It's pretty simple, you either have the right number, power output and color of LEDs or you don't. 150 - 1 watt LEDs mixed white and blue give the equivalent of a 500 watt metal halide. But with 10th the heat and 1/4th the power requirement. Will also burn for about 50,000 hours.
Yes, they make fixtures that cost thousands...I bought the $200 panels of 150 LEDs each for $200 per panel off of ebay, posted the link earlier. Been running a year with no issues. Don't have clams, but have both soft and hard corals growing fine,