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.
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Famous quotes containing the word light:
“Experience was to be taken as showing that one might get a five-pound note as one got a light for a cigarette; but one had to check the friendly impulse to ask for it in the same way.”
—Henry James (18431916)
“Lift your eyes
Where the roads dip and where the roads rise
Seek only there
Where the grey light meets the green air
The hermits chapel, the pilgrims prayer.”
—T.S. (Thomas Stearns)
“Loosened from the minors tether;
Free to mortgage or to sell,
Wild as wind, and light as feather
Bid the slaves of thrift farewell.”
—Samuel Johnson (17091784)