Occasionally, when using power settings that are lower then the normal 100% cooking power, the light inside the microwave cavity may dim. This is normal, though may not happen every time, and has to do with how the microwave lessens the cooking power for things like reheating and defrosting. If concerned, reset the cycle and put 1 cup of water in a microwave safe container and place it in the microwave. Cook for 1 minute. The light will be on full power during this cooking cycle.