This is from the documentation of ?plot3d,light:
light=[phi, theta, r, g, b]
This option adds [my emphasis] a directed light source
from the direction phi, theta in spherical coordinates.
The "adds" in that sentence seems to imply that
multiple light sources are possible, but it does not seem
to work that way. Each subsequent light option overrides
the previous one as we see in the following illustration
where we render a ball three times by illuminating it
(a) from the north, (b) from the south, and (c) from
both the north and south. In (c) Maple accounts for only
the south light.
ball := sphere(1, style=surface, color=gold):