Lewis, Robert R.2014-10-212014-10-2119941467-8659https://doi.org/10.1111/1467-8659.1320109There is a need to develop shaders that not only"look good", but are more physically plausible. From physical and geometric considerations, we review the derivation of a shading equation expressing rejected radiance in terms of incident radiance and the bidirectional reflectance distribution function (BRDF). We then examine the connection between this equation and conventional shaders used in computer graphics. Imposing the additional physical constraints of energy conservation and Helmholtz reciprocity allows us to create variations of the conventional shaders that are more physically plausible.10.1111/1467-8659.1320109109-120