Microwaves have dark glass windows primarily for safety reasons. The dark glass, often referred to as a microwave shielding window, is designed to prevent the escape of microwave radiation from the oven while allowing you to see inside.
Microwaves operate by generating electromagnetic waves at a specific frequency (typically 2.45 GHz) that excite water molecules and other polar molecules in the food. These excited molecules then produce heat, which cooks the food. However, these microwaves can be harmful if they escape from the oven and come into contact with living tissue, including human bodies.
The dark glass window serves as a barrier to contain the microwaves inside the oven cavity. It is constructed using a special material that is opaque to microwaves, preventing their transmission through the glass. The dark tint of the glass further reduces the amount of visible light that passes through, making it difficult to see the interior of the oven.
By keeping the microwaves contained, the shielding window helps protect people from potential microwave exposure and minimizes the risk of injury. It's important to note that even though the microwaves are contained within the oven, it is still recommended to operate the microwave with caution and avoid prolonged exposure to the emitted radiation.