Total Internal Reflection
The complete reflection of a light ray inside an optically denser medium when striking the boundary with a rarer medium at an angle exceeding the critical angle.
Governing formula
sin θ_c = n2 / n1 (where n1 > n2)
SI unit
Degrees (°)
In depth
When light travels from dense ($n_1$) to rare ($n_2$) medium at incidence angle $θ_1 > θ_c$, no refraction occurs and 100% of light energy is reflected internally back into $n_1$.
Examples in the real world
Guiding data signals across thousands of kilometers inside silica optical fibers, or sparkling brilliance in cut diamonds.