a female of the species Lampyris noctiluca.
Chemiluminescence after a reaction of hydrogen peroxide and luminol
Green and blue glow sticks

[A] + [B] → [◊] → [Products] + light

Illuminated cherry blossoms, light from the shop windows, and Japanese lantern at night in Ise, Mie, Japan

Lighting

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Illuminated cherry blossoms, light from the shop windows, and Japanese lantern at night in Ise, Mie, Japan
Daylight used at the train station Gare de l'Est Paris
Low-intensity lighting and haze in a concert hall allows laser effects to be visible
Dim night lighting for the old warehouses along the river in the old town of Porvoo, Finland
A demonstration of the effects of different kinds of lighting
Wall-mounted light with shadows
Animated fountain in Moscow's Square of Europe, lit at night
High mast lighting along Highway 401 in Ontario, Canada
Floodlights are used to illuminate outdoor playing fields or work zones during nighttime.
The decks and gangway of tugboat Samuel de Champlain illuminated at night while docked at a shipyard for the purposes of safety and security.
Lighting without windows: The Pantheon in the 18th century, painted by Giovanni Paolo Panini.
Lighting and shadows
Moving heads in a photo studio set
Illuminating a subject from beneath can create a heightened dramatic effect.
The Leppävaaran Torni building in Leppävaara, Espoo, Finland, illuminated with colourful lights in 2017

Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects.