Am 06.08.2018 um 07:57 schrieb Mike Horvath:
> In one of my scenes, I have constructed my own area light by placing
> multiple point lights using spherical coordinates, so that a bulb or sun
> is simulated and shadows are smoothed a bit.
...
> However, IIRC, POV-Ray's own area light syntax allows for similar
> effects. What are the advantages of POV-Ray area lights over the method
> I selected above?

Firs of all, from a quick glance at your code it seems to me that you're
actually constructing a (uniform) light dome, not an area light. At
present, POV-Ray doesn't do light domes (except indirectly via sky
spheres and radiosity).

The difference between a light dome and an area light is that a light
dome covers an entire hemisphere (or even an entire sphere), while an
area light is (or simulates) a localized array of light sources.

Now if we're talking about area lights, the advantages of genuine area
lights over a homebrew array of light sources is as follows:

- Easier to set up.

- Lower memory footprint (which may also improve render speed due to
better CPU cache utilization).

- [optional] Adaptive sampling of the shadow rays, tracing as few as 4
rays per area light if it is unobstructed or completely obstructed, but
as many rays as you like if it is partially obstructed (in a process
similar to adaptive anti-aliasning), for faster rendering at high quality.

- [optional] Jittering of the "lightlets" to break up pattern-like
artifacts caused by the regular arrangement of the lightlets, trading
them for less obvious noise-like artifacts.

- [optional] Substituting a single light source for the entire area
light in certain computations, most notably diffuse and specular
shading, for faster rendering at low cost in quality.

- [optional] Dynamic re-orientation of the area light to simulate a
spherical (as opposed to flat disc-like or rectangular) light source
without having to add more lights for same quality.

- Possibly one or two other optimizations that I may currently be
forgetting about.

There are, of course, also drawbacks:

- Less flexibility in the arrangement of "lightlets" (you're stuck with
lines, rectangles, discs, and quasi-spheres).

- Non-ideal "lightlet" pattern in the spherical case, potentially
leading to (usually subtle) directional artifacts.


As mentioned above, POV-Ray does not provide an area-light-like
mechanism for light domes. What you /can/ do however is create a light
dome out of area lights, probably allowing you to get away with fewer
light sources.

Post a reply to this message