My comment's too long So: Basically agree with most of what elPlloLoco says. Here's a little more info:

@elPlloLoco: "1000 micromoles" technically that's 1000 microEinsteins; an Einstein being a mole of photons: . No complaint here, it's just one of my favorite units, and I'd like to see it used more. I run my winter growth chamber at about 500 µEinsteins (half sun), and it works pretty well for full sun plants. Temperature is a problem when you get it that bright. 2fot by 4 foot using 5 2700°K screw in fluorescents, and a 100 watt HP Sodium lamp. Cooling fan is essential. The shade plants like to be under the top wire shelf, so probably somewhere around PAR 200-250, as elPll says. When buying lamps, people tend to emphasize blue too much. 400nm-700nm gets both photosystems nicely: All the extra low nm blue does (Hg line) is heat and dehydrate things, and burn your leaves.

My comment's too long So: Basically agree with most of what elPlloLoco says. Here's a little more info:

@elPlloLoco: "1000 micromoles" technically that's 1000 microEinsteins; an Einstein being a mole of photons: . No complaint here, it's just one of my favorite units, and I'd like to see it used more. I run my winter growth chamber at about 500 µEinsteins (half sun), and it works pretty well for full sun plants. Temperature is a problem when you get it that bright. 2 foot by 4 foot using 5 2700°K screw in fluorescents, and a 100 watt HP Sodium lamp. Cooling fan is essential. The shade plants like to be under the top wire shelf, so probably somewhere around PAR 200-250, as elPll says. When buying lamps, people tend to emphasize blue too much. 400nm-700nm gets both photosystems nicely: All the extra low nm blue does (Hg line) is heat and dehydrate things, and burn your leaves.