MATERIAL

GLASS

PLASTIC

POLYCARBONATE

Method

Chemically or Heat toughened

   
Hardness

Excellent

Fair

Fair

Chemical Resistance

Excellent

Fair

Good

Resistance to hot particles

Poor
(hot metal fuses with glass)

Excellent

Excellent

Weight

Heaviest

Light

Lightest

Impact resistance to large particles/ high Impact

Poor

Good

Best

Thermal Conductivity/ Lenses Steaming up

Fair

Better

Best

Effect on impact resistance of surface scratches sustained through wear and tear

Moderate

Little

Moderate

UV protection    

Greatest

Appearance

Bulky

Better

Best

Minimum centre Thickness of lens

3mm

3mm

2mm

(thinnest)

Chromatic Aberrations (coloured fringes on lens periphery)

Not apparent

Not apparent

Can be disturbing

BOTTOM LINE    

Lenses can be hit with  a hammer and they don’t shatter

 

Other uses

Still used by Rayban, Serengeti et al for sunglasses – superior optical transmission

 

Domed skylights

In case of impact, lenses fracture in manner that
only a few large splinters are produced  which stay within the frame

 

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