It is simply a measure of how much visible light output is produced per watt of input, regardless of lamp or emitter.
No, it's not.. it is the amount inside a subset of visible light.
Splitting hairs? Maybe.
Metal halides produce more visible light per watt,
Can't see how you come up with this. Do not use lumens.. :)
Leds emit no or little UV/ IR . Almost all watts go to heat or vis photons.
Since "PAR" is the total of all photons from 400-700nm with no discrimination or weighting of any individual "color" it is the de-facto standard one should measure efficiency by.
Unless one is making a germicidal or heat lamp.
As to a "watt is a watt" thing yea.. after the photons are converted (well what happens to the few percent consumed in photosynthesis) to heat sure a "watt is a watt".
Initially though leds produce more photons/watt than a MH or T5.
(Qualifier: equal or more if using average to above average LEDs ) current leds, old ones had "lumens" in the 50's and were only "saved" by very sharp focusing as to not "waste" any.
So less heat.. initially. Not NO heat obviously.
Royal blue is THE MOST efficient led out there.
And phosphor whites based on rb is the same.
It wasn't till recently that one was even considering the weakness of violets or UV chips.
Even though LEDs can be more targeted, halides emit a broad, continuous spectrum, and some of those wavelengths may be critical for coral health, coloration and other biological effects.
Good hypothesis, now for proof...:)
See I personally don't believe there is a "chasm" between the 2 light sources. If one is better or worse its baby steps not orders of magnitude.
As you know in my history that I "feel" that Iwasaki mh's were excellent bulbs that easily exceeded any LEDs in characteristics.
Even against other MH bulbs.
Too bad most find them ugly.
It's a hobby for enjoyment right? Not a business.
Why? Actually MORE blue (percent wise) and more "par" then even the bluest bulbs.
I also assume few if any ran high wattage daylight arrays of leds preferring RB and dimmed high k whites ( a bane of my existence ).
Not to mention the lies of equivalency sold to the public. or the horribly efficient TIR lenses.
Anyways that's off topic.
I have no issue w/ finding out if things like UV-b (not likely) or deep IR is beneficial over leds with none. BUT give me proof.
5% better.. .005% better ..50% better...?
People want to quote nature.. Why?.. Shes trying to kill you at every turn. Best you can do is put up with it.. :)
Because something can survive something does not imply it's beneficial.
Just because..
LEDs are full spectrum if one ignores UV/IR. Old school pfo solaris..
https://www.saltcorner.com/Articles/Showarticle.php?articleID=141