Microwaves are absorbed by wires creating current in the wires which can drive a neon lamp. Marc "Zeke" Kossover high school science teacher drilled a grid into a piece of plastic and slipped in the bulbs, leaving the wires to hang out like antennas. As the plate turns, the bulbs go into and out of places where the microwave energy is denser, illuminating the bulbs. No, it doesn't seem to hurt the microwave.
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