5.1 Designing with Photochromic Materials
5.1.2 Drivewear Photochromic Lens by Younger Optics
Self-darkening sunglasses are probably the best known type of photochromic products since they have a relatively early market exposure, and since they are consumer products rather than scientific or technical products. Such sunglasses have been around in the market since 1966, the date when Corning first introduced the Photograylens (Van Gemert2000). These lenses were made of a borosilicate glass containing fine crystals of copper doped silver halide. Under UV-light, copper (1+) ions give up an electron, which are used by silver cations to form
elemental silver. Silver atoms combine as visible clusters which causes the darkening. The process is reversible, so when the UV-light is reduced or elimi- nated, silver atoms give back one electron and copper (2+) ions are formed. Such lenses still exist today but plastic photochromic lenses reign the market since the 1990s (Erickson 2009). The use of glass lenses for eyewear became a tough challenge after the introduction of new standards by FDA of USA to prevent eye injuries in 1972 because these standards mandated much thicker, thus heavier, glass lenses than used at the time. This meant uncomfortable glasses with thick and Fig. 5.1 Orange Petal Dress; stretch-cotton hand-screen printed. Photochromic screen-print changes fromcleartopurplein sunlight. Metallic goldback-zip andpinksatin trim. Photo by Cereinyn Ord.CourtesyAmy Winters
Fig. 5.2 Tropical Storm Skirt;orange nylontaffeta, triangular panel, sublimation print. Photochromic screen- printed design changes from cleartopurplein sunlight, here shown after exposure.
Photo by Cereinyn Ord.
CourtesyAmy Winters
Fig. 5.3 BlueLightning Swimsuit;bluepolyester/elastane colour-gradient sublimation printed.
Triangular paneled lightning print, central panel printed with sun-reactive dot pattern.
Photochromic ink screen-print changes from clear to purple in sunlight, here shown after exposure. Photo by Cereinyn Ord.CourtesyAmy Winters
Fig. 5.4 Rainforest Dress; sculptural tulip-shape dress with 3-D flowers. Flowers multi-colored, pinkandbluewithwhitehydrochromic ink overlay and photochromic ink.Greencolor-gradient print bodice withwhitehydrochromic ink overlay, machine embroidered panels andpinkskirt.
Hydrochromic ink becomes transparent on reaction to water revealing the colored print underneath. Photochromic flowers change fromcleartopurplein sunlight. Photo by Cereinyn Ord.CourtesyAmy Winters
heavy lenses. This challenge was met by the introduction of plastic lenses by PPG Industries, which employed a thermoset with the trademark CR-39. Plastic photochromic lenses were introduced to the market in 1982 by American Optical with the trademark Photolite. In these lenses, indolinonaphthoxazines were used for the darkening effect. This product was not successful in the market due to the blue color produced in the darkened state, instead of the more neutral gray or brown colors people were accustomed to. Subsequent generations employed naphthopyrans and indenonaphthopyrans. The molecular structure of naphthopy- rans change under UV-light by the breakage of a weak chemical bond. The rearranged molecules absorb visible light. While these sunglasses perform well in daylight, they cannot provide the same effect inside the car because windshields contain UV-blocking agents. This was the driving force behind the development of Drivewearby Younger Optics in collaboration with Transitions Optical.
Driving is a complex activity involving multitasking and the processing of a great deal of information in a short time. This situation is further complicated by changes in road conditions, weather condition, traffic conditions, and occasional obstacles (Fig.5.6). All such information is captured by the driver’s eyes.
Therefore, unfavorable light conditions such as bright light or glare create risks for the driver. The combination of Transition Optical’s photochromic technologies and Younger Optics’ polarizing solutions provide optimum vision when driving in low light or full sunlight, or when the user is outside the car (Younger Optics 2012).
Advanced photochromic dyes provide auto-darkening effect both inside and outside the car, responding to visible as well as UV radiation. The polarization Fig. 5.5 Rainforest
Swimsuit;purplepolyester/
elastane color- gradient sublimation print.White graphic screen print in hydrochromic ink. Thewhite print disappears on reaction to water, here shown before exposure to water. Photo by Cereinyn Ord.CourtesyAmy Winters
technology adapted to Drivewearhas the ability to work well not only when the lenses are dark, as in competing products, but also when there is overcast weather and the lenses are clear (Figs.5.6, 5.7). Under overcast low light conditions, Drivewearlenses allow high light transmission and prevent any possible glare.
Fig. 5.6 Challenging driving conditions and their perception by the eye (top). The state of different layers of Drivewearlenses under various light conditions (bottom).CourtesyYounger Mfg. Co
Fig. 5.7 Simulation of Drivewear lenses under different outdoors and driving conditions.
CourtesyYounger Mfg. Co
The color at this stage is green to yellow. When bright sunlight hits the windshield, a smaller fraction of the light is allowed to pass through the lenses, now copper- colored, relieving the eyes from strain. Outside the car, the lenses become dark reddish brown and achieve their darkest color. Glare is prevented with polarized lenses under all conditions.