1. MADE BY: SWATI PANARA
FROM: BHARTIMAIYA COLLEGE OF
OPTOMETRY
2nd YEAR 3rd SEMESTER
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2. INTRODUCTION
Photo = light
Chrom = colour
Phenomenon that color of material is change by
light irradiation.
They are lenses that darken on exposure to UV
radiation.
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3. Whether You glasses or not, eyes experience
eyestrain E.g. TV, computer, reading, sunlight.
Etc. causing eye strain and watering.
Photo Chromatic lenses can help your eyes to
cope up as they react to different light
conditions during the day .
Gives a visual comfort whether indoors or
outdoors.
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7. GLASS PHOTOCHROMATIC LENSES
• It contains microscopic crystal size about 5nm
in diameter of “Silver Halides” (usually Silver
Chloride).
• Silver Halide crystals doped with Copper are
mixed in with the glass at the time of
manufacture and in the Borosilicate mixture
used by Corning.
• It can be represented as :-
Ag + Cu + UV Ag + Cu
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8. How the process of darkening and fading
occurs?
• When Silver Halide are exposed to UV rays or blue
light of visible spectrum (range 300-400nm), breaks
into Silver and Halogen leading to darkening process.
• As Silver is sets free it give rise to dark colour.
• As Halogen is held within the glass and combined
with Silver on removal of UV rays, the lens return
back to its original colour i.e. the process of fading
takes placed.
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9. • Each glasses has got its own transmission
range, fading range and reaction time.
• Transmission rates indicates the maximum
(fully faded) and minimum (fully darkened)
transmission of UV rays and is written in
fraction
for e.g.- 80/45
• Fading rate indicates the time taken to fade
back to 70% of original transmission value.
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10. • Reaction time (Darkening process) is the time
taken to darkened completely.
• Darkened and fading process depend on
temperature also.
• Best line glasses has a refractive index 1.523
and is colourless in its inactivated stage,
becomes a pale brown colour on exposure to
light.
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11. Corning
• Glass work have introduced photogrey which
darkened to grey tint on exposure to UV rays
and slightly pinkish tint in its inactivated stage.
• It is most sensitive to the wave length.
350 – 360 nm
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12. PLASTIC PHOTOCHROMIC LENSES
• ESSILOR OPTICAL & PPG Industries combines in 1990
to produce plastic photo chromic lens known as
TRANSITION LENS the second generation of this lens
is now called as the TRANSITION COMFORT LENS.
• Rather than making use of silver halide crystal this
lenses owes its darkening to the presence of SPIRO
INDOLINE MOLECULES.
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13. • When activated by UV rays in sunlight the
spiro-indoline molecules scatters absorbing
sunlight and reducing the amount of visible
light generates the lens
• When the lens is removed from sunlight the
chemical reaction reverse and the lens return
to its clear states
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14. TRANSITION CORNING
Photochromic with a narrow
variation in transmission between
the faded and darkened states are
promoted for the use in the city
where light condition changes
quickly between outdoors and
indoor.
Photochromic with a wider
variation in transmission between
the faded and darkened states are
suitable for a narrow range of
prescription as the variation tint
density across the lens is more
apparent.
Property:- They does not loose
their photochromic effect even
after 3-4 years.
Property:- They loose their
photochromic effect even after 3-4
years.
If one of the glass in a spectacle is
broken then the option of changes
the broken glass only and
maintaining the colour between
both the glasses can be possible.
If one of the glass in a spectacle is
broken then the option of changes
the broken glass only and
maintaining the colour between
both the glasses can not be
possible.
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15. CHALANGES TOPHOTOCHROMATIC
(1)DEPENDENT ON UV
(2)UV SPECTRUM CHANGE DURING THE DAY
(3)VARIATION OF UV-A PRESENT DURING THE
DAY.
(4)AMOUNT OF ACTIVATING UV NEEDED.
(5)LIFE OF PHOTOCHROMATIC SUBSTANCE
(6)MEMORY
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17. FACTORS
2 λ of Incident radiation: Short λ, Increases
darkening. While it also depends on the
material E.g.
1 Agcl2 350nm λ causes darkening.
2 AgBr2 550nm λ causes darkening.
3 AgI2 650nm λ causes darkening.
(Most commonly used is AgCl2)
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18. FACTORS
3 Temperature: Lower the temp, faster and
deeper the darkening.
4 Thickness: More the thickness i.e. more
material, more the darkening.
5 Exposure: Newer lenses take time to darken.
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19. Advantage
• Photo chromatic lenses can help your eyes to cope up as
they react to different light conditions during the day
• Good Photo chromatic lenses blocks 100%ofmost harmful
radiation
• Protects you from UV which can cause lost of harm to eye
specially cornea & conjunctiva
• Gives a visual comfort whether indoor or out door
• Photo chromic are available in single vision, bifocal and
varifocal forms
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20. Disadvantage
• The mainly disadvantages of the photochromic
lenses is they do not adjust immediately.
• It could take up to two minutes for the lenses to
adequately change from light to dark or vice
versa
• Another disadvantage for some users is that
they will not darken when worn inside vehicles
because windscreengreen glass absorbs
virtually 100% of UV light
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21. • It gradually loses its darkening ability with
time.
• However , if the lenses are worn no longer
than about 2 years.
• The decreased darkening is not likely to be to
be noticed by the wearer
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22. DISPENSING TIPS
• Photo chromatic lenses are not as effective in
hot climate.
• When temperature increase , the reaction
slows.
• So , they are not recommended to replace
sunglasses.
• Photo chromatic lenses do not lighten
instantaneously when going from a bright to a
dim area.
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23. • Photo chromatic do not always return to their
maximum transmission , the additional
reduction in illumination when driving at night
may prove hazardous.
• Anti reflection coating will not reduce the
range of the photo chromic cycles but as with
any lens , will increase the transmission in
both the lightened and darkened status.
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24. USEFUL KEY TO AVOID PROBLEM
• (1)always make sure that the new lens is of
the same type as the old lens , i.e. , same
brand , same thickness etc.
• (2)if the old lens has been chemtemperated ,
have it re-strengthened along with as the new
lens.
• (3)if the old lens has not been treated in
anyway , place it with the new lens in boiling
water for half an hour.
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25. CHARACTARISTIC
• The darkening & fading performance of photo
chromatic lenses depends on
- Intensity of UV light,
- Exposure memory,
- Thickness of lens &
- Temperature.
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26. Features
1. It darkens to comfortable sunglass in bright
sunlight in less than 1min
2. Fades back to virtually clear tint
3. Light transmition is automatically adjusted
to brightness of sunlight.
4. Photo chromatic lenses must be darken and
faded through many cycles to achieve
maximum performance
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32. Color changing at the speed of
light
• 3 minutes in Kodak institute shades.
• Other photochromatic lenses over 12
minutes.
KODAK InstaShades
needs just over
3 minutes
to fade 80% of the darkened
After > 10 minutes the
other photochromic
still has a residual colour,
it will take more than
> 12 minutes
to fade 80% of the darkened
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33. Colour changing at the speed of light
Other photochromic
Over 3 minutes
Over 12 min.
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39. Other
photochromic
After > 10 minutes the
other photochromic
still has a residual colour,
it will take more than
> 12 minutes
to fade 80% of the darkened
KODAK InstaShades
needs just over
3 minutes
to fade 80% of the darkened39
