The 3-Point Lighting Scale-

The Three-Point light Scale-

The Key Light- 

This is the primary light source 
It is the intense and most influential direct light source 
It is placed to one side

Is used to illuminate the subject 

The Fill Light-

This light is used to fill shadows created by the key light, it is a softer and less bright light compared to the key light.

It is placed opposite the key light

The Back Light-

This light is used to light the subject from the rear
This light separates the subject from the background 

This is placed higher than the subject it is lighting 
this provides the object with an outline 

Gels-