I have a 4 in inline running into the side pushing fresh air a 4 in exhaust with carbon filter pulling from the top ,inside is white, and have a couple holes in the very bottom for free flow air.
What cfm is the 4" fan? I have a 45"w x 21"h x 70"h cab with a 170cfm 4" fan that I was running at 1/2 speed with temps staying under 78*F while I was running 3 240w LED lights. However, I had to turn it to full after I added (4) 2' T5s and (4) 23w cfls yeehaw! Ok,let the flames begin from the LED purists
I agree with the scrog comment, an even canopy would make for much more efficient use of the LEDs, but I still probably would have added the T5s in the corners as they tend to get pretty shady. Here's a pic of my ventilation setup, you would need use a smaller carbon filter, like the CAN2600. It is conceivable that the 4" fan has enough ass to pull through the filter , then push through the light, then out the cab. However, unless you are going to be watching it all the time, do you really want a HID heat source in an enclosed space? if you lose the fan, you could have real troubles bro IMHO