Build an air cooled hood for your light. I am assuming that you are using a MH or HPS light. This is a fairly inexpensive route to go and it can greatly reduce the temps in your area just vent the light into the room.

If I were you this is what I would do.

Go to Home Depot and buy the cheapest door that is the same measurements as your closet door. Then take the appartments door off, put the new cheap one on.

Now, cut holes for intake into the closet into the bottom of the door. Cut a round hole (probably a four inch) into the top of the door. Mount a 4 inch duct fan, available at Home Depot, into the door, connect it with tubing to your now modified air cooled hood and vent the heat built up from the light strait out of the room via your new ducting.

I hope that made since. If you want me to be clearer on anything just let me know and I will gladly help.

Take care.

Peace