Physics > Refractive Indices
The refractive index of a medium (material) is a measure for how much the speed of light (or other waves) is reduced inside the medium. Standard glass has a refractive index of 1.5, which means that light travels at 1 / 1.5 = 0.67 times the speed in air or vacuum. Two common properties of glass and other transparent materials are directly related to their refractive index. First, light rays change direction when they cross the interface from air to the material, an effect that is used in lenses. Second, light reflects partially from surfaces that have a refractive index different from that of their surroundings.
The table below shows the refractive indices of common materials:
| Material |
Refractive Index (n) |
| Vacuum |
1.00000 (exactly) |
| Air (STP) |
1.00029 |
| Acetone |
1.36 |
| Alcohol |
1.329 |
| Chromium Oxide |
2.705 |
| Copper Oxide |
2.705 |
| Crown Glass |
1.52 |
| Crystal |
2.00 |
| Diamond |
2.417 |
| Emerald |
1.57 |
| Ethyl Alcohol |
1.36 |
| Fused Quartz |
1.46 |
| Heaviest Flint Glass |
1.89 |
| Heavy Flint Glass |
1.65 |
| Glass |
1.5 |
| Ice |
1.309 |
| Iodine Crystal |
3.34 |
| Liquid Carbon Dioxide |
1.20 |
| Polystyrene |
1.55 |
| Quartz |
1.644 |
| Ruby |
1.77 |
| Sapphire |
1.77 |
| Sodium Chloride (Salt) |
1.544 |
| Sugar Solution (30%) |
1.38 |
| Sugar Solution (80%) |
1.49 |
| Topaz |
1.61 |
| Water (20°C) |
1.333 |
| Zinc Crown Glass |
1.517 |