Since their introduction, demand for photochromic lenses—lenses that change color based on sun exposure—has risen dramatically; today, these types of lenses account for nearly 16% of all eyeglasses purchased in the US annually.1 Those whose vision requires constant correction in particular often opt for this type of eyewear to avoid the need for a separate pair of sunglasses and customers depend on their lenses to be durable, long-lasting, and to accurately transition in a way which is seamless and unobtrusive. Manufacturers provide this by creating complex color layers that work together to create a unique result.
However, lenses that transition aren’t as easy to create as standard clear lenses. Working with multiple colors and dyes can present unique challenges to the manufacturing process, as each additional step opens up room for potential error. To minimize errors and create perfect combinations, some manufacturers rely on the advanced technology of spectrophotometers as an integral part of product development and production.
Layering Dyes to Create Photochromic Lenses
Adaptable lenses are produced using photochromic dyes which change color when exposed to UV light. However, it’s not just the type of dye that creates this effect, but the changes made through a unique series of different colored layers, which are arranged to ensure that the transition from dark to light is gradual and functional. And there is no single standard dye; the biggest manufacturer of adaptive lenses in the US, Transitions Optical, reports more than 3000 different patented dyes.2. This wide range of dyes is needed to create successful transitions, which are achieved by layering dyes on top of each other.
Creating high-quality adaptable lenses requires a high level of color precision to ensure that the lenses behave as desired. However, the nature of the materials and the products present a number of challenges in the color measurement process:
- Minimal testing window: These lenses must be tested based on their transition following exposure to UV light. As soon as that UV source is removed from the process, the lens will begin to return to its original clear appearance. This makes it challenging to pinpoint testing during the process, as the color is always changing slightly.
- High-stake results: Lenses that can rapidly fade from dark to light and vice versa aren’t just fashionable, they also play an important role in protecting health and well-being by reducing eye strain and minimizing exposure to harmful UV rays. At the same time, these lenses need to stay clear enough to allow users full visibility, especially when driving.
- Gloss: All lenses have a gloss to them and this gloss can affect the appearance of color, potentially complicating color measurement.
It’s important that color is tested after the lens is made to ensure that it’s both aesthetically appealing and properly manufactured. A manufacturer wouldn’t want a customer’s lenses to turn pitch black suddenly as they’re driving, nor would they want those lenses to turn a sickly shade of green after a day at the beach. Spectrophotometric color measurement is the only way to verify this will not happen. So while color measurement may present challenges for lens manufacturers, it’s also an absolute necessity.
Using Spectrophotometers in the Creation of Adaptable Lenses
Modern spectrophotometric instrumentation allows you to overcome the challenges of color analysis in adaptable lenses by offering state-of-the-art technologies designed to optimize color measurement accuracy and efficiency. This instrumentation plays a critical role at multiple points in the production process, including the manufacturing of dyes and the lenses themselves. Significantly, spectrophotometers can be used to measure transitional lenses during specific stages of exposure to correlate dyes and light levels to color state. This gives you the ability to determine correctness of processing and refine manufacturing practices to optimize product quality. The rapidity of measurement means that the color may be analyzed before it has the opportunity to change; if the light in the laboratory is controlled to induce transitional states, you will be able to obtain accurate color measurements even when lens itself is briefly exposed to the light of spectrophotometer due to the time required for color changes to take place.
When working with the glossy surface of an adaptable lens, a spherical instrument operated in transmission mode allows you to obtain the most accurate measurements. These spectrophotometers address factors such as light reflection to ensure gloss does not interfere with color analysis and allow you to tightly control measurement conditions. Due to the curvature of the lens, you may need to rotate the sample and obtain multiple readings in order to gain meaningful color data.
Using spectrophotometers, manufacturers can eliminate errors in the dye manufacturing and layering process to create the precise transitions customers are looking for. These instruments significantly enhance your ability to manage production, spot check quality, and ensure errors are eliminated, ultimately improving the quality of your products. This is particularly critical with vision aids like adaptable lenses; your products shape the way your customers see the world and maintaining the most rigorous color quality control processes is essential to ensure they can rely on you to meet their medical needs.
For over 60 years, HunterLab has been an industry leader in the creation of color measurement technology. Today, we offer a provide a comprehensive range of portable, benchtop, and on-line spectrophotometers developed to meet the needs of our customers in a wide variety of industries, including lens manufacturing. Contact us to learn about how our renowned instruments, customizable software packages, and world-class customer support services can help simplify the complexities of adaptive lens creation.