Hi Egon,
It would be great to have anti-lights (I can't think of a better name - 'Darks' maybe?) so you could have areas of darkness even though the ambient light level was high.
I'm trying to make a large, well lit area with some dark patches. Currently I'm having to use lots of lights with carefully tuned locations & attenuations. It'd be much easier to set the ambient light level and have 2 or 3 anti-lights... Is it possible for you to put in lights with -ve intensity? Would it be the same code only subtractive?