This is the most perfectly timed thread I've found so far, thank you so much for this info.

I'm not in the Desert, quite the opposite in fact as I am in the Northern UK and we rarely even see the sun! lol
But I do have heat issues whenever I switch on my second 600W HPS in the flower room as the temps climb from the low 80s with 1 light, to the high 90s when both are on.
This has lead me to limit myself by only using half of the room which really isn't enough for what I need.

I have a powerful exhaust fan with a carbon filter and plenty of circulation but I've been scratching my head to figure out what I can do to reduce the temp with both lights.

I was contemplating putting in an intake fan but there are too many difficulties involved with bringing the air in by stealth and this was worrying me.
But you seem to not rate the value with them anyway?

My main question here though, is that I usually grow hydroponically and will be doing so when using both lights in the future.
Why would it be any different for hydro than for soil as you stated in your opening sentence?
Is it to do with the root systems not having the protection of the soil or do the plants in general behave differently between the 2, maybe more sturdy when in soil?

Cheers!