When light wave suffers reflection at the interface from air to glass, what is the change in the phase of reflected wave?

When light is reflected off a more dense medium with higher index of refraction, crests get reflected as troughs and troughs get reflected as crests. The wave is said undergo a 180⁰ change of phase on reflection. The net effect of the phase change is that the reflected ray ``jumps ahead" by half a wave length.