When light hits an object in its path, a combination of three things will happen:

The light will be:

Reflected

Refracted

Absorbed

Light can be produced in a variety of ways. The light source most common in stage lighting is and incandescent light bulb.

Incandescence is the point at which a heated object gives off light. The filament in the photo above is heated to the point where it begins to glow and give off light.

The Light Bulb