There are very tiny differences in spectrum and lumens between the various Phillips CMH bulbs. The All-start runs on a MH ballast, only uses 330 watts but has less red spectrum and lumen output, the retro runs on a HPS ballast, consumes 400 watts, has more red, and more lumens. I really don't think that these minor things make much of a difference in the finished product. They are still FAR superior to standard MH and HPS bulbs in both stages of plant life... They are better than the specialty Grow-Bulbs and at about half the cost, twice the life and virtually NO lumen or spectrum loss. Plus, they don't "throw" as much heat. I know that the Phillips is way better than the GE on paper at least, and Im about to find out if it actually outperforms it. I will keep you all posted.