1

PHOTOCHROMATIC LENS

MADE BY: SWATI PANARAFROM: BHARTIMAIYA COLLEGE OF

OPTOMETRY2nd YEAR 3rd SEMESTER

2

INTRODUCTION

Photo = lightChrom = colourPhenomenon that color of material is change by

light irradiation. They are lenses that darken on exposure to UV

radiation.

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.

4

OTHER NAME

(1) DAY & NIGHT LENSES

(2) TRANSITION

(3) PHOTO SUN LENSES

HISTORY• INTRODUCED IN 1964, BY DR WH ARMSTEAD AND

SD STOOKEY.• IN 1960 CORNING DEVELOPED 1ST GLASS

PHOTOCHROMATIC LENS• IN 1980 AMERICAN OPTICAL DEVELOP 1ST PLASTIC

PHOTOCHROMATIC LENS (PHOTOLITE LENS)• THEY AWARE LENSES HIGH DARKEN ON EXPOSURE

TO UV (SHORT WAVELENGTH) OR LOW TEMPERATURE.

6

TYPES OF PHOTOCHROMATIC LENS

GLASSPLASTIC

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

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.

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.

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.

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

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.

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

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.

14

15

CHALANGES TO PHOTOCHROMATIC

(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

16

FACTORS AFFECTING TRANSMISSION

1. Intensity: Increase intensity

Increased Darkening

Decreased transmission

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)

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.

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

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 windscreen\green glass absorbs virtually 100% of UV light

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

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.

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.

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.

25

CHARACTARISTIC

• The darkening & fading performance of photo chromatic lenses depends on

- Intensity of UV light, - Exposure memory, - Thickness of lens & - Temperature.

26

Features

1. It darkens to comfortable sunglass in bright sunlight in less than 1min

2. Fades back to virtually clear tint3. 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

27

GRAPHICAL REPRESENTATION

• Darkness

• Transmission

28

DIAGRAM

• Clear Sun Darkens Clear

29

Indoor Outdoor

30

Avability of different company

• Essilor = transitions• German lens (rodenstock) =colormatic• Vision-ease = lifeRx

31

COMPANY

• ESSILOR• KODAK• TRANSITION

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 minutesto fade 80% of the darkened

After > 10 minutes theother photochromic still has a residual colour,it will take more than

> 12 minutesto fade 80% of the darkened

33

Colour changing at the speed of light

Other photochromic

Over 3 minutes

Over 12 min.

34

OtherPhotochromic

35

Otherphotochromic

After 30 seconds

36

OtherPhotochromic

After 60 seconds

37

OtherPhotochromic

After 90 seconds

38

OtherPhotochromic

After 150 seconds

39

Otherphotochromic

After > 10 minutes theother photochromic still has a residual colour,it will take more than

> 12 minutesto fade 80% of the darkened

KODAK InstaShades needs just over

3 minutesto fade 80% of the darkened

40

•THANK YOU