Light

visible lightvisiblelight sourcewave theory of lightopticallight wavelight waveselectromagnetic theory of lightlight reflectionvisible-light
dispersing a beam of white light.wikipedia
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Dispersion (optics)

dispersiondispersivechromatic dispersion
dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.
Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, in gravity waves (ocean waves), and for telecommunication signals along transmission lines (such as coaxial cable) or optical fiber.

Human eye

eyeeyeseyeball
The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight.
The human eye is an organ which reacts to light and pressure.

Electromagnetic radiation

electromagnetic waveelectromagnetic waveselectromagnetic
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

Infrared

IRnear-infraredinfra-red
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10 −7 to 7.00 × 10 −7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).
Infrared radiation (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye, although IR at wavelengths up to 1050 nanometers (nm)s from specially pulsed lasers can be seen by humans under certain conditions.

Ultraviolet

ultraviolet lightUVultraviolet radiation
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10 −7 to 7.00 × 10 −7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).
Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays.

Electromagnetic spectrum

spectrumspectrawhite light
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
This frequency range is divided into separate bands, and the electromagnetic waves within each frequency band are called by different names; beginning at the low frequency (long wavelength) end of the spectrum these are: radio waves, microwaves, terahertz waves, infrared, visible light, ultraviolet, X-rays, and gamma rays at the high-frequency (short wavelength) end.

Visible spectrum

visiblevisible lightspectrum
The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight.
Electromagnetic radiation in this range of wavelengths is called visible light or simply light.

Sunlight

sunshinesolar radiationnatural light
Sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them.
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light.

Photosynthesis

photosyntheticphotosynthesizephotosynthesizing
This process of photosynthesis provides virtually all the energy used by living things.
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities.

Fire

firesflamefire damage
Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps.
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.

Electric light

light bulblightbulbelectric lighting
With the development of electric lights and power systems, electric lighting has effectively replaced firelight.
An electric light is a device that produces visible light from electric current.

Bioluminescence

bioluminescentluminescentlight-producing
Some species of animals generate their own light, a process called bioluminescence.
Bioluminescence is the production and emission of light by a living organism.

Wavelength

wavelengthsperiodsubwavelength
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10 −7 to 7.00 × 10 −7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).
Examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor.

Frequency

frequenciesperiodperiodic
This wavelength means a frequency range of roughly 430–750 terahertz (THz).
Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.

Spectrum

spectraspectralenergy spectrum
The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature.
The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism.

Speed of light

clight speedvelocity of light
The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature.
Though this speed is most commonly associated with light, it is in fact the speed at which all massless particles and changes of the associated fields travel in vacuum (including electromagnetic radiation and gravitational waves).

Optics

opticalopticoptical device
The study of light, known as optics, is an important research area in modern physics.
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. Optics usually describes the behaviour of visible, ultraviolet, and infrared light.

Photon

photonslight quantalight
EMR in the visible light region consists of quanta (called photons) that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule.
The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force (even when static via virtual particles).

Photomorphogenesis

photomorphogeniclight
Plant growth is also affected by the color spectrum of light, a process known as photomorphogenesis.
In developmental biology, photomorphogenesis is light-mediated development, where plant growth patterns respond to the light spectrum.

Intensity (physics)

intensityintensitieslight intensity
The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature.
It is used most frequently with waves (e.g. sound or light), in which case the average power transfer over one period of the wave is used.

Microwave

microwavesmicrowave radiationmicrowave tube
In this sense, gamma rays, X-rays, microwaves and radio waves are also light.

Rod cell

rodsrodrod cells
Above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the very short (below 360 nm) ultraviolet wavelengths and are in fact damaged by ultraviolet.
Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells.

Visual perception

visionsighteyesight
The word usually refers to visible light, which is the visible spectrum that is visible to the human eye and is responsible for the sense of sight.
The human visual system is generally believed to perceive visible light in the range of wavelengths between 370 and 730 nanometers (0.00000037 to 0.00000073 meters) of the electromagnetic spectrum.

Cone cell

conesconecone cells
Above the range of visible light, ultraviolet light becomes invisible to humans, mostly because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the very short (below 360 nm) ultraviolet wavelengths and are in fact damaged by ultraviolet.
They are responsible for color vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light.

Optical phenomena

optical phenomenonatmospheric phenomenaatmospheric phenomenon
The observation and study of optical phenomena such as rainbows and the aurora borealis offer many clues as to the nature of light.
Optical phenomena are any observable events that result from the interaction of light and matter.