you can edit brightness of scene or use lightmap I think.
getObject["Scenes[scene_name]"]:setValue(VSceneBrightness, int) -- add number between 1 & 100
but you can change scene brightness via actionparts also; either via "scene" or "miscellaneous" I forget which section.
P.S: you've just reminded...
could David or someone add a global scene/game brightness setting?