The par38's are nice bulbs, the only down side is non dimmable...and with 40 degree lenses at around 14" off the water they cover about a 12x12 area. Great if you like the spotlight look. Evilc66 has a nice thread on his tank. Last I looked he was running 5-6 on his 75, I liked the spotlight look. For good coverage on a 10g you would need two bulbs.