You seem to have misunderstood, heat from a HPS is not a challenge but both an advantage and a necessity to grow in the dutch climate most of the year (4 out 5 cycles). It allows me to keep my full spectrum HPS at an ideal distance providing more than enough light on a maximum surface while achieving an optimal temp as a bonus, without any form of additional heating required. We rarely use cool tubes. With LED it requires additional heating most of the year which is expensive and requires additional space (a rare commodity sort of speak). 75% of the police detectives and 50% of the entire force here are working are focused on raiding grows, in other words stealth is a major factor here. One of the things that gives growers away is the use of electricity and scanning (even from choppers and drones) for what they refer to as heat lamps (HPS bulbs shows up very clearly in attics etc). If LED were a viable technology in NL to grow top quality+quantity mj we'd be all over it. If I were in Spain I'd surely give it a try, but again in the Netherlands LED just isn't relevant for commercial quantity growers/coffeeshop suppliers (google images search for 'hennepkwekerij' to see what pro grows look like here).
And no, that 50% is simply not true. Clearly you guys haven't measured it and there's some wishful-thinking involved. The facts are quite easy to find. Here's an example from a more reliable source:
http://www.lighting.philips.com/main/application_areas/horticultural/ See "Efficiency of LED toplighting system vs HPS systems" and that's in a greenhouse, in a closet or tent or room with as I mentioned earlier a quality reflector hood and proper reflection the efficiency of HPS is over 80%.
If LED were half as good as some people claim LED sellers wouldn't have to make up such bogus claims. If LED were as good as some people claim we would have solved a lot of energy, food and economic problems.
Dutch grow closets/rooms/tents are all very similar based on a tried and proven design where efficiency (gpw on a given limited space) means everything. A HPS is key to that design and you can't replace just that item without completely redesigning the rest of the setup, in particular in terms of heating. Cold and humidity (not just from transpiration) is the real challenge here, heat is only a challenge 3 months a year and that's stretching it.
From that same link, advantages of LED:
"Less heat radiation
LED lighting produces significantly less heat than
conventional HPS lamps, so you can control your
greenhouse climate more accurately.
The convection
heat that is still being produced can often help to save
on your gas* bill. Less heat also means you can use light
more effectively, for example by increasing light level
extending lighting periods, or by using light on warmer
days without having to ventilate. Less heat also means
you can place the light source closer to your plants,
reducing light loss – so close in fact that you can now
use toplighting even in low-ceiling greenhouses."
*I pay roughly 4 times as much on gas as on electricity (total for home). See my point?
As I wrote in my other post:
It would require the opposite of a cooltube sort of, e.g. somehow use the heat from the LED device to warm up the air that is sucked in through the intake at the bottom of the grow closet/tent. Which obviously isn't going to work well. That bold part isn't going to work in a typical setup unless I would turn off the exhaust, killing another essential item in the interconnected setup leading to far less CO2, more humidity and less temp control (I control the temp with a thermostat on my exhaust...).