One of the founders of Burning Man uses a parabolic reflector to light the cauldron that resides in Center Camp for the duration of the event. It's happy-making to consider where she must have gotten the idea. (And I should really try to make it to the official lighting this year. I've fed the cauldron - they keep a pile of firewood nearby, and everyone is invited to add a piece as they pass during the week - but I've never seen it be lit.)