Editing Specular reflection (section)

=== Internal reflection ===
When light is propagating in a material and strikes an interface with a material of lower [[index of refraction]], some of the light is reflected. If the angle of incidence is greater than the [[critical angle (optics)|critical angle]], [[total internal reflection]] occurs: all of the light is reflected. The critical angle can be shown to be given by
: <math>\theta_\text{crit} = \arcsin\!\left(\frac{n_2}{n_1}\right)\!.</math>