Change of phase due to reflection Lloyd's mirror(洛埃镜) An electromagnetic wave undergoes a phase change ofπ upon reflection from a medium that has a higher index of refraction than the one in which the wave is traveling Change of phase due to reflection Lloyd’s mirror（洛埃镜）: An electromagnetic wave undergoes a phase change of  upon reflection from a medium that has a higher index of refraction than the one in which the wave is traveling