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 6ā?), 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 4ā? x 4.5ā? grow area, and you say, ā??Well, it's close to 20 sq. ft. so I'll get a 1000w HPS...that's about 50w a sq. ft.ā? 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.