The black shaded glasses that turn darker in the sun are called photochromic lenses, also known as transition lenses. They are eyeglass lenses that automatically change tint depending on the amount of ultraviolet (UV) radiation present. When exposed to UV light, the lenses darken in color providing protection from harsh sunlight. Indoors or in low light conditions, the lenses become clear again allowing for comfortable vision. Photochromic lenses offer the convenience of glasses that can adapt to various lighting conditions, eliminating the need for separate prescription sunglasses and reducing eye strain.
How Do Photochromic Lenses Work?
Photochromic lenses contain special molecules that are activated by UV light. These molecules are reversible, meaning they can switch between two states in response to the presence or absence of UV light. Here is a brief overview of how the photochromic technology works:
| In the Absence of UV Light | In the Presence of UV Light |
|---|---|
| The photochromic molecules remain in their transparent, relaxed state. | The UV light causes the molecules to change shape into their activated, darkened state. |
| The lenses stay clear allowing comfortable indoor vision. | The lenses darken in color to block bright sunlight outdoors. |
When the UV light source is removed and the lenses are brought back indoors, the photochromic molecules revert to their original inactive state and the lenses become clear again. This activation-relaxation process can repeat over and over allowing the lenses to continuously adapt to changing light conditions throughout the day.
Types of Photochromic Lenses
There are a few different types of photochromic lenses available. They differ based on the specific photochromic dyes or molecules they use. Here are some of the main types:
1. Organic Photochromic Dyes
Organic dyes were the first photochromic molecules used in eyeglass lenses. Some common organic dyes used include naphthopyrans and spirooxazines. Organic dyes provide good darkness activation and acceptable fade-back speed. The organic molecules can stop functioning over time with extended UV exposure.
2. Inorganic Photochromic Crystals
Inorganic photochromic lenses use special photochromic crystals made from silver halides. The crystals contain silver atoms that rearrange when exposed to UV light causing the lens to darken. Inorganic crystals offer improved longevity over organic dyes. However, they take longer to fade back and may not get as dark.
3. Combination of Organic and Inorganic
Some photochromic lenses combine both organic dyes and inorganic crystals. This hybrid approach aims to provide the best features of both technologies. The lenses activate and fade back quickly while also resisting degradation over time. Brands like Transitions Optical use a combination approach.
4. Thermochromic Photochromic
A newer type of photochromic lens uses thermochromic technology in addition to photochromic dyes. Thermochromic materials change properties based on temperature. Adding a thermochromic component causes the lenses to get darker with both UV and heat exposure. This provides faster activation and added comfort in hot, sunny conditions.
Advantages of Photochromic Lenses
Here are some of the main benefits that photochromic eyeglass lenses can provide:
– Convenience – Single pair handles various light conditions. Don’t need dedicated sunglasses.
– Comfort – Eyes adjust naturally without having to switch glasses. Reduces eye fatigue.
– UV protection – Lenses darken to filter UV and block harsh sunlight when outdoors.
– Glare reduction – Tinting cuts down on blinding glare for improved visibility.
– Versatility – Can be used for both prescription eyeglasses and non-prescription sunglasses.
– Automatic operation – Lenses change on their own without user input required.
– Customizable – Different dye types, tints, and intensities available.
– Improved safety – Don’t have to take eyes off the road to swap glasses.
Disadvantages of Photochromic Lenses
While photochromic lenses have their benefits, there are also some potential disadvantages to consider:
– Slow transition indoors – Can take up to 10 minutes to completely clear after coming inside.
– Temperature dependence – Won’t activate fully on cold winter days. Heat speeds up transitions.
– Incomplete darkening – May not get as dark as regular sunglass lenses in very bright light.
– Added cost – More expensive than regular clear eyeglass lenses.
– Reduced durability – Photochromic dyes can degrade over time with prolonged UV exposure.
– Limited activation in cars – Most auto windshields block a lot of the UV light required.
– Unsuitable for some wearers – Not recommended for those with light sensitivity disorders.
– Appearance – Some users dislike the look of the tint indoors and prefer fixed tint sunglasses.
