polycarbonate(redirected from Polycarbonates)
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polycarbonate(pŏl″ē-kăr′bĭ-nāt, -nĭt) [″ + ″]
A transparent polymer used to manufacture eye protectors, shields, and other medical devices.
Medical Dictionary, © 2009 Farlex and Partners
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
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
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/vThe 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|
|aqueous or vitreous humour||1.3440||1.3404||1.3360||1.3341||1.3317|
|Table I4 Index of refraction n of various media for sodium light (λ = 589.3)|
|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|
|20% water content||1.46-1.48|
|75% water content||1.37-1.38|
|crystalline lens (average effect)||1.42|
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.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann