Case Study: Photochromic Lenses
From a Council on Competitiveness HPC Case Study
Transitions lenses are made by Transitions Optical, Inc. a joint venture formed in 1990 by PPG Industries of Pittsburgh and Essilor International of Paris. Based on proprietary photochromic technology, the lenses quickly change from clear to dark in the presence of ultraviolet light and block 100-percent of harmful UVA and UVB rays. The transition is the result of photochromic dyes. When exposed to ultraviolet light, the dyes' molecular bonds break and the molecular structure changes, which in turn changes the lens color and provides UV protection. Remove the UV, and the lenses quickly return to a colorless state.
The development of successive generations of photochromic lenses has been based in large part on PPG research. Beginning several years ago, Jun Deng and Michael Makowski, scientists in PPG's computational-chemistry research group, faced a challenge in eyewear: meeting market demands for improved photochromic technologies for a high-growth segment within the ophthalmic lens market using new impact-resistant, high-index and polycarbonate materials.
One of the main differentiators among lenses that "transition" is the performance of the photochromic dyes - how fast the lenses shift from light to dark and back again, how dark the lenses can become when exposed to UV light and the color itself - brown and gray are good, hot pink or dark purple not so good. How long the product will last before the photochromic coating begins to lose its effectiveness is also key to product success. "With each successive generation," says Makowski, "you want to develop a product that has better performance, is robust to various substrates and processing, and has a lower price tag." Essentially, it's a scientific problem. In order to advance photochromic dyes and coatings, PPG had to understand what was going on not only at the molecular level (between dyes and their matrix), but also at the quantum level (electronic structure), which dictates the dyes' behavior when they interact with light.
To physically synthesize and test a new dye can take weeks to months, and PPG needed to examine many materials. Computational research was key to fast time-to-market, but PPG soon found that the quantum-chemistry problems it wanted to tackle were too computationally intensive for their in-house systems. By joining PSC's industrial affiliates program, PPG gained access not only to PSC computational resources but also to the expertise of PSC personnel. A complex calculation that might have taken a week on PPG's in-house machines - if it could be run at all, says Makowski, now takes only several hours.
This permits PPG to predict many performance characteristics of molecular structures under a variety of conditions, without having to construct a physical prototype. "We can computationally screen a whole series or family of new structures proposed by our organic chemists," says Makowski, "and weed out the 80-percent that will ultimately fail when they are tested experimentally."
With PSC resources doing quantum calculations, PPG brought its new fifth-generation photochromic technology to market ahead of competitors, gaining market share and increased sales and earnings. Ongoing work now continues and PPG's sixth-generation product is slated for launch within the next year.