3D Graphics Programming with QuickDraw 3D 1.5.4

Directional Lights

A directional light is a light source that emits parallel rays of light in a specific direction. You can think of a directional light as a light source that is infinitely far away from the surfaces it is illuminating. For example, for scenes on the surface of the Earth, the sun is effectively a directional light.

Directional lights are therefore sometimes also called infinite lights.

A directional light has no location. As a result, you specify the direction of the light as a vector equivalent to the direction of the light. In addition, a directional light cannot suffer attenuation (that is, a loss of intensity over distance). It can, however, cast shadows.