Laws of Reflection and Refraction via Huygens's Principle
This Demonstration shows the reflection and the refraction of a light beam and the formation of the wavefronts of the reflected and/or refracted beams. According to Huygens's principle, each point of the incident beam at the interface can be considered a point source of light, emitting spherical waves. The envelopes of these elementary waves then combine to produce the reflected and refracted waves.
 Wikipedia. "Huygens–Fresnel Principle." (Jan 9, 2015). en.wikipedia.org/wiki/Huygens% E2 %80 %93 Fresnel_principle.
"Laws of Reflection and Refraction via Huygens's Principle"
Wolfram Demonstrations Project
Published: January 13 2015