CFM Guide to Cool Lights

Anyone have a general idea of how much is too much and how little too little when it comes to CFM's in your air cooled light ?
(example)
would 171 cfm 4in. inline fan on a speed controller be sufficient to cool a 800 watt light? or should i get another 6in. vortex fan and somehow adapted it to my 4inch slotted air cooled hood...?

you could do a test run with the fan you have, holding your hand near the hood's glass shield. if it's still puttin' off serious heat, add a fan

yeah, but using your hand won't be a good gauge, as the radiation that warms your hand won't be affected by cooling. 171CFM is not a lot, but if you've already got the fan, test it out and see how the temps turn out near the canopy. Considering that - unless you're using CO2 - you'll want ventilation in the grow area anyway, you can probably pull that off no problem. BTW - where did you get an 800W light? I've never seen those.

haven't purchased the 171cfm fan yet, but was considering since its only going to be cooling my light, (Sun System Vii ) dual 400w. one MH one HPS! Co2 is going to be used and a 6inch vortex will be exhausting my sealed cab. just was wondering if there is a guideline to follow when adding a fan to a sealed air cooled hood w/ glass lens....

if you're going to use CO2, I would get a more powerful fan, as you need to pull all the heat out of the lamp, since the grow area is more or less a closed environment. when the plants get hot, their pores close up to prevent release of moisture. this also has the effect of reducing CO2 uptake. you can overcome this to some degree by using CO2, but it is still optimal to get the temps down at or below 80F.

i have a 6in inline vortex on my 600 watt air cooled light. It pumps out 430 cfm and i keep it on medium. It only cools my light, drawing cool air in from outside the box.

I'm not sure 171 cfm will be enough for 2 bulbs.

ok than its official
thanks all for the feedback, will be gettin another 6in vortex inline fan for sure.