Is your light a fan cooled?In the closet all the heat will stay in the closet.
vent it out of there.Old air out new air in.I have an 2' wide by 8' long by 8' high closet and the 400w light heats up the room to around 90* with the door crack open and higher closed.Bring in fresh air and circulate it around
the closet.Vent the old air out.It just like we do {breathing} in with the good out with the bad.You can get lights with fan vented,I use a sun-2 with a 6"
vent and a 6" vortex fan to cool the light down and vent the hot air out in the attic.Hope this helps you .