A lot of people are passionate about their plants, and they get an early start on the season by growing seedlings indoors when outdoor temperatures are still low. Many of these people look to 6500K CFLs as their solution.
We thought we'd take a moment to explain light bulbs used for growing plants; to mention what options you have besides CFLs; and to showcase our own selection of 6500K CFLs.
Traditional wisdom in regards to light and plant growth is that cooler color temperatures (more blue wavelengths) assist with seedling growth while warmer color temperatures (more red wavelengths) help with the flowering process.
Based on this, if you're planning to move your plants outdoors when the weather warms, you can focus on lamps (lights) that emphasize blue wavelengths. That means lamps with color temperatures of 5000K or up, and especially 6500K lamps.
What many people don't realize is that even these lamps will have some of the warmer colors (red wavelengths) within their light, and may still help plants with flowering. However, those who grow plants from seed to flower indoors typically recommend full spectrum lamps or a mixture of high and low color temperature bulbs. (Full spectrum and "grow" lights are fairly expensive, though, and people have plenty of success by mixing color temperatures to create their own "full spectrum" effect.) Based on reported results, we would suggest perhaps two 6500K lamps for every one 2700K or 3000K lamp; some people simply use a 1-to-1 ratio of these two color temperatures.
As for lamp types, CFL bulbs aren't your only option, but they are a popular choice because many of them have a standard ("medium" or "Edison") base that screws into fixtures most people are familiar with. Some, however, will choose a shop fixture for fluorescent tubes, or may even upgrade to long-lasting LEDs. It's generally recommended to not use incandescent or halogen lights because of how much heat they emit. If you do use these, make sure to set them further from the seedlings.
If you do stick with CFLs, some experts would recommend using reflectors to help provide more even light across all the seedlings and from all directions. This is true with tubes as well, but their length across all plants (on a shelf, for instance) may already help in balancing out lighting.
In some cases, LEDs are programmable and could be made to provide sunrise and sunset effects for plants. Given the success people have had without such advancements, though, it's unclear how much value this would offer for the additional cost. Importantly, though, any light used should be on a timer rather than left on continuously. The amount of time may vary by plant and brightness of the lights, but a rule of thumb for seedlings is 16-18 hours a day of lighting.
If 6500K CFLs are your lamp of choice for seedlings, we offer several to choose from, including the most likely candidates pictured below. (Click on an image to see it online.)