There is very little heat from a hps that isnt ir in reality, seriously very inefficient thermal/convection/conduction heaters and you will need more wattage to heat a room which is where traditional heaters do not use light so much as thermal mass and higher wattage.
Hps are not air heaters, mainly the heat is ir and still far from what the sun kicks out, dont believe me then go stand in a field in Afghanistan in mid summer and tell me them plants are suffering.
The point on air flow is correct, vpd is pretty useless, leaf cooling is by far a more complex subject and deals with how a leaf transpires even in stagnant air through thermal upflows.
Im not here to argue but i can take a stance and say all is not as it seems and a lot of led science is easily dismissed, before leds peeps didnt struggle so much in hotter countries but since led some whole new brand of science has sprung up and it dosent correlate with what universities teach (michigan)......
It's a difference between the heat the sun provides, natural air flow or other mechanisms us less than amateurs understand compared to indoor. What I do know for certain is that the ''pro'' growers you mention don't actually put the lights close from what I've seen. They hang lots of 1k lights high, more than you'd typically use to cover the same % area in an amateur indoor grow. The reason being from what I understand is that it removes the immediate physical heat generated from the bulbs but at a cost of light saturation, thus the reason they use more lights to get that back. This gives them cooler canopy temps in the physical sense and no heat stressed fluffy top buds across the canopy. Indoor growers don't have the cash or likely ventilation to do the same as pro setups so they use less lights and run them closer. The result is good yield yes, but very varied quality across the canopy, such as heat stressed fluff bud near hot zones.
The sun isn't a focused beam but putting a light in a closed hood and having it close to a plant most certainly is.. so while the sun is way more powerful it does not focus any of that light on a cm2 area of a leaf, indoor lights and reflectors can and do that. I don't need to prove it, we've all seen it.
If you hold a marginally concave translucent object over an outdoor plant it will begin to focus light and fry the area, I had an inquisitive enough child hood to have done that personally, only on ants o0. Car windows are doing the same, it's effects have been researched on magnifying the sun in a harmful way for us. Outdoor gardeners also suggest not to water plants on a hot day because the droplets will magnify and burn the leaves.
I'm not being argumentative it's just that your logic of ''the sun is hot plants don't burn'' is flawed in how you are trying to apply it to justify hps. I thought you had found a way to maintain a closer hps distance whilst avoiding the downsides, so I was very curious.
Vert gorwers use a floor fan, that will likely keep the leaves moving more to remove some of the single spot magnification issues. The fan is also constantly blowing on the bulb/s pushing hot air directly up and off the canopy. Fans on horizontal mainly push the heat into the canopy in actual practice. They also don't use hoods, another big factor.
