150w Bulb in a 400w Ballast

I was wondering if I can change just the bulb, is this safe?
I have a 400 Watt ballast and housing.

just go to Home Depot and buy a 400W bulb.

i think it will work , but your cutting the life of the bulb down massively.

I am trying to reduce the heat in my room.
Addition of a 400w = 800w increases my temp by 10/15 degrees.