Half Life 2 used a "Half Lambert" diffuse term
Yup, another excellent formula. I saw this half life formula described as "the dot product from the Lambertian model is scaled by ½, add ½ and squared"
I interpreted this as the following -> ((NdotL1 * 0.5) + 0.5) * ((NdotL1 * 0.5) + 0.5)
The model looks very similar as with the above RenderMan equation but this one better retains the illusion of depth. Thanks for the tip.