kevinpo
Expert
It's mainly about PAR not so much spectrum when you are talking about bulbs that are marketed for aquarium use. Past 3 meters of water depth the majority of light is going to be in the lower half of the nanometer range so this is the light that would be utilized by LPS corals.So do the lps also do well under the 20k. right now I am running 250w 20k de with 2 96w 50/50. I had all actinics in there but was afraid the spectrum was to blue. I liked the look but was afraid of the effect on the corals0.
As Anthony often says "form follows function". LPS corals do not occur in shallow water high energy environments. The soft large polyps would be torn away during the first wave set. Since they are found in deeper water they do not require the high PAR readings of shallow water SPS corals. Many exhibit better color using fluorescent type lighting rather than halides for this reason. With high PAR halides they can become very light in color (bleached). While not necessarily unhealthy they don't look as nice (IMHO) as when they have darker/more intense color.
Regards,
Kevin