Better yet I know of lot of folks read this so I'll cut the middle man for the lazy folks
Color Temperature
You might see a lot of different labels when shopping at the store for CFL’s. Label’s including Soft White, Warm White, Cool White, Bright White, Halogen White, Daylight White, Full Spectrum. And also label’s like 2700K, 3000K, 3500K, 4000K, 5000K, 6400K, and 6500K. These are all the color temperature of the light you are using. This is a measure of how warm or cool the light given off by a lamp appears, with warmer colors having a yellowish tinge and cooler colors being tinged with blue. What confuses some people is that the warmer a color is, the colder its color temperature is. (ex. Warm White = 2700K). Bulbs ranging in the 2700K-3000K spectrum are usually labeled Warm White or Soft White, bulbs ranging in the 3500K – 4000K spectrum are bright white or cool white, 5000K is labeled Full Spectrum, and finally 6400K – 6500K is labeled Daylight. You can grow an entire crop with CFL’s if you chose the right spectrum of bulb’s. For Vegetation you will want to use 6500K or 5000K, and when you flower you will want to switch to 2700K or 3000K . The reason being, throughout the year the plant’s outside receive more 6500K light because the day’s in summer are long and hot and as Autumn/Winter get’s closer the day get’s shorter, and gradually receives less 6500K light and more 2700K light as the plant flower’s. Do what you can to avoid bulbs within that 3500K – 4000K because they emit very little light that Is useful to your plant. Notice here the difference between the CT of these lamp’s