Need some advice on a graphics issue

Is it possible to stop spell scrolls from lighting their surrounding environment? For instance, on my slow somputer (128mb graphics card), it gets pretty frustrating when casting fireballs/banish evil because as the fireballs charge or move in a room/area they cause the surrounding environment to be lightened. Is there a way of disabling this? Needless to say, i can't have a torch or light spell scroll up at any time; game goes on 0.2fps