experience with Metal Halide?

[naoki]

Thanks for the info, Joseia. According to simple calculation here:

http://www.aos.org/Default.aspx?id=516

the conversion between intensity under constant light vs natural light is about 1:2. So the sun light with 2000 fc peak intensity gives similar cumulative light as 1000fc constant light.

So 700fc of MH gives about 106 micro moles/m^2/s of PAR, which is equivalent of sun with 1064fc peak intensity. I guess that your example shows that you can bloom orchids with way less than what is recommended for greenhouse growing (and those hypothetical calculation isn't enough). For example, with artificial light, you can give a longer day to compensate for it, or you never have cloudy day.

Here is the conversion table for foot-candle vs ppf for the calculation:

Conversion - PPF to Foot-candles

There are high performance LEDs (which can even come close to HPS efficiency), but the initial investment is still quite high.