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:
“Think what a mean and wretched place this world is; that half the time we have to light a lamp that we may see to live in it. This is half our life. Who would undertake the enterprise if it were all?”
—Henry David Thoreau (18171862)
“For light doth seize my brain
With frantic pain.”
—William Blake (17571827)
“The light of memory, or rather the light that memory lends to things, is the palest light of all.... I am not quite sure whether I am dreaming or remembering, whether I have lived my life or dreamed it. Just as dreams do, memory makes me profoundly aware of the unreality, the evanescence of the world, a fleeting image in the moving water.”
—Eugène Ionesco (b. 1912)