The plants on the outer edge of my tray are not doing as well as the plants directly under the light. How do I fix this problem?

This happens when you are spreading your light pattern to far. There are a couple ways to fix this; you could add another light, you could rotate your plants, you could make your area smaller, or you might even try a different reflector. It can also be caused by over crowding, but that would effect all the plants that do not have there own light instead of the plants on the outer edge.