light (disambiguation). Page semi-protected The Sun is Earths primary source of light. About 44% of the suns electromagnetic radiation that reaches the ground is in the visible light range. Light usually refers to visible light, which is electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as having a wavelength in the range of 400 nanometres (nm), or 400×10−9 m, to 700 nanometres – between the infrared, with longer wavelengths and the ultraviolet, with shorter wavelengths.[2][3] The main source of light on earth is the sun. Sunlight provides the energy that green plants use to create sugars, 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 invention of electricity, electric lighting has all but replaced firelight. 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.
Posted on: Fri, 12 Dec 2014 10:43:54 +0000
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