The ratio of the speed of light in a vacuum or in air,
c, to the speed of light in a given medium,
v.
Symbol:
n. Hence,
n = c/v
The speed of light in a given medium depends upon its wavelength. Consequently, the index of refraction varies accordingly, being greater for short wavelengths (blue) than for longer wavelengths (red). The index of refraction forms the basis of Snell's law, which quantitatively determines the deviation of light rays traversing a surface separating two media of different refractive indices.
Syn. refractive index.
Plural: indices.
See dispersion;
law of refraction;
gradient-index lens;
high index lens;
speed of light;
refractometer.
| Table I3 Refractive indices of some transparent media at selected wavelengths |
| spectral line | | G | | F | | D | | C | | A |
| Origin | | Calcium | | Hydrogen | | Sodium | | Hydrogen | | Oxygen |
| wavelength (nm) | | 430.8 | | 486.1 | | 589.3 | | 656.3 | | 759.4 |
| aqueous or vitreous humour | | 1.3440 | | 1.3404 | | 1.3360 | | 1.3341 | | 1.3317 |
| crystalline lens | | 1.4307 | | 1.4259 | | 1.4200 | | 1.4175 | | 1.4144 |
| spectacle crown | | 1.5348 | | 1.5293 | | 1.5230 | | 1.5204 | | 1.5163 |
| dense flint | | 1.6397 | | 1.6290 | | 1.6170 | | 1.6122 | | 1.6062 |
| Table I4 Index of refraction n of various media for sodium light (λ = 589.3) |
| air | 1.00 |
| water (at 20ºC) | 1.333 |
| spectacle crown glass | 1.523 |
| flint glass (dense) | 1.62 |
| flint glass (extra dense) | 1.65-1.70 |
| titanium oxide glass | 1.701 |
| calcite crystal | |
| ordinary ray | 1.658 |
| extraordinary ray | 1.486 |
| quartz crystal | |
| ordinary ray | 1.544 |
| extraordinary ray | 1.553 |
| |
| diamond | 2.42 |
| Canada balsam | 1.53-1.54 |
| CR-39 | 1.498 |
| polycarbonate | 1.586 |
| silicone rubber | 1.44 |
| CAB | 1.47 |
| PMMA | 1.49 |
| HEMA | 1.43 |
| hydrogel polymer | |
| 20% water content | 1.46-1.48 |
| 75% water content | 1.37-1.38 |
| eye | |
| tears | 1.336 |
| cornea | 1.376 |
| aqueous humour | 1.336 |
| crystalline lens (average effect) | 1.42 |
| vitreous humour | 1.336 |