Refractive Index

Refractive Index

The speed of light in a vacuum divided by the speed of light in matter, which is a measure of how light travels in matter.
Light (wavelength) travels smoothly in a vacuum (air for practical purposes), but in matter it slows down because of resistance. Instead, it tries to take a shortcut by changing the direction it travels (refraction) to get through faster.
The higher the value of the refractive index of a substance, the greater the refraction of light relative to the angle of incidence.

The higher the refractive index of a substance, the greater the difference in refractive index between it and air, and the greater the reflectance.
As the reflective index increases, the transmittance decreases. Diamonds have a refractive index of 2.42, which is very high, and they reflect light easily, making them sparkle.
Transmittance is important for optics-related materials, and by adjusting the refractive index and coating thickness, the transmittance can be increased.