Help me out with acouple lights questions ondimmer switches

would a dimmer switch on a 1000w hps light make it have the capibility of working at the same level of a 400w hps light..... beacuse i have a 1000w light but its too big for the room im in you think this is a bad idea?????

Don't see why not, not sure how you'd know when u were at 400 tho?