We’ve all experienced being temporarily unable to focus our eyes and see clearly when stepping out into the sunshine. It’s frustrating, disorienting, and can be dangerous. What’s even more frustrating, however, is having to switch between clear and gray safety glasses when heading outside. During these transitions, you may find yourself forgetting one pair or the other, then get stuck indoors or outdoors without the correct lens.
Available now in MCR Safety glasses - VL220PCPF
Photochromic lenses for glasses were originally introduced in 1966 by Corning Glass Works. There it was discovered that when silver-based crystals were applied to the molten glass, the finished lenses would darken in response to UV light in just a few minutes. The more intense the UV exposure, the darker the lenses would become, and they would continue to adjust in a variety of light conditions. The lenses are clear (or nearly clear) indoors and darken automatically when exposed to sunlight. You can see how this type of lens technology would be advantageous for someone wanting to eliminate the need for carrying both a clear and gray set of safety glasses.
Since these lenses were developed, light-responsive technology has seen significant improvements in performance. As a result of these improvements and our ability to improve manufacturing efficiencies, MCR Safety has developed our first affordable photochromic safety glasses. Below is everything you need to know about MCR Safety’s photochromic lenses.
How They Work: The Technology
You may hear safety glasses referred to as having "auto-tinting lenses", "light-adaptive lenses", “transition lenses”, or "variable tint lenses". If you’re considering photochromic lenses, or already have a pair, you may be wondering exactly how they become darker or lighter. The safety glass achieves its photochromic properties through the embedding of molecules into the lenses, which allows for reversible darkening capabilities. These molecules change shape when activated by the sun's ultraviolet radiation, causing them to automatically darken. As the presence of UV light decreases, the lenses will adapt and become clear again.
As the sun’s UV light shines on the lens, auto-darkening technology is activated
Photochromic lenses darken faster than they turn back to clear. If you have a pair, you’ve probably noticed that darkening generally happens pretty quickly. However, the chemical change of the molecules back to their inert clear form happens more slowly. We cover more on VLT and the specific transition times next.
MCR Safety’s Technology and the Importance of VLT
When thinking about any pair of safety glasses, it’s important to pay attention to the amount of Visible Light Transition (VLT) that is offered. The amount of visible light that passes through each lens affects one’s vision and are necessary factors to consider when purchasing safety glasses. Different applications and environments call for different lenses, such as an amber lens being required for low-light environments. ANSI, the American National Standards Institute, provides guidelines for clear- and filter-plano (non-prescription) lenses in its Z87.1-2015 edition.
Here are the standard VLTs for both clear and gray safety glasses:
- 90% of visible light is transmitted
- 13% of visible light is transmitted
When considering safety glasses with photochromic lenses, it is also important to know how long it takes for the lenses to transition between clear and gray, and the amount of VLT offered by the lenses as time progresses.
When transitioning from clear to gray
As you can see from the numbers below, it does not take long when transitioning from clear to gray:
- At 0 seconds, there is 84.8% VLT
- At 5 seconds, there is 48% VLT
- At 10 seconds, there is 28.5% VLT
- At 15 seconds, there is 20.5% VLT
- At 20 seconds, there is 18.4% VLT
- At 25 seconds, there is 16.8% VLT
- At 30 seconds, there is 15.8 % VLT
VLT when a lens is at full gray is more of a medium gray, due to it not reaching a full 13% VLT.
When transitioning from gray to clear
One thing stands out from the numbers below: it takes longer to reach clear going from a gray lens. Here are the VLT measurements as they transition:
- At 0 seconds, there is 14.4% VLT
- At 10 seconds, there is 20.3% VLT
- At 30 seconds, there is 33.7% VLT
- At 40 seconds, there is 39.6% VLT
- At 50 seconds, there is 44.7% VLT
- At 60 seconds, there is 48.9% VLT
- At 70 seconds, there is 53.5% VLT
- At 80 seconds, there is 57.1% VLT
- At 90 seconds, there is 60.1% VLT
- At 100 seconds, there is 62.7% VLT
- At 110 seconds, there is 64.9% VLT
- At 120 seconds, there is 66.8% VLT
- At 130 seconds, there is 68.4% VLT
- At 140 seconds, there is 69.8% VLT
- At 150 seconds, there is 71% VLT
- At 160 seconds, there is 72% VLT
- At 170 seconds, there is 72.8% VLT
- At 180 seconds, there is 73.5% VLT
To reach 84.8% VLT (full) clear, a lens will take a total of 5 minutes transition time. So, anyone needing fast acting clear glasses should maybe think twice about selecting a photochomic lens.
