I used to recommend Aquamedic's Planta bulbs, but do not anymore. They grew plants great at first and gave off the nice color that you might get from an 8,000k bulb. However, they grew dim and lost their effectiveness after only 5 months of use. These bulbs were appropriately used (read: not overdriven) in a 48" Tek fixture. Apparently Aquamedic's products that are sold in the USA are not of the same quality as those in Germany as they are made in China.
I would stick with the Gieseman bulbs for now. GE makes a daylight bulb also, but I do not have experience with that one. I thought Gieseman had a 10,000k bulb too? Oh, and for good prices and service try www.reefgeek.com
. I hope that helps you some.