Technical Glossary Refractive Index

[Refractive Index]

When light enters a material, its speed changes. The refractive index is unique to each substance and describes the difference between the speed of light within a material and the speed of light in a vacuum. It expresses the difficulty which light experiences when moving through a substance. Thus, the higher a substance’s refractive index, the slower light travels through it. The refractive index for a substance differs according to the wavelength of light used. However, it is custom to use light of wavelength 589.3 nm (the sodium D line) when evaluating.
Below is a list of the refractive indices of several common substances.

Material	Refractive Index	Notes
Air	1.000292	0℃、1 atmosphere
Carbon dioxide	1.00045
Ice	1.309	0℃
Water	1.3334	20℃
Ethanol	1.3618
Paraffin	1.48
Polymethylmethacrylate	1.491	20℃
Quartz crystal	1.5443	18℃
Optical glass	1.43-2.14
Sapphire	1.762-1.770
Diamond	2.417
Silicone rubber	1.40-1.43