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    <p>I found a suitable illumination model myself in the <a href="http://local.wasp.uwa.edu.au/~pbourke/dataformats/mtl/" rel="nofollow">documentation for .mtl files</a>:</p> <pre><code>color = KaIa + Kd { SUM j=1..ls, (N*Lj)Ij } + Ks ({ SUM j=1..ls, ((H*Hj)^Ns)Ij Fr(Lj*Hj,Ks,Ns)Ij} + Fr(N*V,Ks,Ns)Ir}) + (1.0 - Kx)Ft (N*V,(1.0-Ks),Ns)TfIt </code></pre> <p>This is dense and actually has some typos (like <code>Kx</code> and <code>Ft</code>), so I corrected it:</p> <pre><code>I = Ka * Ia + Kd * [sum for each light: (N . L) * Il] + Ks * [sum for each light: ((R . V) ^ Ps) * Fl * Il] + Ks * Fr * Ir + Kt * (1 - Ks) * Ft * It I := surface point's color V := ray direction P := surface point N := surface normal L := light's position - P R := L - 2 * (N . L) * P Ka := surface material's ambient coefficient Kd := surface material's diffuse coefficient Ks := surface material's specular coefficient Ps := surface material's shininess Kt := surface material's transmission coefficient Ia := ambient light color Il := light's color Ir := reflected ray's color It := transmitted ray's color Fl := light's Fresnel coefficient Fr := reflected Fresnel coefficient Ft := transmitted Fresnel coefficient </code></pre> <p>This model makes sense to me, especially after reading <a href="http://www.cgcoach.com/articles/the-fundamentals/cg-lighting-101/" rel="nofollow">Lighting 101</a> -- Phong specular reflection is a performance-minded hack for reflecting light sources, so it's natural to use the same coefficient for specular highlights and reflected rays.</p> <p><strong>There's still one thing I don't understand.</strong> If I don't want to bother with Fresnel terms, I can set <code>Fl</code>, <code>Fr</code>, and <code>Ft</code> to 1. If I want that extra accuracy, though, how would I calculate them in terms of my already-defined variables?</p>
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    1. POHow do I combine Phong lighting with Fresnel dielectric reflection/transmission realistically?
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