
There may be a way to do this, but when monsters, NPCs, or PCs fall to 0 or less hp, are knocked unconscious, or otherwise "have their lights put out" there should be a way to easily "turn off" their darkvision or whatever sight they had since they don't have it anymore (death will do that to you). The same for torches in the rain or someone who simply blows out a lantern or candle. The only way I can see to do this currently is by editing the token. This slows combats down.