This document discusses the properties of various lens materials, including refractive index, Abbe value, density, UV cutoff, and compares these properties across materials. It provides refractive index ranges for common materials from crown glass to plastics. Higher refractive index lenses are thinner but have greater density. Abbe value indicates resistance to chromatic aberration, with higher values being better. UV cutoff determines a material's ability to block harmful UV radiation, with polycarbonate and Trivex blocking more than crown glass or CR-39.

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Lens Materials and their
Properties
Vinay

2. Lens Properties
Refractive index.
Abbe Number/ Value. ( Constringence)
UV cut off.
Specific gravity.
Scratch resistance.
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3. Refractive Index (µ)
Depends upon the speed of white light inside the
material.
Hence varies according to the source of white light.
We follow the American standard light source of
Helium (d line)
Note: µ = c/ v where “ v” is the velocity of light in
lens material and “ c ” is the velocity of light in
vacuum.
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4. Higher the refractive index ; thinner will be the
lens.( lesser will be the thickness. )
Example: Index of Crown glass is 1.523
Index of CR – 39(Plastic) material is 1.4985
Index range: 1.4 to 1.9
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5. Index Classification
Normal index : 1.48 ≤ µ d< 1.54
Mid-index : 1.54 ≤ µ d < 1.64
High-index : 1.64 ≤ µ d < 1.74
Very high index : 1.74 ≤ µ d
where µ d is the µ or refractive index of the
material measured using Helium d line.
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6. Density (kg/m3
)
Density of any material is defined as the mass per unit
volume.
The higher the density, the tighter (denser) the
particles are packed inside the substance.
Density is a physical property constant at a given
temperature and density can help to identify a
substance.
Density ? Related to sp.gravity
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7. Specific gravity (unit less)
The Specific Gravity is a dimensionless unit, defined as the
ratio of density of the material to the density of pure water
at a specified temperature.
It gives an idea of the weight of one lens material on
comparison to another.
Since it is relative it lacks unit, similar to index of a
material.
Was in vogue in olden days which has been sidestepped
nowadays by density measures.
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8. e.g.: if we say CR has a specific gravity of 2.5 what it
implies is that it is 2.5 times heavier than water.
e.g.: if specific gravity of CR-39 is 2.5 and that of glass
is 5 then, glass is twice as heavy as CR -39.
Note: Specific gravity is related to Refractive Index
( µ).
Usually as index increases; specific gravity also
increases.
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9. Refractive Index Vs Density
1.9 (µ) glass : 4.0gm /cm3
1.8 glass : 3.7gm/cm3
1.74 high index plastics : 3.5 gm/cm3
1.7 glass : 3.2gm/cm3
1.6 plastics (Polycarbonate) :1.2 gm/cm3
CR-39 ( µ=1.49) : 1.32 gm/cm3
Crown glass (µ=1.523) : 2.54 gm/cm3
Trivex : 1.16gm/cm3
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10. Trivex CR- 39 Polycarbonate Mid-index
plastic
Hi-index
plastic
Refractive
Index
1.57 1.50 1.59 1.53 - 1.56 1.57 - 1.71
Abbe Value 43 58 30 32-38 32-42
Density
(g/cm3)
1.16 1.32 1.22 1.120-1.34 1.30-1.40
Scratch
Resistance
0.66 1.0 0.2 0.3-0.5 0.5
Impact
Resistance
Testing
Passes Fails Passes Fails Fails
UV Cut Off
(nm)
400 340 380 360 380
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11. Abbe Number
It is a measure of the ability of lens material to
keep white light together.( that is without
producing chromatic aberration)
 As the Abbe value increases chromatic
aberration decreases.
It is the reciprocal of the dispersive power of
the materials.
It is inversely proportional to refractive
index.
e.g.: Abbe Value of Poly carbonate 30 and CR-39--58.07/16/19 11

12. Increasing order
Density:
Trivex < Polycarbonate < CR-39 < Crown glass.
Abbe number:
Poly carbonate < Trivex < Crown glass < CR -39
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13. ULTRA VIOLET (UV) RADIATION (UVR)
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UV CLASSIFICATION
ABBRE-
VIATION
RANGE NOTES
Near NUV 400 nm - 200 nm ENTERS EARTH
Long wave or black
light
UVA 400 nm - 320 nm
CAUSES OCULAR
DAMAGE
Medium wave UVB 320 nm - 280 nm
BLOCKED BY USUAL
LENS MATERIAL
Short wave or
germicidal
UVC Below 280 nm
BLOCKED BY USUAL
LENS MATERIAL
Far or vacuum FUV, VUV 200 nm - 10 nm BLOCKED BY OZONE
Extreme or deep EUV, XUV 31 nm - 1 nm BLOCKED BY OZONE

14. ULTRA VIOLET (UV) RADIATION (UVR)
Natural sources of UV
Sun emits UV-A , UV-B, and UV-C
Atmosphere's absorbs almost whole of UV- C and UV-
B through ozone layer.
Thus only UVA reaches the Earth's surface.
.
Ordinary crown glass is partially transparent to UVA
but is opaque to shorter wavelengths.( uv b and c)
While quartz or Silica glass, depending on quality, can
be transparent even to vacuum UV(FAR
UV)wavelengths.
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15. Since radiation in UV-A range (320-400nm)
causes ocular damage, it is important for a lens
material to cut off this range of wave length.
The lens material can be arranged in the
following (increasing) order based on their
effectivety in absorbing UV-A.
Crown glass < CR-39 < Polycarbonate or Trivex
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Lens Materials

17. Lens material
Crown glass
Plastic CR-39
Trivex™
Polycarbonate
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18. Crown glass
Refractive index (nd): 1.52288
Abbe value(Vd): 58.5
Density: 2.55 g/cm³ (the heaviest corrective lens
material in common use, today)
UV cutoff: 320 nm
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19. CR 39
Refractive index (nd): 1.498 (standard)
Abbe value(Vd): 59.3
Density: 1.31 g/cm³
UV cutoff: 355 nm
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20. Trivex™
Refractive index (nd): 1.532
Abbe value(Vd): 43 - 45
Density: 1.1 g/cm³ (the lightest corrective lens
material in common use)
UV cutoff: 380 nm
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21. Polycarbonate
Refractive index (nd): 1.586
Abbe value(Vd): 30
Density: 1.2 g/cm³
UV cutoff: 385 nm
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