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Photochromatic lenses
1) Photochromic lenses are lenses that darken when exposed to UV light and fade back to clear when removed from the light. They help the eyes adapt to changing light conditions both indoors and outdoors. 2) There are two main types of photochromic lenses - glass and plastic. Glass uses silver halide crystals while plastic uses spiroxazine molecules. Both darken when activated by UV rays and fade when the UV exposure is removed. 3) Factors like temperature, thickness, intensity of UV light, and exposure history affect how quickly and darkly the lenses change color. Photochromic lenses provide eye comfort in varying light but have some limitations like delayed response time and gradual loss of darkening ability over
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Photochromatic lenses
- 1. MADE BY: SWATIPANARA FROM: BHARTIMAIYA COLLEGE OF OPTOMETRY 2nd YEAR 3rd SEMESTER 1
- 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. 2
- 3. Whether You glassesor 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. 3
- 4. OTHER NAME (1) DAY& NIGHT LENSES (2) TRANSITION (3) PHOTO SUN LENSES 4
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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 7
- 8. How the processof 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. 8
- 9. • Each glasseshas 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. 9
- 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. 10
- 11. Corning • Glass workhave 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 11
- 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. 12
- 13. • When activatedby 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 13
- 14. TRANSITION CORNING Photochromic witha 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 ONUV (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 15
- 16. FACTORS AFFECTING TRANSMISSION 1.Intensity: Increase intensity Increased Darkening Decreased transmission 16
- 17. FACTORS 2 λ ofIncident 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) 17
- 18. FACTORS 3 Temperature: Lowerthe 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. 18
- 19. Advantage • Photo chromaticlenses 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 19
- 20. Disadvantage • The mainlydisadvantages 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 20
- 21. • It graduallyloses 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 21
- 22. DISPENSING TIPS • Photochromatic 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. 22
- 23. • Photo chromaticdo 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. 23
- 24. USEFUL KEY TOAVOID 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. 24
- 25. CHARACTARISTIC • The darkening& fading performance of photo chromatic lenses depends on - Intensity of UV light, - Exposure memory, - Thickness of lens & - Temperature. 25
- 26. Features 1. It darkensto 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 26
- 27. GRAPHICAL REPRESENTATION • Darkness •Transmission 27
- 28. DIAGRAM • Clear SunDarkens Clear 28
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- 30. Avability of differentcompany • Essilor = transitions • German lens (rodenstock) =colormatic • Vision-ease = lifeRx 30
- 31. COMPANY • ESSILOR • KODAK •TRANSITION 31
- 32. Color changing atthe 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 32
- 33. Colour changing atthe speed of light Other photochromic Over 3 minutes Over 12 min. 33
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- 39. Other photochromic After > 10minutes 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
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