Christopher James Huff <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> Your < 7.5, 5, 1> light source only *looks* white when shining on a
> surface where the reflected color is >= < 1, 1, 1>. Internally, it is
> really < 7.5, 5, 1>, and avery dark surface, thick media, or other
> circumstances can give visible effects from these high light
> intensities.

Ah, so reflection (and probably specular or phong) will still see it
correctly as long it's <1. That's probably what I'm seeing.
>
> So with a fade_distance of 1 and fade_power 2, the light intensity from
> your < 7.5, 5, 1> light source at a distance of 5 units will be:
> < 0.576923077, 0.384615385, 0.0769230769>

It's distances less than fade_distance I'm most interested in.

> A fade_power of 2 is most realistic (approximating the inverse-square
> law), 10 doesn't correspond to any real-world effect.

That's the beauty of being utterly ignorant of real world mathmatics... I
can just do weird stuff without worrying about whether it's realistic or not
;-)

And fade_distance
> is just used to control the falloff rate, it has nothing to do with the
> camera position.

Oops, actually, I meant the distance between light_source & object, not
light_source & camera...

The
> distance given to fade_distance is the distance where the light is at
> the specified brightness, it decreases with distance from there, and
> increases as the distance drops below fade_distance. (the documentation
> appears to be slightly incorrect about this: only the ratio of
> distance/fade_distance matters, not the size of fade_distance in
> relation to 1)

Ok, that was confusing me too.

The main reason I use high fade_power is to simulate sunlight which is
waaaay bright, but seldom pure white. So I set the color I want the light to
be then boost fade_power way up.

An example is my Old Technology IRTC entry
(http://www.irtc.org/ftp/pub/stills/2003-02-28/async_rg.jpg) where I'm using
fade_power 7, fade_distance 1000 so everything in the scene is within the
fade_distance.  But I'm using scattering media atmosphere, and as you say
above, that can still use the higher intensity.  And looking at it now, the
color is most noticable where there is reflection or specular highlights.
And it does say in the docs that reflected or refracted light is not
attenuated, so I guess that explains it.

Thanks for the explanation.  So, ok, it doesn't work the way I thought it
did, but as long as it works...

RG

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