Opie is correct. A sealed air system for the light is proper cooling. Passive may work if you suck the air out through your cool tube with a large enough blower.

Cool air in from the ground level and hot air out at the top.

But it's better to have your light system sealed and have a blower outside the grow area and use dryer vent pipes to connect all the air from the blower to the light then use a second piece of vent tube to take the air away from your plants.
Zandor Reviewed by Zandor on . I need help now!!!! Well I spent the whole night awake watching over my plant. My 400watt hps showed up so I threw it in and wow did the temps ever sky rocket. My cab is usually about 73 or so in the dark and with the cfls it was usualy around 78. With the hps now they jumped to 90!!!! I know this is ok but I'd really like to drop it to a more manageable level. What's the best way to do this? My cab is 4x4x2 I have 2 fans inside moving air around and a squirrel cage fan off of an old hockey table. Would Rating: 5