Don't you hate it when you heat something in the microwave, and it comes out with some sections fried to a crisp, while others remain ice cold. Most people learn where to put things on the turntable in their oven to ensure even cooking, but this guy set up an experiment that actually shows you the distribution of the microwaves using lights.
He took a clear acrylic sheet, and embedded a bunch of tiny neon bulbs in a grid pattern. As the microwaves try to cook the sheet, the energy causes the bulbs to light at the point where they are struck. It's quite a light show!