Changing the lighting on a token does not change the global settings, but it might look like it to the GM, or to any player who shares light with other sources. Lighting "overlaps" visually, so if two dim light sources are near one another, the overlapped area will seem brighter. Get enough of them together and the dungeon will seem very bright indeed. To see what one token will see, select it and use Cntrl/Cmd-L. If that doesn't answer your question, you might need to post the actual settings of any problematic characters. Screenshots might help.