3x600w cool tubes in 2x2tent - how far do i need from top of plants?

i have a 2x2m tent and im running 3 x 600w cool tube lights fully ducted up with an extraction fan.. i was just wondering, how far do i need these from the tops? i can practically put my hand on the glass its that cool just under them.. i have them at about 18 inches now, was thinking they could go a little bit closer??? at

I've heard about 6 inches with a good cool fan. Hold your hand there for a minute or two and you will know if its too hot

I used to have my 600W at 18-22" before I got a cool hood on it, after that I had no problem keeping it at 10-12" witch according to my light meter gave me +5,000 ft candles even at the edges and more like 7K at the center of the light (picture from before I got a cool hood)





here is a chart that show how much a HPS emit at different distances

View attachment 2940186


according to my cheap light meter the glass on the hood do block 10-20% of the light so to speak, but as you can keep it like at half distance you get more Lumens to your plant`s

I would drop to 12 and see how they react. Light blea hing etc.. With that many lumens in a 2x2 area I don't think you need to get closer. JMO

Like to see how these turn out. I just put 2 600's in a 4x8 with a light rail.

im running another 2x2 with 6x400w in normal hoods and have to keep them way above the top. have lowered the tubes down to 12 onches above and am going to keep an eye on it. the fan i have on the system seems to be doing its job well, i can put my hand 6 inches under with no real heat.