What is Light and Shadow?

Light refers to electromagnetic radiation that can be detected by the human eye. The entire electromagnetic spectrum is

extremely broad and it ranges from low energy radio waves of the wavelength range from 10−3 to 10−1 meters to high energy

gamma rays with wavelengths that range from 10−11 to 10−15

In this range, visible light falls under the wavelength of 4.00 × 10−7 to 7.00 × 10−7, meters. The range of visible light varies from 400nm for violet light to 700nm for the red light. Radiation lower than 400nm is referred to as Ultra-Violet and radiation longer than 700nm is referred to as Infra-Red, neither of which can be detected by the human eye.

Shaow:

 A shadow is an absence of light. When the light is blocked by an opaque object, it produces a dark or shaded area behind it.

For example, raise your palm in front of a torch or any light source, then you will see the shadow of your palm behind your palm.