index of refraction

In optics, a property of mediums through which light passes, the ratio of the velocity of light in a vacuum (c) to its velocity in the medium. It varies with the wavelength of the light. The symbol is n.

The index of refraction can also be expressed in terms of the permeability and dielectric constant of the medium:

$An equation. n equals the fraction c over v, or equals the square root of the fraction whose numerator is mu times epsilon and whose denominator is mu sub oh time epsilon sub oh$ ,

where μ₀ and ε₀ represent the permeability and dielectric constant, respectively, of the vacuum.

Some Examples
Material	Index of refraction at 546.1 nanometers
dry air at 15°C, 1 atm pressure	1.000 277 82
carbon dioxide, STP	1.000 410
water at 30°C (589 nm)	1.332 30
fused silica	1.460 08
Plexiglas	about 1.49
crown glass	1.513 14
borosilicate crown glass	1.518 72
crown flint glass	1.519 78
phosphate crown glass	1.527 36
polystyrene at 20°C (589 nm)	1.591
flint glass	1.607 18
dense crown glass	1.609 94

Schott Optical Glass.
Schott Glass Technologies, Inc.

B. Edlin.
Metrologia, vol. 2, page 71 (1966).

P. Schiebnener, J. Straub, J. M. H. Levelt Sangers and J. S. Gallagher.
J. Phys. Chem. Ref. Data, vol 19, pages 677 and 1617 (1990).