The experiment of total internal reflection phenomena Shine a light beam from glass to the air. To increase the incident angle, observe the brightness of incident rays and reflected rays, refracted rays. Increasing the incident angle until refracted angle equals to pi/2. At this point, the incident angle equals to limiting angle,called critical angle. When the incident angle is greater than critical angle, complete reflection of a ray of light within glass from the surrounding surfaces back into the medium. There is no refracted refracted ray of light in the second medium (air). because it is impossible to have the case r>pi/2 This phenomena is called the total internal reflection phenomena.