It all started when...

1. something that makes things visible or affords illumination:

All colors depend on light.

2. Physics.

  1. Also called luminous energy, radiant energy. electromagnetic radiation to which the organs of sight react, ranging in wavelength from about 400 to 700 nm and propagated at a speed of 186,282 mi./sec (299,972 km/sec), considered variously as a wave, corpuscular, or quantum phenomenon.
  2. a similar form of radiant energy that does not affect the retina, as ultraviolet or infrared rays.


the sensation produced by stimulation of the organs of sight