tested on a new fresh scene, using soft 2012 x64bit SAP. Its not working unless i use sphere or cylinder. Yay more bugs

disc, object and rectangle area lights with physlight and blackbody.

this is si2012 sap, but i tested this also with si2012 and it works.
could you send me your clean testscene, so i can take a look?

here it is

It works here too, I use point light, maybe that makes difference?

switchin to point make it works but it gives a total weird output, like if the light is coming reversed, from the opposie side of the light itself..

ah, ok, now i see.
you used a spotlight, that does not work. its the same like in vray, spotlights does not exist in real world as a lightsource. use pointlights for this and it should work.

also use a cone value of 0.5 for example.

edit: also, you have to look on the z direction of the light, thats the light direction.

alright thanks for clarifing, now it works
Gotcha

Ahh Mental Ray

the whole physical stuff needs to be implemented as presets and documented with some examplescenes so the users know that it exist and know how to use it, but yes, thats mr (integration).