2 A B C D E F G H I K L M N O P R S T U V W
Ra Re

refractive index

refractive index = \frac{speed\ of\ light\ in\ vacuum}{speed\ of\ light\ in\ the\ current\ medium\ (eg.\ glass)}

In other media than vacuum the light is slower. Therefore, the smallest refraction index is 1.
Glass slows down light of different wavelengths (“colors”) by different factors.
Result is different refractive indices, “depending on the light color.”
The higher the refraction index, the stronger the change of direction at the boundary between different media
As media have different refraction index for blue, green red light, red/green/blue light takes a different path through a lens!
Medium typical refractive index
Vacuum 1
Air 1.000293
Helium 1.000036
Hydrogen 1.000132
Carbon dioxide 1.00045
Water at 20 °C 1.333
Ethanol at 20 °C 1.36
Olive oil at 20 °C 1.47
Ice 1.31
PMMA (= acrylic = plexiglas) 1.49
Window glass 1.52
Polycarbonate (Lexan™) 1.58
Flint glass (typical) 1.62
Sapphire 1.77
Cubic zirconia 2.15
Diamond 2.42
Moissanite 2.65

Related entries