wordwiz

Velutina,

I don't disagree with anything you say but I want to clarify the way I use lights. For seedlings, I use CFL almost exclusively, though if I need a bit more room I turn on my shop lights. Works great, produces stocky plants. For plants I want to grow to maturity (read: harvest fruit from) my bulb of choice is MH. I base the height it needs to be not on the area I want to cover but the lux it provides to the plants. The goal is about 30,000. I'm finding a 600-watt MH does a fine job covering a 3.5x4' area with Mylar-lined walls. I probably can squeeze out a 4x5' area if I really need to.

I use the 30,000 lux figure based on studies done by lots of people concerned with growing plants in a Green House. They concluded plants need a certain amount of "mols" of lighting per day (Daily Light Integral) to be productive. For tomatoes, that figure is 22 mols/day. 30,000 lux (2788 Foot Candles) times .000546 gives me the mols of PAR light per hour (1.522). Running the light for 15 hours a day will provide 22.83 mols per day.

Other types of light use a different instead of .000546. For instance, sunlight is quite high: .000718, HPS is a lowly .000543 and a cool white fluro checks in at .000524 (these are for the "average" type bulb - each bulb may have a slightly different factor based on the spectrum). But, if I did my math correctly, an LED blows all these lights away, having a conversion value of .0036. Of course, they produce far less lux or Foot Candles.

For my DC banana, it's under a 125-watt LED. I know it can pretty much cover the plant canopy, at least until the plant is nearly mature. And it is delivering about 23 mols per day!

Mike