The spread is pretty good... I have a 24x18x18 ExoTerra that is lit just fine with a single LED. The spotlight LEDs are different though. Here are photos of my racks lit by LEDs:

20 gallon verts 1 light each:


18 cube and 24x18x18 1 light each:


36x24x18 2 lights:


36x18x18 2 lights: