i believe PAR38's can be used as standalone lighting with no issue's the key here is to find the right blend of LED's wether it be warm white, Cool white, Neutral white, Royal blue, cool blue, or a mixture of all 5 maybe nesscessary to achieve 100% results but from what i've seen on my own setup PAR38's by themselves can grow and keep coral just fine
The only issue i see is with color and color doesen't nesscessarily mean that a coral isn't healthy or thriving, it's only for personal appearance and enjoyment that corals have vibrant colors
I'm getting 4 custom PAR38's made right now with 1 neutral white led and 4 cool blue leds per lamp, IMO these will help to improve the coral color but it will take some time with these over my tank and corals to gauge this, i'm trying my hardest to get to the bottom of coral color's and LED's role with them
So if the custom lights i'm having built solve the issue of color, than i think the T5 and MH fans will be switching over sooner than later
I've always been a fan of T5 and MH and from what i've seen LED's can do the same exact thing as those setups but for a lot less heat and energy consumption, upfront cost is the only difference between the two