Alain schrieb:
> The front plus back values sum should be less or equal than one. Also, 
> as before, the total diffuse plus the ambient should add to one or less.
> BUT, there is nothing preventing you from having diffuse 1,1 if you want 
> to.
> 
> The specular/phong hilights can give a total larger than one when 
> combined with the oter parameters.

I /think/ you're wrong, theoretically:

- Light reflected in a rather directed fashion is unavailable for 
diffuse reflection, and therefore the diffuse term(s) [1] should be 
reduced accordingly when using specular or phong highlights.

- Ambient, on the other hand, is used not to model what happens with 
incoming light, but how much incoming light there is in the first place, 
by specifying an "input" term to add to whatever comes from regular 
light sources. The idea is to model light scattered diffusely from other 
objects onto this one, and should therefore be proportional(!) to 
other(!) nearby objects' diffuse term. (Unless ambient is used to model 
glowing objects of course.)

[1] As for backside vs. frontside diffuse term, it should be noted that 
light making it though to the other side of the object is unavailable 
for diffuse reflection on this side.

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