Attached Link: http://www.runtimedna.com/messages.ez?forum_id=28&Form.ShowMessage=86904

BDRF, short for bi-directional reflectance distribution function, describes how a surface responds to incoming light. It's what gives a surface a look beyond just plain color - e.g. how paper looks different than plastic or flour, even when all three of them are white. Radiosity is fixed to a lambertian BRDF, which is a very simplified model and not necessarily the appropriate one for your surfaces. See the link for a few more words on alternative BRDFs in P5.