• Total internal reflection (TIR) occurs when:

The angle of incidence is greater than the critical angle and the incident refractive index?n1?is greater than the refractive index of the material at the boundary?n2

• Therefore, the?two?conditions for total internal reflection are:
  • The angle of incidence,?θ1?> the critical angle,?C
  • Refractive index?n1?> refractive index?n2?(air)

Diagram showing refraction, the critical angle and total internal reflection

• Two conditions are necessary for total internal reflection to occur:
  • The light must be going from a?more dense medium?into a?less dense?one
  • The?angle of incidence?must be?greater?than the?critical angle