Hi,

> As I understand it, POV's area lights pretty much are crude hacks. Their
> *only* purpose is to create soft shadows, not to accurately simulate
> flat-panel lighting or arrays of point lights.. and because they only
> calculate shadows, they can do so much faster than a real light array
> while using less memory. Even today this is valuable; in the past it
> would have been necessary.

As I've been coming to understand over the last 24 hours, the point of
area_lights in Povray, and seeming the reason they were included as they
are, is simply to cast soft-edged shadows. And it's obvious as to why we'd
want soft edged shadows available as a feature - they are all around us in
the real world, there are very few lightsources that I can think of that
could even remotely be considered point light sources.

However, I think they way that Povray goes about creating soft-edged shadows
is *all wrong*. It would appear that the area_lights were written purely for
the shadows, and let the illumination be damned. However, I find this
incredibly counterintuitive. Shadows only exist because of an absence of
light; shadows are only a secondary effect, not the primary one. In my
opinion, it is the special type of *illumination* that should set
area_lights apart from other lights in Povray, with the fact that they cast
illumination from their entire surface area (Povray's implementation of
area_lights doesn't bother with this - they only affect the diffuse and
other aspects of the scene as if they were a point source). The soft edged
shadows should only be a naturally occuring secondary consequence of the
settings that the user applies to the size of the area_light lightsource.
Povray at the moment works mostly like the reverse of this - the user sets
up settings to get the shadows to look and behave a certain way, and the
illumination is only a secondary concern. That is what I think makes
Povray's area_lights a cheap hack.

> In regards to Christoph's "theoretical" comment, I suspect he means to
> say that having over a hundred point lights for every light in a scene
> may be practical for simple test scenes, but would make rendering for
> many real scenes unacceptably slow. I have often found the same to be
> true of high radiosity settings.

Have a look at my reply to Jaime Vives Piqueres above - I describe (in too
much detail to repost here) a very intensive test scene I did with my point
light array macro, with fairly high radiosity settings, very high quality
antialiasing on an average machine that I was using during the day, and the
scene finished fairly quickly, much quicker then I would have expected,
considering what Warp said on his webpage about how slow the "array of point
lights" method was.

> I do find the "stadium lighting" effect on the half-marble strange,
> though. Are you sure you're using the area light properly?

Again, have a look at my reply to Ben Birdsey near the top of the thread, I
posted the settings used for the arealight in that test. Also, the source
code download for my article should be fixed now if you want to download the
whole scene yourself.


John

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