Real world lighting.

Hi. People who use VIZ Render or 3DSMax know this software, when working with lights, asks the user to input values that correspond to the physical world values that can be measured in real life (that is, intensity in cd, or luminous flux in lumen, or illuminance in lux, especially for daylighting it will be varying from a 15000 lux or so in a bright midday to a 8000 lux in an overcast situation and so on and you can actually input this value in the software).
Now, Blender has unitless values. So how do I understand what value I need, do I have to tweak and try (time consuming, not precise) or is there a way to determine what physical situation I am reproducing in the renders?

Great that someone asked that question! I would also like to know the answer! I always had problems with setting up the lightning.

…erm, anyone has got an idea? Or is the question unclear?

It’s pretty much guess and check and you get better/faster with experience. I don’t know of a version of blender that has units.

Anyone knows what are the VIZ render values based on? I mean, how do they manage to make those values correspond to a realistic lighting intensity? If there is something like a “scientific” way to do it, then it should be implemented with a script or something in blender!