a 400 is going to get hot and raise the temps in the room atleast 8-10deg. if you try and exhaust the air right outside the cabinet it will still be fairly difficult to cool the air goin in because you are sucking in warmer air. i at first tried to exhaust my cab into the same closet as i pull air in and the cabinet stayed cool but not cool enough. i had to cut a hole in my wall between the bathroom and closet and that brought my temps down another 10-15 deg.

so temp without aircooled light was about 100-105
temps with aircooled light exhausted into same area as i am pulling in fresh air 90deg
temps with aircooled light exhausted into bathroom(another room)75deg

your temps wont be as high because you are using a 400 watt instead of a 600 watt and you might have a cooler area naturally but i would recomend an aircooled hood exhausted to another room