Lights can be infinite (a.k.a. directional) or local
All rays from an infinite light source come in the same direction.
Rays from a local light source come from a particular point in space.
The 4th value in the light source's position controls this feature:
0 = infinite light
1 = local light
# Light comes from above
glLightfv(GL_LIGHT0, GL_POSITION, [0, 1, 0, 0])
# Light comes from point (0,1,0)
glLightfv(GL_LIGHT1, GL_POSITION, [0, 1, 0, 1])