scott <sco### [at] scottcom> wrote:
> This is what happens IRL though, isn't it? An sRGB red light source will
> have a very narrow spectrum and almost no overlap at all with the
> reflective spectrum of an sRGB blue surface, so it will appear black.
>
> I always avoid zero terms in rgb colours too, not because I'm trying to
> fake anything but I think it is genuinely more realistic for natural
> surfaces and lights.

Mostly, a colored light means a tinted glass, which has a broad spectrum (except
for LED). And even if you do have such a light, the material you are
illuminating will certainly not have a narrow reflective spetrum. If you
illuminate with a red light, you will usually be able to get some red component
from a blue material, especially since there is no blue reflected light to
overshadow it. I'm not saying the effect is strong, but it is enough to create
more natural lighting. You can approximate this by just having nonzero
components, but spectral response gives you more flexibility.

It's also easier to get a realistic illumination with different color
temperature light sources. For instance, a dim tungsten light looks quite
orange, but if you just use rgb, you don't notice, that the far-spectrum blue
light is extremely dim - most of the "blue" component comes from more central
wavelengths. This will affect appearance of blue surfaces.

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