Lesson 3 – Reflection + Refraction

When optical radiation (UV, Vis, or IR) interacts with material surfaces that are smooth and shiny, it can either reflect from the surface of the material or transmit through it. Reflection is straightforward: the angle a light ray intersects a material surface with respect to the surface normal (a perpendicular line to the surface) equals the angle it reflects from the material (with respect to the same surface normal). Transmission is more complicated in that the material’s ability to slow light comes into play; this material property is called its refractive index. The angle to which light moves when traveling into a material (with respect to the surface normal) is determined by an equation called Snell’s Law. This depends on the light’s initial angle (angle of incidence) with respect to the surface normal, the refractive index of the incident material, and the refractive index of the next material.