[drew51]

Originally Posted by Hermitian

Lumens are a measure of human perception of brightness. There is no relevance to plants. They are only on the label because of an outdated US architectural law regarding light bulbs. What matters for plants is spectrum (6400-6500 Kelvin) and Watts/sq.ft. of projected area. Fluorescent bulbs have an output efficiency (initially) in the high 90 percentile, so input Watts is very close to output Watts.

OK, well it doesn't have the wattage info. Spectrum is as you mention, the growth spectrum, not the blossom spectrum. They are plant lights, T-5's at 4 feet, 4 bulb fixture. It's bright!! I'll tell you that! I do not like looking at it. I can also add more lights, but only 2 footers. Like say a side light for mature plants. Right now the foil is useless as they are just seedlings and the light is very close to plants. I actually have a bunch of old I guess T-8 fixtures. I might use them in the future too, they are being useless at the moment.

So in the winter, use the 6K Kelvin? not the 3K Kelvin lights?