Photochromatic lenses and tints www.eyenirvaan.com

PHOTOCHROMATIC
LENSES AND TINTS
Gopi Vankudre M. Optom, FIACLE
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PHOTOCHROMATIC LENSES
AND TINTS

The Photochromatics
 Invented 1964 by Corning
 Available as
– Glass Photocromatics
– Plastic Photocromatics

Glass Photochromatics
Consist of silver halides
Activated by UV radiations between 300-
400nm
Do not wear out with repeated darkening
and lightening
But the lenses do not lighten indoors

Plastic Photochromatics
Uses Organic crystals instead of In-
organic crystals
Consist of Indolino spiroresines(ISN)

Different manufacturing methods
 Imbibition
 In-mass
 Multimatrix
 Dip Coating
 Front surface coating
 Transbonding

Imbibition
 Used by Transitions
 Starts with clear plastic lens
 The surface is infused with photochromatic
material

In-Mass
 Phtochroamtic dye is mixed in the liquid
monomer
 This is similar to glass photochromatics
 In glass
– The material reacts throughout the lens
– Gives Bulls’s Eye effect

In-Mass
 In Plastic:
– Does not produce the Bulls Eye effect
– When the dye near the surface wear out , the dye
within matrix absorbs UV
– E.g: Corning Sunsensors, Rodenstock ColorMatic

Dip coating, Front Surface coating,
Transbonding
 Not very commonly used
 Transbonding: Used for Polycarbonate and
High-Index material

Multimatrix
 Used by Kodak Insta-shades
 Begins with clear lens
 Has 1 mm photochromatic dye bonded to it

Advantages and disadvantages
of Photochromics
 Glass- 100% UV B and 98% UV A absrption
 Plastic Photochromics wear out – depends
on number of UV exposures
 Glass photochromic fail to fully lighten
 They do not replace the sunglasses- For e.g.
for person driving a car

Factors Influencing
Photochromatic Performance
 Both glass and plastic
– Light Intensity
– Temperature
 Glass
– Previous exposures
– Lens thickness
 A PG extra lens has 22% transmission for 2mm
thickness and 11% for 4mm
– Toughening Process

Toughening and Photo
chromatic effect
 Photo chromic lenses should be chemically
toughened
 Heat hardened lens lightened slower
 Also reduces the transmission in the darken
stage.

When Replacing One Glass
Lens
 Ideally replace both the lenses
 If new lens is hardened , also harden the old
lens
 Boil the old lens in water for 2 hours
 Keep the lens in oven at a temperature of
212˚F
 A heat lamp may also be used

Color Coatings
 Metallic oxides are used for absorptive
coating
 Advantage
– May be removed and recoated
– Transmission curve are more even
– Absorbs the longer wavelength in the near IR
region

Glass color coatings
 Glass color coatings
– Coating is uniform regardless the prescription
 Color coatings for Plastic Lenses
– Plastic lenses are normally dyed and not coated
– However CR-39, plastic and high – index material
can be color coated

Dying plastic lenses
 Versatility of tinting
 Longer it is kept in dye darker the tint
 Dye is absorbed over the surface equally
 Disadvantage of poor IR absoption

Gradient lenses
 Darker upper portion
 Lighter lower portion
 Produced in plastics

Color characteristics
 Clear crown glass and cr-39
– Crown glass absorbs light below 290 nm
– Cr39 has UV inhibitor blocks UV below 350 nm
 Pink
– Has uniform transmission
– Do not cause color distortion
– Reduces internal reflections

 Yellow
– Absorb shorter visible light
– Should not be adviced at night
– Increases contrast
– Common brand names are Hazemaster (AO) and
Kalichrome (B & L)

 Brown
– Same characteristic of absorbing short
wavelength as of yellow tint
– Used to improve contrast in bright , hazy and
smoggy days

 Green
– Has similar color sensitivity curve as for the
humen eye
– Contains ferrous(iron) oxides
– Good absorption in UV and IR region

 Grey
– Most popular for sun protection
– Evenness of transmission
– Does not cause misjudgment in color vision
deficient’s

THANK YOU

Photochromatic lenses and tints www.eyenirvaan.com

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