The phenomenon of the light bulb inside a microwave oven glowing when its door is opened is known as "microwave oven cavity illumination." There are a couple of reasons why this happens:
Safety Interlock Mechanism: Microwave ovens are equipped with safety interlock switches that are designed to prevent the microwave from operating when the door is open. These switches ensure that the microwave radiation is contained inside the oven when it's in use. When you open the microwave door, one or more of these switches are activated, cutting off power to the microwave's magnetron (the component that generates microwaves). However, the control circuitry is still active, including the part that powers the light bulb. As a result, the light bulb remains on even though the magnetron is not producing microwaves.
Time Delay Circuit: To provide a brief light source when the microwave door is opened, most microwave ovens have a time delay circuit that keeps the light bulb on for a short period after the door is opened. This feature is intended to allow users to see the contents of the microwave without needing to keep the oven door open for an extended period.
It's important to note that the light bulb inside a microwave oven is not designed to indicate the presence of microwaves or any radiation hazard. Microwave ovens are designed with safety measures to prevent microwave leakage when the door is closed properly. As long as the oven is in good working condition and the door seals are intact, there should be no risk of harmful microwaves escaping when the light bulb is on with the door open.
However, it is crucial to avoid tampering with the safety interlock mechanisms or attempting to operate the microwave with the door open, as it can lead to dangerous exposure to microwaves. The light bulb's illumination is purely for convenience and visibility purposes when the oven is not in use and should not be relied upon to determine the oven's safety status.