Would be fine with a cooltube. You can recover some of the intensity lost by the 24" uncooled recommended spacing by installing a cooltube and dropping the light to 330-350mm (12-14") min clearance.
For good density, I use the coarse (but darn close for 400, 600 & 1000HPS) guide of 50W of HPS/sq ft. For a 4x4 table, a 1000 would be best suited per that rough guide. A 600 would produce nice results too, but you may want to move plants around in the trays periodically to even them up a bit. Plants left always on the fringe of the light coverage may not do as well as you like.
However, most horizontal tube reflectors lay down a mainly rectangular light pattern. This is why I use square tables in pairs, to create a rectangular plant space to be covered by a single 1000 in a cooltubed batwing. Of course, you can buy rectangular trays if you like.
True. Cooltubes trap quite most of the radiated IR but not all of it. I can lay my hand on a cooltube running a 1000 and leave it there but I don't think I'd want to do it for 12 hours straight, nor would I lay a plant up against one. I don't have a surface temp thermo but the warmest part of my cooltubes would be close to 38-40C. The cooltubes are so effective at ducting off heat from the HPS bottles and my room air circ is sufficient enough that the air temp (measured with a light-shielded air probe) under my batwings is just the same as any other place in the room.
Mmm. Pretty big table for a 400. I'd probably choose a 2' x 3.5'-4' tray for a 400 in a horizontal reflector.
If I'm not mistaken, those figures are for lamps without cooltubes. Easy to cut any of them in half with cooltubes installed. I wouldn't feel bad about a 400 in a cooltube at 6-8" clearance. You can use the inverse square math to adjust the intensity figures accordingly.
Nice drawing.
Not sure about the round tray (is that what I'm seeing?), though, unless you're using a vertical tube 'chinaman's hat' type reflector, which are not the most efficient sort and their tube sockets run very hot, reducing lamp life.
If you want to do a grow in the round, think about a vertically mounted cooltube column. I've seen a 'stadium' or 'coliseum' grow which used a pair of 1000s, in seriesed cooltubes, like my setup, but with plants on 3 levels of shelves surrounding the cooltube column. I like the fact that all light in such an arrangement comes straight from the lamp tube instead of half of it bouncing off a reflector before it gets to the plants.
peace
