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Bill Beaty at Science Hobbyist - Unwise Microwave Oven Experiments: after a disclaimer warning you not to try this at home... ["metjohn"]
Years ago I was living with roommates, and while working in the kitchen I noticed that the fluorescent light over the sink was about 8 inches long. A light went on in my brain ;) because I'd always wondered what would happen if a fluorescent tube was placed in a microwave oven. In theory the RF energy should have enough voltage to ignite the mercury vapor into a plasma, and the lamp should light. But standard ovens put out at least 500 watts, so the tiny fluorescent tube should light quite brightly, to say the least. I'd never before encountered a fluorescent tube which was short enough to fit in an oven. So, I pulled out the tube, stuck it in the oven, said "THEY'RE HEEEEEERE!" , and punched the ON switch. Sure enough, the kitchen was lit up by a blue-white blaze of light coming from the front of the microwave oven. I only let it run for about 1 second, but this was enough to heat the fluorescent tube so it was too hot to touch.