When implemting the Phong Light Equation
I = (Ka * Ia) +( Kd * I * NdotL) + (Ks * I * (VdotR)^n),
the specular coefficient Ks is usually not the same as the diffuse
coefficient Kd. The assumption is often made that specular highlights
are determined by the color of the light source, not the material, e.g.
for white light, Ksr=Ksg=Ksb=1.0 (this is true of plastic).
By making this assumption, however, lowering the sharpness value (n) to
mimic a dull surface such as cardboard has the effect of broadening the
range of specular visibility (which is good) but the specular highlight
is too bright (with white light).
The fact is, specular highlights are determined by both the light and
the material. Thus what appears to be needed is an array of specular
coefficients, which vary with the light intensity, for various surfaces.
Do such arrays exists anywhere?