Setup: A light bulb is placed in a glass of water and both are placed in a microwave oven. The bulb "lights up" when the power is turned on.

Observations:  

• The water is necessary so that the microwaves will not interact with the metal screw-end part of the light bulb. The frequency of the microwaves (of commercial microwave ovens) are tuned to the same frequency as that of one of the one of the rotational mode frequencies of water. This resonance causes the microwaves to be absorbed by the water.
• The water has no other effect except as a heat sink. The bulb will still grow even when the helical filaments are broken off. In this case there can be no normal flow of current. Putting salt in the water will not make the bulb glow brighter.
• The glow is caused by eddy current heating of the metal parts of the filament. In particular the small loops that hold the helical filament ends glow the brightest. A large AC current is generated in the loops which heats the loops through P = I² R.
• The changing brightness is caused by the rotation of the filament in and out of "hot spots" of microwave intensity concentrations.
• After a while a bulb will stop glowing.
• What causes the auroral grow is unknown by me.