Directional lights light all of the scene from the same direction. This is useful for simulating light from a distant object such as the sun.
Directional lights are created using the command
object new_directional_light(double red, double green, double blue, double x, double y, double z);
The x, y and z variables give the direction the light is coming from. For example, the command for a white, overhead light:
the_light = new_directional_light(1.0, 1.0, 1.0, 0, 0, 1);