Yesterday I visited the Exploratorium, and hung out in front of their giant concave mirror, where things get larger instead of smaller as you walk further from the mirror surface.
What I didn't see before, though, was they have a smaller, similar mirror in front of a heater, and when you wave your hand in front of you, it becomes warmer when it obscures the image of the heater from your point of view.
In hindsight, it's a mundane phenomenon. Heat is light. But what a great demonstration!