Index of Refraction Calculator

The Slowing of Light

The index of refraction ($n$) of a material is a dimensionless number that describes how fast light travels through that medium relative to its speed in a vacuum. It is one of the most fundamental properties in optics.

When light enters a medium like water or glass, it interacts with the atoms and is constantly absorbed and re-emitted. This process creates a delay, making the effective speed of the light slower than the universal constant $c$.

Typical Refractive Indices

• Vacuum: exactly $1.0$.
• Air: $\approx 1.0003$ (almost the same as vacuum).
• Water: $\approx 1.33$.
• Glass: $\approx 1.5$ (depending on the type).
• Diamond: $\approx 2.42$ (one of the highest known, causing its extreme sparkle).

The Formula

Example Calculation

Light travels through a specific type of plastic at $200,000,000 , \text{m/s}$.

1. Constant c: $\approx 300,000,000 , \text{m/s}$.
2. Divide: $300,000,000 / 200,000,000 = 1.5$.

The index of refraction for this plastic is $1.5$.