Area Lights

A point light is a zero-dimensional entity: it has no size. All photons emitted by such a light source originate in the same point. When determining which photons reach some location \(P\), either all photons from a point light reach \(P\), or none of them do. This has as consequence that shadows are very sharp.

Area lights are mathematically an infinite set of point lights arranged in a rectangular area. This leads to soft shadows:

Below you can compare hard and soft shadows.