The Point Light Painters will act similar to default UE4 Point Lights and cast their light in all Directions.
The Cube Light Painters will fill a Cube Volume with Light. This can be useful for Rooms where normal Point Lights could not fill "just" the Room Area and let the Light bleed outside of the Room.
The Square Light Painter is a directional Light. It can be shaped as a Square, a Circle or something inbetween. It can be compared to the default UE4 Spot Light, but with the Difference that it can only shine its Light into 1 Direction.