If you ever made maps or levels for Half Life or Unreal engine 1 games, you've certainly faced the "green tint" issue regarding lightmaps. It's something caused by a limitation of bits in lightmaps. RGB (Red Green Blue) as we know form a triplet of three values which range from 0 to 255. That's 8 bits, 256 possible values. Do the math and you have 256 to the power of 3. Which results in the millions of colors that our human perception can see. In older tech there is a limitation regarding how the colors are stored and when we have very bright lights, the excess, the brightness that goes beyond certain values, is clamped. Every color is a vector with three components, one per primary color. The "green tint" effect is caused the that values of each component being clamped such that there is an excess of green left.
I wrote this more than a decade ago. It covers the theory behind hint brushes and occlusion in the days of Pre Computed Visibility tests. This should be now obsolete, because with the current complexity of game scenes and the extra power with modern hardware. Visibility and occlusion can be handled in realtime, without having to manually place portals. I can assure that PVS was more suited for indoor worlds, much like Quake. It was also a huge time consuming task. I put it here for study / historical reasons.