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:
“Awareness of the stars and their light pervades the Koran, which reflects the brightness of the heavenly bodies in many verses. The blossoming of mathematics and astronomy was a natural consequence of this awareness. Understanding the cosmos and the movements of the stars means understanding the marvels created by Allah. There would be no persecuted Galileo in Islam, because Islam, unlike Christianity, did not force people to believe in a “fixed” heaven.”
—Fatima Mernissi, Moroccan sociologist. Islam and Democracy, ch. 9, Addison-Wesley Publishing Co. (Trans. 1992)
“As one child psychologist friend of mine explains it with tongue in cheek, your baby only needs a lot of light at night if he’s reading or he’s entertaining guests.”
—Lawrence Kutner (20th century)
“There yet remains but one concluding tale,
And then this chronicle of mine is ended—
Fulfilled, the duty God ordained to me,
A sinner. Not without purpose did the Lord
Put me to witness much for many years
And educate me in the love of books.
One day some indefatigable monk
Will find my conscientious, unsigned work;
Like me, he will light up his ikon-lamp
And, shaking from the scroll the age-old dust,
He will transcribe these tales in all their truth.”
—Alexander Pushkin (1799–1837)