What I found in my games is that the lightning follows you wherever you go. One time, I jumped the character out of the room with cheat keys, and no matter where he went, the lightning was sure to follow
Actually though, a monk or thief is the best choice. If they make the saving throw, they take no damage. My rogues usually didn't.
And yes, the magic word to reach the anteroom with the shadow door is "Lysan".
Nightowl2