According to some old data I posted back in july 2013, when I was installing it, the temperature of the LED test point is 110 degrees with no chimney, and 80 degrees after the chimney was added.
Right now, I did a similar test with thermal imager.
Without a chimney, within 30 minutes the temperature of heatsink reaches 121°C. With the chimney on, the temperature after 30 minutes is 94 °C. Still getting this near-30°C-drop, but substantially higher absolute values (it seems there was something wrong with thermocouple-soldering way I did it previously. Or is it just dust?)
The drop may not sound like being much, but it can make a hell of a difference for LED lifetime.
If you are wondering, wtf is on the right side of the photo. It is.. no.. it was a halogen lamp that I used before this LED light. Until it blew up like a bomb, throwing red-hot pieces of quartz all over the place. Guys, don't use halogen lamps without shields. No, really.