Visible light is electromagnetic radiation whose wavelength falls within the range to which the human retina responds, i.e., between about 390 nm (violet light) and 740 nm (red). White light consists of a roughly equal mixture of all visible wavelengths, which can be separated to yield the colors of the spectrum, as was first demonstrated conclusively by Newton. In the 20th century it has become apparent that light consists of energy quanta called photons that behave partly like waves and partly like particles. The velocity of light in a vacuum is 299,792 km per second
verb (past lit /lit/; past participle lit or lighted)[with object]
Old English lēoht, līht (noun and adjective), līhtan (verb), of Germanic origin; related to Dutch licht and German Licht, from an Indo-European root shared by Greek leukos 'white' and Latin lux 'light'