They look deadly. It would be interesting to see how much they sell for.looking at these at the moment....
http://www.lowcarbon-led.com/product/led-high-bay-light-300w.html
http://www.mouser.com/Cree-Inc/Optoelectronics/LED-Lighting/LED-Emitters/High-Power-LEDs-White/_/N-8usfj?P=1yzs6io&Ns=Pricing|1are they on sale yet ?
It's not out of control, and most of it goes to the heat sink so it isn't beamed into your plant canopy. The driver puts off a good amount of heat, though, so plan on keeping that somewhat remote if you're worried about it. It's sort of relative, it depends on how big the grow space is and what ambient temps already are. You could also make a box to place all your drivers inside and then just vent that outside, or something.how much heat is released from these high watt led's ?