If you're going to have just 3 corals, clams, or anemones in the tank, I'd get the 30 degree spread (these would also be good for locking and anem into a specific location. The spread would depend on how much you want to 'spotlight' each light point and the distance from the surface of the water. What Evilc66 fails to concede in his lengthy diatribes about LEDs is that if you get the LED close enough to the surface of the water, the (<2") you don't need to get the native 60 degree more focused via a lens. You'll see the spread becomes 50% tighter focused if the get the light right above the surface of the water. If the 80 degree 'bulbs' do not include lenses (colimiters) I'd get that one. The lenses cut the 10% of your light output, which is a big deal when you add up how many of these things you'll need to get as much par as a metal halide.