polycarbonate (redirected from Makrolon)

Polycarbonate

A very strong type of plastic often used in safety glasses, sport glasses, and children's eyeglasses. Polycarbonate lenses have approximately 50 times the impact resistance of glass lenses.

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

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plastic 

Various organic or synthetic materials (e.g. CR-39, HEMA, polymethyl methacrylate, polycarbonate, etc.) that can be transformed into solid shapes to make spectacle frames, contact lenses, ophthalmic lenses, etc. and can be made to have good optical surfaces, high light transmission and refractive indices and dispersions similar to that of crown or flint glass. See acetone; index of refraction; plastic spectacle frame.