index of refraction

Index of refraction

A constant number for any material for any given color of light that is an indicator of the degree of the bending of the light caused by that material.

Mentioned in: Eye Glasses and Contact Lenses

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index of refraction

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