I allways put a very big and slightly blue MR area omni in front of every window to simulate the sky light
then use a white-yellow MR area spot light for the sun
never use lights inside (except for decoration light fixtures on walls and sealings, but they never light up the entire scene anyways in daytime setups).
forget about using glass in your windows at first (it’s very hard and rendertime consuming to get light going through glass in MentalRay and have a nice lit interior, i allways composite a scan line glass in the windows afterwards)
first make sure you have your units correct :
a ‘cm’ in your units should represant a cm in real life
this is very important to get your sample size under control
I always start with only a few (2500) GI samples and make them 30-60 cm
make sure you can see the photons on your scene objects (kinda like a flash light shining on a wall)
if you can’t see them then there’s something wrong with the units
once you see them ok, turn on final gather very low (lets say 50)
just to have a quick preview on a 320/240 test render
(should only take a few mins)
to brighten up your scene don’t mess to much with the multipliers!
play around with the energy level (20000-100000 should do) and together with that : decrease the decay (from default setting 2.0 to let’s say 1.6)
just enough to brighten up everything in the scene and have more bounce of the light away from the windows
in my experience it’s a very sensitive parameter, cause when to low (let’s say 1.5-1.1) could make the render go completly white and overlit…
then when satisfied with the result only increase the image size and Fgather untill good result.
tip : :lightbulb when you really can’t find a good setup there’s a very good example scene that come’s with the official max6 install package from the guy’s from KDLAB. Import your scene in that file and that should get you going
here’s a sample of what I got out of Mental ray so far :