Microwave Light Dims During Operation

The intensity of the microwave's cavity light varies during operation of the microwave. This will occur during normal usage if the power level is set below high (or below 10) because of the cycling of the magnetron tube.

 

For example, Defrost and Reheat operate at various power levels to improve cooking performance.  For these cycles the magnetron will cycle on and off.  When the magnetron turns on it causes a brief voltage drop (line sag) on the incoming powerline to the receptacle that causes the oven lights to dim briefly and in some cases, the turntable to slow.  This is normal operation.