Microwave ovens produce electromagnetic (EM) radiation at about 2450 MHz.  In the spectrum of radio transmission frequencies, this is a very high frequency.  But compared to light frequencies, it's very small.

Green light is in the middle of visible EM radiation.  The frequency of green light is about 24,000 times greater than microwave oven radiation.

Microwaves heat food by vibrating molecules in the food.  But microwave EM radiation can also induce electrical currents in conductors.  If a non-conductor gets hot enough, or if enough voltage is applied, ionization can cause it to become a conductor.  To demonstrate these effects, we put various conductive materials in a microwave oven under controlled conditions.

The materials used in these experiments were relatively non-toxic, and the duration of each experiment was typically 15 seconds or less.

DO NOT RANDOMLY PUT MATERIALS IN A MICROWAVE OVEN.  Experiment only after you've done research and know what you are doing.  Safety first!  Do not defeat the safety mechanisms of a microwave oven.  Minors should have permission and adult supervision. 

I do not recommend putting in lamps that contain mercury.  ALL fluorescent lamps contain mercury.  If the lamp erupts, you will have a poisoned microwave oven, and the oven fan will blow mercury vapors into the room.