You have to be a little careful relying on par as the only determinate. Par was developed primarily as a terrestrial plant measurement. Corals obviously utilize photosynthesis to survive. But there is a big difference between terrestrial plants and corals. Primarily that difference can be realized when you look at the penetration of light in sea water. Very little red penetrates sea water to any depth. Corals that are found at depths of greater than say 10 feet cannot utilize red light for photosynthesis because it is simply not present. PAR utilizes primarily red and blue as a part of the measurement. However PAR, because it also uses blue and green in its calculation so it is still a useful number for corals. Just realize it is not as simple as just looking at the PAR for coral growth.
For example, if a light has a lot of blue and very little red, is PAR value could be lower than a light that has less blue but contains red. However, the light with more blue will likely grow corals, naturally found at some depth, better than the light that contains less blue and more red.
Something of a side note: algae is generally found near the surface of waters and utilize yellows and reds for photosynthesis. As a result running a light with more yellow and red can tend to grow algae better than a light without yellow and red.
