@churchhaze I think the context of this entire discussion is wrong.
You have resistive heating, whereby at most you can have 100% efficient heating.
Then you have light. Light is not heat.
When looking at efficiency of different light fixtures you're looking at (ideally) their ability to convert electricity into light. If the fixture is 60% efficient then you get 60% light and 40% resistive heat.
However, I can take a 600 W 100% efficient light and put it in an ideally insulated chamber. I can take a 600 W resistive heater and put it in an ideally insulated chamber. I can take a 600 W 60% efficienct light and put it in an ideally insulated chamber. They will all heat up the chamber the same amount.
Why? Light is energy, energy can not be created or destroyed. The light hits the surface of the insulation, the energy is absorbed and dissipated back out as heat.
So why aren't we growing plants with resistive heaters?
Plants are able to absorb light, not heat, albeit to a point - 85 degrees F at 1200 ppm CO2 up to 2000 umol/s can be absorbed by cannabis, so heat does play a factor. They can't absorb as much light at lower temperatures.
This light is absorbed by the plant and the energy is used to help the plant grow - it is not turned back into heat until you smoke it or it composts.
The ideal light would be 100% efficient and it would be able to deliver 2000 umol/s to a plant that was capable of utilizing all of this light. There would be no heat generated from this system. This would never happen - the light dissipates heat as it travels through the air even due to the same aforementioned principles it did with the insulation. However, if it did - you would then need to use some sort of heater to keep temps at 85 degrees.
Today's lights are no where near this efficiency - in order to deliver the amount of light the plants require they are producing well over the necessary amount of heat for optimal growth.
Perhaps in the future someone can genetically engineer a virus that will insert the DNA of a bacterium from well below the earth's surface which does use heat to grow and insert it into plants - global.warming.solved.