They are a low kevin bulb. Mostly for BLOOMING or FLOWERING.
Kelvin is a measure of temperature, as in 5100K or 2700K (this is the emitter temperature, not the actual temperature of the bulb itself), and it refers to the color of the bulb; 6500K being a blue light spectrum, and the 2700K being a red spectrum. Plants like a predominately blue spectrum during their vegetative growth and like red spectrum light during flowering. Together the 6500K and 2700K provide a dual, or complete spectrum, suitable for all plants during all phases of growth.
IT IS POSSIBLE TO GROW ONE PLANT WITH ONE LITTLE 26 WATT CFL BULB, I;'ve seen them here on RIU. But, the more watage,the more lumens, and the more lumens, the FASTER and BETTER they grow.
I use 4 65s, 4 85s, and 4 105 watt CFLs on an average of 8 plants and they grow SUPER FAST, with a low electric bill and very little heat.