I saw that video. Please point the minutes..
Grandis.
He spends quite a lot of time explaining how PAR has limited usage, PUR is malarchy, lumems is more about just whats visible and PAR is also an outdated measurement (from the 60s) based on whats VISIBLE and usable in agriculture......not designed for aquaculture at all.
Spectrum doesn't get enough conversation.
The spectrum on Kessils are near perfect and 90watts of power is 90 watts of power...all in exactly the right spectrums. The Hydras can get close if tuned right as can Radions.
He very clearly states a few times that PAR meters are zeroed/calibrated in a T5 standard which does not measure the sane as LEDs.
He also explains very clearly that MH, T5s and full spectrum lights all give off usable photons but are less efficient as the corals do not utilize certain ranges of those photons...although this varies from coral to coral they are overall giving off wavelengths that are not very usable to many corals yet register higher both to the human eye and an a PAR meter.
This is similar to the original Kessil explanations but it's worth it to watch the whole video.
LEDs are subject to burn corals due to lensing and must be turned down, but that can create problems for corals deeper in the tank and THAT is the fundamental challenge with LEDs.....not the PAR standard from the 60s. They do have superior spectrum abilities as they can be turned to the precise needs of corals with no wasted extraneous energy going to spectrums which are not used.
Shadowing with acro is also a problem w LEDs which he did not touch on at all but he did a good job of convincing me that some of that same shadowing occurs in nature anyway as well.