Quote Originally Posted by psteve
Almost any CFL will have enough of the correct spectrum to grow good cannabis.
I have seen the greatest success with 'daylight' (5000 - 6500K) bulbs. They have a broader spectrum than other CFL's, and can actually be used in both veg and flower with good results.
Well, take a look at this chart and notice how more than 1/4 of the light from a daylight bulb is the green area, which of course is useless for plants, but makes them look nice-n-green to humans. On the other hand the grow bulb has only 14% of it's light wasted on the green spectrum.

While daylight bulbs are great for the vegetative stage, they have much less of the desired red spectrum needed to produce big, dank buds. Notice how the daylight and grow bulbs have virtually identical amounts of nice blue vegging light, but the grow bulbs have six times more of the red spectrum that is sought after by serious growers for budding their plants.

So the deal is, both daylight and grow bulbs will produce almost identical vegetative growth, but a grow bulb or any bulb that has most if it's spectrum concentrated in the red wavelengths will completely annihilate a daylight bulb when it comes to how the flowering stage turns out. Most anything will veg, but the flower stage is what's important. It's all about yield. So for the people that skip the veg stage, the outdoor bulb would be completely the wrong choice.