"Not "quite" correct, HDRI (as used in rendering terms) is a subset of image-based lighting that can have brighter than white lights and darkere than black shadows. This is so the renderer can determine the lighting difference between a sheet of paper, a phospherent light, and the sun."

Tthe use of HDRI in rendering is not just limited to IBL (as in using an image as light source): HDRI is also frequently used for environment mapping (with a bit of shader node magic, you can do that in Poser 5).

Yet, many applications misleadingly have a "HDRI" label on their IBL functions, just like many say radiosity when they mean path tracing or photon mapping.

Every renderer knows whiter than white, they all use floats or doubles for their internal calculations. For example, you can set a Poser 4 light to 10000% intensity for "brighter than white".

"The reason I say this is "not quite right" is that you can have greater than eight bits of colour information and NOT be uing HDRI. For example, using 16 bit tiffs would still be classified as non-HDRI."

Actually, this presentation from the SIGGRAPH 2003 course on HDRI and IBL does list 16bit/channel TIFF as HDRI file format.