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I never said it was the best way to measure how much light you HAVE.Quote:
Originally Posted by Roughrider
As I said, it's just a quick and easy ballpark estimate.
You don't want <50w/sq.Ft.
If you have >50W/sq.Ft. of CFL or HID, you are in the ballpark where it is possible to grow cannabis.
Many (most?) CFL bulbs do not even put the lumen output on the package, making it quite hard to use lumens as a measurement.
No. 50w/sq. ft. is not ??in the ballpark? for HID. Take a 400w HPS light that puts out 50,000 to 58,000 lumens. That will cover a 10 to 12 sq. ft. area very well. That's 33 to 40 watts per sq. ft. ... and that's giving you a very good grow. That amount drops as you get bigger bulbs...when you're at 600w (80,000-95,000 lumens) for instance, it's down to 31 to 36 lumens per sq. ft. So you can easily get by with 20-30% less than 50 lumens per sq. ft. with some HPS lights.
CFLs, on the other hand, almost uniformly put out 65 to 70 lumens per watt. They don't become more efficient at larger sizes like CFLs do. A 600w CFL is twice as efficient as a CFL, so using watts means you'll be off by 100%. That's a lot. 35w per sq. ft. will give you a terrific grow with a 600w HPS. To get comparable lumens, you'd need 70 watts of CFLs per sq. ft. (And, honestly, lumens are more available on CFLs than kelvins...because CFLS like to note incandescent equivalents, they usually put lumens on their packaging)
So, again, using watts is a very, very poor way of judging how much light you need. You can do VERY well with 40w sq. ft. with a 400w or larger HPS and have fewer accompanying heat and ventilation issues. On the other hand, 50W per sq. ft for a CFL is 3500 lumens per sq. ft.; very mediocre. You need to bump the amount of lumens by 40% to be in the very solid area. Different lights = different efficiencies. Don't use watts.
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Very interesting, mostly true, but irrelevant.Quote:
Originally Posted by Roughrider
I personally know dozens of patients right here in Oregon who are growing fine medicine right now using >50W/sq.Ft.
Unfortunately, it's completely relevant. The idea that you can take a decent plant through flower and get a good yield with two 26w CFLs is, sadly, untrue. That's more than 50w and unless your plant is small (we are talking about going into flower at maybe 6?), it's just not going to be enough to do a good job. You'll need to keep your plant in an area of well under 1 sq. ft. You can get something out of a plant like that, but but you're selling yourself short and wasting your time. You need more light to do well..
And, on the other side, saying you need 50w per sq. ft. with HPS can cause you to get more light than you really need, and that is a big factor in heat and stress issues. If you've got a 4? x 4.5? grow area, and you say, ??Well, it's close to 20 sq. ft. so I'll get a 1000w HPS...that's about 50w a sq. ft.? you are getting more light than you really need. A 600w HPS with a high output bulb puts out 90,000 lumens or even more...it will do fine in that area, used 40% less energy, and give you less heat and ventilation issues.
Because of the differences in efficiency between CFLs and HID lights, and because of the differences among HID light efficiency at various sizes, wattage does not give you an accurate idea of light you produce. And it shouldn't. Watts have nothing to do with light; they are a measure of energy used to produce the light. You can get as much light from a lower wattage bulb that has higher efficiency. Which is why using lumens is always going to be better than using watts. It doesn't mean that using watts will always be wrong...but it is going to be wrong a good amount of time, and wrong in ways (not enough light, extra heat) that can cause real problems. Is that really worth it? I say no.