From here: http://boards.cannabis.com/indoor-gr...growing-2.html


Any light will grow weed, but how much do you want for your efforts? Most all the CFL lights you will find in stores are 2700K. These are reddish, and the second best wavelength for budding, and about half the price of bluish bulbs for vegging.

Ultimately you want a mix ratio of about 85/15% in both veg and bud, but that's just tweaking it a little and not necessary.

Vegging (blue):
first choice: 5700K
second choice: 6100K

Budding (red/orange):
first choice: 2500K
second choice: 2800K

These numbers give your plants a chance at peak chlorophyll activity. Until someone shows me a better way, this is how I will determine what K of light to buy. Also notice from the graph that numbers in between the first and second choices drastically cut down on chlorophyll activity.

I would not look for the bluish bulbs in your stores, unless you happen to have a light bulb store or a hydro shop close by. The best way to find the proper numbers for both veg and bud bulbs is by searching the internet. You can get some really powerful ones this way too, much bigger than in the stores.

Look on the manufacturers web site for their spec sheet and compare it to the model on the bulb, or call them. If it doesn't say anything on the package about daylight, or cool, or K, then it almost certainly is 2700K, the cheapest and most common.