Structured surface bidirectional reflectance distribution function reciprocity: theory and counterexamples

I address the question of whether the bidirectional reflectance distribution function (BRDF) of a structured surface has the same value when the incident and reflected angles are reversed. In particular, I examine the validity of some recent counterexamples and contrary measurements. On the basis of a new definition for structured surfaces, I conclude that the BRDF should be reciprocal. I show that designed counterexamples are flawed and suggest that measurements that do not exhibit reciprocity can be attributed to uncertainty and uncontrolled factors.