What is Light?
{{redirect|Visible light|all parts of the electromagnetic spectrum that can be seen by the eye|Visible spectrum}} [[File:Light spectrum on a wall caused by sunlight going through prism and then handmade glass.jpg|thumb|Rays, or beams of light shine through metal patterns into a railway station.]]'''Light''' is a form of [[electromagnetic radiation]]. It is natural agent that stimulates [[sight]] and makes things easy to see. Light is the opposite of [[darkness]]. Light has a [[wavelength]]. Some wavelengths can be seen by the [[human]] [[eye]]. Others cannot.<ref>International Commission on Illumination 1987. [http://www.cie.co.at/publ/abst/17-4-89.html ''International Lighting Vocabulary''] {{Webarchive|url=https://web.archive.org/web/20100227034508/http://www.cie.co.at/publ/abst/17-4-89.html |date=2010-02-27 }}. Number 17.4. CIE, 4th edition. {{ISBN|978-3-900734-07-7}}.<br>By the ''International Lighting Vocabulary'', the definition of ''light'' is: “Any radiation capable of causing a visual sensation directly.”</ref> Many animals can see light. They need it to find food, water, and other things. Light makes up a part of both the [[electromagnetic spectrum]] and [[radiation]] given by [[star]]s, like the [[sun]]. The light that comes from the sun reaches the Earth and makes it bright. This is called daytime. The study of light is known as [[optics]]. When light hits an opaque object, it makes a [[shadow]]. When light hits a transparent object, it passes through it almost completely without making a significant [[shadow]]. Light is a form of electromagnetic radiation that shows properties of both [[wave]]s and [[Particle physics|particles]]. It is a form of energy. Light also keeps the Earth warm. Light exists in tiny energy packets called [[photons]]. Each wave has a [[wavelength]] or [[frequency]]. The human eye sees each wavelength as a different [[color]]. [[Rainbow]]s show the entire [[spectrum]] of visible light. The separate colors, moving in from the outer edges, are [[red]], [[Orange (color)|oran