> The last two sentences are what interest me. They seem to imply that an
> object illuminated by a point light will be exactly the same as one
> illuminated by a very large area light. Is this entirely correct? Assume
> that the scene has just the light and the object, so soft shadows can be
> ignored, unless the object is self-shadowing. I believe a sphere is not
> self-shadowing, so let's say the object is a sphere.


Correct. A sphere with nothing else in the scene will be illuminated exactly
the same with an area light as without one.

Actually, now that I think about it, the area around the shadow line might
be *slightly* different. (The shadow line might be more blurred.) But aside
from shadow calculation, the area light behaves the same. This means that
you shouldn't use area lights when they are so big that their size will
significantly affect the scene in terms of specular reflection or the
direction to them from a point on an object.

> So the only way to approximate a true area light source with soft shadows,
> is to use an array of area lights -- like the cornell example. Am I right?

An area_light approximates a true area light with soft shadows. They suffice
in most situations (rarely are area lights so large that you need to worry
about the case I mentioned above). An array of area lights could help in
such a case, I suppose... but using an array of lights rather than a single
area light covering the same area won't have any affect on the softness of
shadows.

 - Slime
[ http://www.slimeland.com/ ]

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