Hydrofarm makes a dual-lamp reflector called growzilla that will take any combination of bulbs up to 2 1000W bulbs.

Why do you want them in the same reflector? Is it just cost?

Actually, I just figured I'd get better light distribution that way. It's for a greenhouse, for supplemental light.

If 2 reflectors side-by-side would work I could do that as well. I just don't know if the light distribution would be as good.

Light distribution would be better in seperate housing IMO.

My greenhouse will be 12 X 22 or thereabouts. I am trying to distribute roughly 1100-1400 additional foot-candles over the majority of the house to compensate for our cloudy dark winters. 2000 W of HPS would put out about that much over a 12 X 12 area when you figure in you'll only get maybe 65% of the lumens with a good reflector. That's why I figure 2 Growzillas spaced 11 feet apart ought to do the trick...maybe I'd be better off with 4 1000W lights 5 and a half feet apart??? What do you think?

From where did you get the 65% efficiency factor for the reflector?

Many of the websites that sell HIDs have a chart indicating that a 1000W system is good for about a 12'x12' area. My experience with 400W and 500W systems in the basement lead me to believe it's close. Outside, even on dark cloudy days, you are going to have some light (more than I have in the basement!).

If you are interested in 1000W dual-bulb system, check out sunsystems. They have a 600W HPS / 400W MH unit. It's a lot cheaper than the growzilla.

I figure 65% efficiency-50% of the lamp faces downward, so that's 50%. The reflector might reflect most of the rest of it down, but a good portion gets reflected back into the bulb.

Do you think it's higher or lower than that?? My Sun Systems IV 1000 watt MH light seems about 65% - 70% efficient if I take the rated lumens divided by coverage area.

I've seen the Sun Systems light-it's not bad and I may use it in my grow room inside, but in the GH I don't know if it's enough-our winters are lucky to break 500 foot-candles at high noon on a cloudy day-and with the glazing on the gh it will be considerably less in there with natural light.

Figures for a typical (ie. obsolete) high bay metal halide lamp are 80% efficiency. State-of-the-art lamps provide 95%+ efficiency. Efficiency is the percentage of light produced by the bulb that actually leaves the lamp fitting. Obviously that light all goes down but some of it may go down at an angle that leaves the side of the greenhouse. I think 65% bulb to floor efficiency is a bit low for a good reflector.

Hmmm...I may get away with lower wattage then if that's the case. What's a "high bay" metal halide? Is that the type of reflector?

"High Bay" is just lighting used in warehouses and gyms with high ceilings. It is a very common use for metal halide lamps and there are standardised lamp fittings for it. Newer high efficiency fittings are rated for 92% of the light going "down".

I see. Of course I've seen those-didn't know they were metal halide though.

Do you recommend a specific brand of HPS that has a good wide spectrum and high PAR wattage??