Ideal Candidates for Photochromic Lenses
While photochromic lenses work for many eyeglass wearers, there are certain groups that can benefit the most:
– Adults over 40 – Susceptible to UV damage, glare, and eye fatigue.
– Active individuals – Frequent outdoor recreation like sports, hiking, water activities.
– Drivers – Especially long distance driving like road trips, trucking, etc.
– Variable schedule – Occupations with indoor and outdoor components.
– Minimal sunglass users – Don’t like carrying or switching to sunglasses.
– Parents of young children – Handling kids in and out of sunlight throughout the day.
– Light sensitive – Conditions like migraine disorders aggravated by light changes.
– Lazy swappers – Those resistant to carrying and swapping between two pairs of glasses.
– Affluent users – Willing to pay more for premium convenience and eye protection.
Popular Photochromic Lens Brands
There are a number of companies that manufacture quality photochromic lenses and eyewear. Some of the major brand names to look for include:
– Transitions – The biggest player in the market. Makes the leading photochromic lenses. Owned by Essilor.
– Hoya – Multinational company producing Vision Care products including photochromic lenses.
– Zeiss – German optics company with photochromic lenses under brands like PhotoFusion and PhotoFusion Plus.
– Kodak – Offers Kodak Total Blue and other Kodak Vision photochromic lens products.
– Vision-Ease – Major optical products company with LifeRx photochromic lenses.
– Younger Optics – Makes the NuPolar photochromic lens brand.
– Corning – Leading glass manufacturer with photochromic SunSensors brand.
– SEIKO – Japanese company that produces quality photochromic lenses.
– Rodenstock – German optics firm with Impression photochromic lenses.
How to Choose Photochromic Lenses
If you are considering photochromic lenses, here are some tips for selecting the best option:
– Get professional help – Consult an optometrist or optician to pick the right lenses for your needs and prescription.
– Prioritize eye health – Ensure the lenses offer full UV protection and glare reduction.
– Consider activities – Will they be used for sports, driving, work? Pick suitable darkness and speed.
– Evaluate lighting conditions – Frequent use indoors or outdoors? Weigh tinting behavior.
– Review lens materials – Look at lens substrate like polycarbonate, Trivex, etc.
– Choose lens treatments – Anti-reflective and scratch-resistant coatings are recommended.
– Compare brands and prices – Transitions, Hoya, Zeiss and others have options at different price points.
– Read third party reviews – Check independent evaluations online and in publications.
– Try before you buy – See if you can test out the lenses first to evaluate performance and comfort.
Frequently Asked Questions
Here are answers to some common questions about photochromic lenses:
How long do photochromic lenses last?
Most photochromic lenses remain effective for 2-3 years with proper wear and care. Gradually the molecules lose their activation ability requiring lens replacement.
Do photochromic lenses work in the car?
Due to the UV blocking properties of most auto windshields, photochromic lenses only partially activate in the car and do not get very dark. Special car photochromic lenses are available to address this issue.
Can photochromic lenses get too dark?
No, there are limits built into the dyes and crystals that prevent the lenses from exceeding the darkest tints for safe everyday use. However, they may not darken fully in extremely bright light.
Do photochromic lenses work for bifocals or progressives?
Yes, you can get photochromic lenses for multifocal prescriptions. The light-reactive tinting will work across the entire lens including distance, intermediate, and reading sections.
Do photochromic lenses come in different colors?
Yes, gray, brown, and amber photochromic tints are available. Gray is the most common while brown and amber provide a more natural, sunglass-like appearance.
Conclusion
Photochromic eyeglass lenses offer a functional way to maintain comfortable vision in changing light. The lenses conveniently darken when you head outdoors and return clear when you go back inside. With the benefits of UV protection, reduced glare, and all-day wearability, photochromic lenses provide an effective single pair solution for eyeglass wearers with active lifestyles. While not ideal for every user, photochromic lenses eliminate the hassle of constantly switching glasses and can enhance safety, comfort, and performance in variable lighting circumstances. With a basic understanding of the technology and options available, you can decide if this innovative eyewear solution is right for your eyes and lifestyle.