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: the form of energy that makes it possible to see things : the brightness produced by the sun, by fire, a lamp, etc.
: a source of light (such as an electric lamp)
: a light on a vehicle
Full Definition of LIGHT
a: something that makes vision possible
b: the sensation aroused by stimulation of the visual receptors
c: electromagnetic radiation of any wavelength that travels in a vacuum with a speed of about 186,281 miles (300,000 kilometers) per second; specifically: such radiation that is visible to the human eye
: to fall unexpectedly —usually used with on or upon
: to arrive by chance :happen —usually used with on or upon<lit upon a solution>
— light into
: to attack forcefully <I lit into that food until I'd finished off the heel of the loaf — Helen Eustis>
Origin of LIGHT
Middle English, from Old English līhtan; akin to Old English lēoht light in weight
First Known Use: before 12th century
That portion of the electromagnetic spectrum visible to the human eye. It ranges from the red end to the violet end of the spectrum, with wavelengths from 700 to 400 nanometres and frequencies from 4.3 1014 to 7.5 1014 Hz. Like all electromagnetic radiation, it travels through empty space at a speed of about 186,000 mi/sec (300,000 km/sec). In the mid-19th century, light was described by James Clerk Maxwell in terms of electromagnetic waves, but 20th-century physicists showed that it exhibits properties of particles as well; its carrier particle is the photon. Light is the basis for the sense of sight and for the perception of colour. See alsooptics; wave-particle duality.