During the day, the train window shows the outside landscape, which is hardly obscured by the reflections in the glass. After dusk, the inside of the train carriage begins to appear in the window. Eventually, the landscape behind the window disappears completely. When it is dark outside, the surface of the glass reflects a mirror image of the inside of the carriage. However, the window glass works at night just as it does during the day. The only difference between day and night is that during the day, the light coming from outside is so bright that it obscures the reflections of the glass. The more obliquely the surface of a window is viewed, the greater its reflectivity. On the train, you can observe your fellow passengers more clearly from a window farther away than from a window right next to you.

When light hits a window, some of the light passes through the window or refracts, whereas some of the light is reflected back towards its source. If the glass is flat, the following laws apply to the reflected beam:

(1) The reflected radius is in the same plane as the incident radius and the perpendicular of the surface.
(2) The angle of incidence is equal to the angle of reflection.

If the surface of the glass is uneven, a reflection will occur in all directions, making it impossible to see through the window. Visible light is best reflected by metals such as aluminum and silver, which reflect more than 90% of the light that arrives at their surface. That is why these materials are used in mirrors.