What does the mirror reflection effect in the hall mean?

It means that if the reflective surface is relatively smooth, when the parallel incident light hits the reflective surface, it will still be reflected parallel in one direction. This reflection is a specular reflection.

Specular reflection refers to the reflection of reflected waves (electromagnetic waves, or sound waves, water waves) with a certain direction; the direction of the reflected wave is at an angle (reflection angle) with the normal line of the reflection plane, and is with the direction of the incident wave. The angles between the normals of the reflection plane (angle of incidence) are equal, and the incident wave, reflected wave, and plane normal are in the same plane.

When taking photos, you should avoid specular reflection light entering the camera lens. Because the specular reflection light is extremely strong, it will form a white bright spot on the photo, which will affect the appearance of the ground objects themselves in the photo.

Principle of mirror reflection

When light travels to the interface between two media, part of it returns to the original medium. If the unevenness of the interface at the incident point is much smaller, it can be regarded as a smooth interface. If there is both radiation and diffuse reflection, it is called mixed reflection. During diffuse reflection, if the brightness of light in different directions is the same, it is called uniform diffuse reflection.

During the same reflection process, some wavelengths of light are reflected more, which is called selective reflection. Coating technology can be used to change the optical properties of the media interface to reduce or increase the light component of a certain wavelength in the reflected light to adapt to the requirements of different optical components.