Im in the same boat as far as the heat argument. A light source has an efficiency and produces heat and light.
The argument is always "well all light turns to heat eventually" but I think its the misconception of the term heat in physics since heat can also mean work, which can be biomass in this instance.
That energy is only released as heat (thermal) when its burned (outside our grow room usually).
The other argument is always "energy cannot be created or destroyed" but again if one light can produce 1gpw and the other light of equal wattage can produce 1.2gpw then that extra biomass is the difference in the efficiency of those lights both in electrical efficiency and spectral efficiency from the point of photosynthesis. That is energy that was not converted to heat in the sense of grow room temp rise.
Then we have the issue of different spectrums been absorbed by any material and different material warms at different rates depending on the spectrum.
Im sure a 60w incandescent would heat a space faster than a 60w LED. Then stick a plant in that space which will not really grow with the incandescent but will grow with the LED and the resulting biomass should reflect the difference to some degree between the temp rise of the two spaces.
What annoys me is the constant repeating of the same arguments without anyone proving one way or the other. I have seen it done at grade school level for basking lights (online) but unfortunately not done properly.
Im going to have to wait till one of my tents is free to compare a 400w HID to 400w LED and 315cmh to 315w LED. One way or another prove there is a difference in temp rise from ambient.
@cannabineer , I know your an educator, what are your thought? Keep it simple though dude, im not the brightest button in the box.