Light

Visible light (commonly referred to simply as light) is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has a wavelength in the range of about 380 nanometres to about 740 nm – between the invisible infrared, with longer wavelengths and the invisible ultraviolet, with shorter wavelengths.

Primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, and polarisation, while its speed in a vacuum, 299,792,458 meters per second (about 300,000 kilometers 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.

In common with all types of EMR, 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. The study of light, known as optics, is an important research area in modern physics.

In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. This article focuses on visible light. See the electromagnetic radiation article for the general term.

Read more about Light:  Speed of Visible Light, Electromagnetic Spectrum and Visible Light, Optics, Light Sources, Units and Measures, Light Pressure

Famous quotes containing the word light:

    ... by desiring what is perfectly good, even when we don’t quite know what it is and cannot do what we would, we are part of the divine power against evil—widening the skirts of light and making the struggle with darkness narrower.
    George Eliot [Mary Ann (or Marian)

    The skylines lit up at dead of night, the air- conditioning systems cooling empty hotels in the desert and artificial light in the middle of the day all have something both demented and admirable about them. The mindless luxury of a rich civilization, and yet of a civilization perhaps as scared to see the lights go out as was the hunter in his primitive night.
    Jean Baudrillard (b. 1929)

    What is lawful is not binding only on some and not binding on others. Lawfulness extends everywhere, through the wide-ruling air and the boundless light of the sky.
    Empedocles 484–424 B.C., Greek philosopher. The Presocratics, p. 142, ed. Philip Wheelwright, The Bobbs-Merrill Co., Inc. (1960)