Difference between revisions of "Light"
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Revision as of 10:22, 10 April 2016
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum.
Contents
Description
The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.
Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or Template:Val to Template:Val, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).
This wavelength means a frequency range of roughly 430–750 terahertz (THz). Often, infrared and ultraviolet are also called light.
Sunlight and photosynthesis
The main source of light on Earth is the Sun.
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.
This process of photosynthesis provides virtually all the energy used by living things.
Fire
Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps.
Electric lighting
With the development of electric lights and of power systems, electric lighting has all but replaced firelight.
Bioluminescence
Some species of animals generate their own light, called bioluminescence.
For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey.
Properties
Primary properties of visible light:
- Intensity
- Propagation direction
- Frequency or wavelength spectrum
- Polarization
- Speed
Speed of light
The speed of light in a vacuum, 299,792,458 meters per second, is one of the fundamental constants of nature.
Visible light, as with all types of electromagnetic radiation (EMR), is experimentally found to always move at this speed in vacuum.
Electromagnetic radiation of any wavelength
In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.
In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of light, visible light is emitted and absorbed in tiny "packets" called photons, and exhibits properties of both waves and particles. This property is referred to as the wave–particle duality.
Optics
The study of light, known as optics, is an important research area in modern physics.
James Turrell, Roden Crater
James Turrell is an American artist primarily concerned with light and space.
Turrell is best known for his work in progress, Roden Crater, a natural cinder cone crater located outside Flagstaff, Arizona that he is turning into a massive naked-eye observatory.
Darkness
Darkness, the polar opposite to brightness, is understood to be an absence of visible light.
See also
- Animation
- Centre for International Light Art
- Color
- Color fastness
- Darkness
- Dreamachine
- Eigengrau
- Electromagnetic radiation
- Electromagnetic spectrum
- Film
- Fire
- Ganzfeld effect
- Gegenschein
- Infrared Data Association
- James Turrell
- Light art
- Lightfastness
- Miksang
- Mind machine
- Naked-eye observatory
- Optics
- Photography
- Photon
- Phi phenomenon
- Physics
- Prisoner's cinema
- Roden Crater
- Scrying
- Spectrum
- Stroboscopic light
- Visible light
- Zodiacal light
External links
- Light @ Wikipedia
