LED vs HPS...LED vs LED...HPS vs HPS...
None of it matters. And gavita can say whatever about the leds they tried...they clearly, and conveniently, leave out the details of the tes(PPF/area/wattage/everything)that would show what they saw what they saw.
But if you want to see a real test is...
PPF vs PPF...that is it. Nothing more, nothing less.
Doesn't matter where the hell the photons come from. Match the photons...and you have yourself a test.
After that you can account for whatever it took to achieve the PPF, and compare(cost, energy, time, whatever).
But if you want results...then use the amount of light that correlates to the growth needed. LED's are not a magical photons or light...photons are photons.
And with that said...a watt is a watt and produces the same amount of heat regardless of efficiency. Even counting the photosynthesis process...that energy will be released as heat.
And though holland greenhouses can get cold...most denver, CA, and Wa and others indoor facilities are not supplementing heat, and is one of the major reasons for adoption.
If I want head...I will use a very efficient source of heat...not a somewhat efficient light to comprose. Use efficient lighting and heating...efficiency of your grow/facility counts on everything.
I, gavita, and tags have all said near linear to 1000µmols many times. As well as given our findings on saturation levels. All coinciding with the majority of published data.