Attenuation
For real-world lights, the intensity of light decreases as distance from the light
increases, a phenomenon known as attenuation. Since a directional light is
infinitely far away, it doesn't make sense to attenuate its intensity over distance,
so attenuation is disabled for a directional light. However, you might want to
attenuate the light from a positional (point or spot) light. To do this, you can
define an attenuation factor to your light. (OpenGL has three different