Huygens' principle of secondary wavelets can be applied to

Huygens' principle states that every point on a given wavefront acts as a fresh source of secondary wavelets. The forward envelope of these secondary wavelets at any instant gives the new position of the wavefront.

This principle is used to trace the propagation of light waves and can successfully derive the laws of reflection and refraction, including Snell's law.

Since it is based on the wave theory of light, it cannot explain the particle nature of light. It also does not provide a method to calculate the velocity of light in vacuum.