Typical Values
| Material | n |
|---|---|
| Gases at 0 °C and 1 atm | |
| Air | 1.000293 |
| Helium | 1.000036 |
| Hydrogen | 1.000132 |
| Carbon dioxide | 1.00045 |
| Liquids at 20 °C | |
| Water | 1.333 |
| Ethanol | 1.36 |
| Benzene | 1.501 |
| Solids | |
| Ice | 1.309 |
| Fused silica | 1.46 |
| PMMA | 1.49 |
| Crown glass (typical) | 1.52 |
| Flint glass (typical) | 1.62 |
| Diamond | 2.42 |
For visible light most transparent media have refractive indices between 1 and 2. A few examples are given in the table to the right. These values are measured at the yellow doublet sodium D-line, with a wavelength of 589 nanometers, as is conventionally done. Gases at atmospheric pressure have refractive indices close to 1 because of their low density. Most plastics have refractive indices in the range from 1.3 to 1.7, but some high-refractive-index polymers can have a value as high as 1.76.
For infrared light refractive indices can be considerably higher. Germanium is transparent in this region and has a refractive index of about 4, making it an important material for infrared optics.
Read more about this topic: Refractive Index
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