way less heat, almost zero. This was the main appeal for me, that and the decreased power consumption. You can't put the plants super close to the light though, even though they don't produce much heat, the intensity of the diodes will bleach the pigment out of your plants. You'll notice on my last pics that I had them a bit too close for about a week on this run and leached a bit of the color off the tops. Doesn't really affect taste or quality as long as it isn't severe bleaching. It kind of looks like a N def, but upon closer inspection it isn't, the lower branches maintained their full color and health. It's a totally different game than hid or cfl, but one that has a quick learning curve. I'm getting the hang of when to move the lights up.
The difference in temps compared to my old set up was pretty dramatic. My spare bedroom closet used to get close to 100F if not more, now its running in the low 70s, same as the rest of my house. Gotta keep leds with 3w diodes at least 7-8 inches away in flower, 10 in veg. The 2w diode 90w ufo and 1w diode 90w ufo can be put much closer to the plants (4-5 inches).