-Stores properties of a single light source. Lights can be directional, point
-lights or spotlights. No explicit type parameter is provided; rather the
-other parameters determine what kind of light it is. If the fourth component
-of position is zero, it's a directional light. Otherwise, if the spot cutoff
-is not 180 degrees, it's a spotlight. Otherwise it's an omnidirectional point
-light.
+Base class for light sources. The DirectionalLight and PointLight classes
+implement different types of lights.