What is the term for the area where light enters?

The term for the area where light enters is the pupil. The pupil is an opening located in the center of the iris in the eye, and it regulates the amount of light that can enter. Its size adjusts automatically, becoming larger in dim light to let in more light, and smaller in bright light to protect the retina from excessive brightness. This mechanism is crucial for maintaining optimal vision in varying lighting conditions.

Other terms like umbra and penumbra are related to shadows and light projections, typically used in contexts such as eclipses, where they describe regions of partial and total shadow. A reflector, on the other hand, refers to an object that redirects light, rather than being an area where light enters. Understanding these distinctions clarifies why the pupil is the correct term in this context.