i'm stuck here too
So... I got onto the ledge and i switched the lights off, I know what I must do to get across the room BUT decided to save at this point - waited on the ledge just to see what happened and the lights came back on - now the switch is useless, i cant switch off the lights again to move on through this part of the level and i've no savegame before entering the room to go back to.
Can i flick this switch a second time somehow? or will i have to resort to the notarget cheat? Ne help would be great.