\[R=\left(\frac{n_1-n_2}{n_1+n_2}\right)^2\]
Variables
Rreflectance
n1refractive index of the incident medium
n2refractive index of the transmitted medium
Description
What is this formula?
The Fresnel reflectance formula at normal incidence calculates the fraction of light intensity reflected at the boundary between two optical media when light strikes perpendicular to the surface.
When to use it
Use this formula when analyzing optical interfaces, coatings, lenses, fiber optics, windows, and transparent materials where light incidence is normal to the surface.
Example
Light passes from air into glass.
Data:
n1 = 1.00
n2 = 1.50
Formula:
R = ((n1 - n2)/(n1 + n2))²
Substitution:
R = ((1.00 - 1.50)/(1.00 + 1.50))²
Result:
R = 0.04
Approximately 4% of the incident light is reflected at the interface.
Applications
Optical coatings, anti-reflective surfaces, laser systems, fiber optics, lens design, optical sensors, and photonics engineering.