Open main menu  Search  Wiki Loves Monuments: Photograph a monument, help Wikipedia and win!Learn more Light Language Download PDF Watch Edit "Visible light" redirects here. For light that cannot be seen with human eye, see Electromagnetic radiation. For other uses, see Light (disambiguation) and Visible light (disambiguation). Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be perceived by the human eye.[1] Visible light is usually defined as having wavelengths in the range of 400–700 nanometers (nm), or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).[2][3] This wavelength means a frequency range of roughly 430–750 terahertz (THz).  A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.  Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli Fantina, Sicily 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. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight. Some species of animals generate their own light, a process called bioluminescence. For example, fireflies use light to locate mates, and vampire squids use it to hide themselves from prey. 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 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 a vacuum.[4] In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.[5][6] In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Like all types of EM radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed. The absorbed energy of the EM waves is called a photon, and represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave instantly collapses to a single location, and this location is where the photon "arrives." This is what is called the wave function collapse. This dual wave-like and particle-like nature of light is known as the wave–particle duality. The study of light, known as optics, is an important research area in modern physics. Electromagnetic spectrum and visible light Speed of light Optics Light sources Units and measures Light pressure Historical theories about light, in chronological order See also Notes References External links Last edited 1 month ago by RHodnett RELATED ARTICLES Electromagnetic radiation Form of energy emitted and absorbed by particles which are charged which shows wave-like behavior as it travels through space Electromagnetic spectrum Entire range of frequencies of electromagnetic radiation Non-ionizing radiation electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules  Content is available under CC BY-SA 3.0 unless otherwise noted. Privacy policy Terms of Use Desktop
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