The right-angle prism can be used as a 90° reflector due to total internal reflection (TIR). When light is incident from one right-angled face of the prism, the light will be totally internally reflected at the glass/air interface of the inclined plane and exit from the other right-angled face. . Right-angle prisms can deflect incident light by 90°, so they are a good replacement for reflectors. A right-angle prism can also be used as a 180° retroreflector, as shown in Video 2 below right. When the input light is incident from the oblique face of the prism, the light will undergo total internal internal reflection at the glass/air interface of the rectangular face. The second total internal reflection occurs when passing through the next right-angled surface, and finally emerges from the inclined surface in a direction parallel to the incident beam. Like a retroreflector, the 180° deflection of the light path is independent of the angle of incidence.