What is light,luminous flux, illumination?

Light is a form of energy, which is radiated by heated bodies. The light is the part of the radiant energy which produces a sensation (of light) in the human eye.

Luminous flux is the light energy radiated per second from a luminous body in the form of light waves. It is measured in lumen.

The luminous flux falling per unit area on a surface is known as illumination and is expressed in Lumen/m2.