No practical way to measure spectrum, other than by looking at it. You can tell a big difference between the light a daylight bulb makes and a soft white, like shining them on a white wall. The soft white will look reddish or orangeish, and the daylight will look blue. I can tell a 4100k "cool white" tube because it looks green. It's a subtle difference, because overall they're all white. But if you put two different bulbs back to back, you can tell. You can't do this in stores of course, you have to plug them in. I noticed while browsing the bulbs in wal mart that: a. they don't sell the conical spiral 30w daylight Lights of America bulbs anymore, which sucks cuz they were my daylight of choice, and b. a lot of the new GE and phillips packaging doens't share color temperature, adding to confusion. At least they still say soft white or daylight. I also couldn't find any more 65w flood lights. I owe LoA an appology, bad mouthing their bulb's quality. I thought my 65w was broken cuz only half of it lit up, but it just takes a while to warm up. I will be putting it back in action soon, 65w for 6825 lumens at 6500k. Nice bulb. Could do a small plant by itself.
If you're just going to be doing 1 or 2 plants, 100-200w of CFLs is all you'd need to get all the way to bud. And if you're going to just be vegging, probably 50w of daylight CFL's would start 4 plants pretty well. But if you're flowering under them, I recommend finding the biggest wattage bulbs you can and getting at least around 100w per plant. It's such a long road to buddage, you don't wanna skimp on flowering ya know? 100w of CFL's will probably keep the plants plenty warm if they're close (as they should be). Again, still not sure on color temp for flowering. I think I'm going to change out the remaining soft white for similar wattage of daylight in my grow, because it's an important question and I want more definitive results. I gotta get outta here...