Temperature Dependency - Two Important Factors
Photochromic lenses are temperature-dependent, which means transitional performance varies. So, it’s important to remember these two factors when thinking about transition time:
- Photochromic lens performance is affected by local hot temperatures and humidity, meaning the safety glass' lens will not be as dark.
- Photochromic lenses for glasses are more effective in colder temperatures, meaning the safety glass lens will get darker.
Photochromic lenses darken faster in colder conditions.
As discussed in the following article, photochromic lenses perform perfectly at around 40-45F, on a clear day and with low humidity. However, once temperatures reach 100, transmittance performance is cut essentially in half. This means it will be difficult for transition safety glasses to achieve the same darkness as a standard gray safety glasses if they are worn in warm temperatures. On the flip side, these lenses darken faster in colder temperatures.
Advantages and Disadvantages
Our goal is to educate, which means we want users to take in all pertinent information before making a decision. There are benefits and drawbacks to photochromic lenses, so you will need to decide whether these glasses are the right choice for you. In some cases, photochromic lenses are not an ideal choice, especially if most work is performed only indoors. For example, the U.S. Army has declared safety glasses with photrohrochromic lenses nay not be worn indoors due to the slow rate of change from gray to clear.
Here is what you need to consider:
Advantages of Photochromic Lenses
- Provides comfortable all-day vision. As the daylight levels change, these glasses change with the time.
- Allow you to navigate the workplace with one set of safety glasses. Glasses automatically adapt to changes in light conditions. You can wear them both indoors and outdoors, rather than needing to switch between two pairs of glasses (this also means you’ll be less likely to lose them).
- They offer 100% protection against harmful UVA, UVB, and UVC rays.
Disadvantages to Photochromic Lenses
- Even when fully activated, the lenses don’t become as dark as traditional gray safety glasses.
- The amount of time needed to darken is impacted by the temperature and humidity, performing best in colder temperatures.
- Why don’t they work in my vehicle? Because windshields are designed to block most UV light, the lenses won’t darken because they can’t be activated.
We are not trying to discourage you here, just laying out what you need to consider before making a purchase. The last thing we want is an upset user, only because we failed to lay out everything one should know.
One more “pro” before we move on: these glasses are great for sports activities, such as bicycling. Early morning rides, before the sun is all the way up, require clear glasses. However, once that sun starts to come up, you need to transition into a gray lens. This means they’re also great for riding motorcycles. Don’t get caught riding at dusk without MCR Safety’s new photochromic lens!
Ride in style and with protected photochromic glasses.
Transition glasses may or may not be right for you, but they’re an excellent example of how safety glasses continue to evolve as new technology is introduced.
Needs in the Workplace
Yes, we do love ensuring bikers have the right glasses, however, the primary purpose of these glasses is to keep your eyes safe in industrial environments. By wearing photochromic lenses, workers can mitigate the risks of working out in the sun. They are especially beneficial if workers are spending long periods in the sun or have to work both indoors and outdoors. As we mentioned above, wearing photochromic lenses negates the need to have two pairs of glasses.
Workers in outdoor occupations, such as construction, oil and gas, and utilities, will be eager to test out our new photochromic safety glasses. Here are a couple of everyday applications where these lenses impact worker experience:
- Construction work: when working inside a structure and then moving to outdoor work. For example, a carpenter that is working on the interior of a new home, then moves outside to obtain materials.
- Service technicians: working on outside equipment, then transitioning to indoors. For example, an HVAC worker servicing HVAC equipment on a roof, then going indoors.
Photochromic Style w/ Max 6 Technology
In a 2013 survey conducted at MCR Safety tradeshow events, 59% of respondents noted Anti-Fog as the most important buying factor. At MCR Safety, we know users value this technology, so we’ve added our Max 6 Anti-Fog coating to our new auto-tinting safety glass.
We didn’t stop there, though. We’ve incorporated a comfortable TPR nosepiece and a 3-point ratcheting hybrid temple. Plus, our photochromic safety glasses comes with its very own case. Check out both the glass and case below.
MCR Safety's VL220PCPF
Protecting Eyes in Transition
When choosing a pair of auto-tinting safety glasses, it’s important to know how long the transition will take, as well as the level of VLT offered by each pair. By reading the above, we hope you know more about the technology, how it works and why.
For over 45 years, MCR Safety has proven to be a world-leader in gloves, glasses, and garments. Whether it’s on the shop floor, an oil rig, or a construction site, we are there providing solutions to workplace hazards. It’s all part of our commitment to protect people. No matter your industry, we have the personal protection equipment you need.
We Protect People, especially when transitioning from clear to dark environments!
Learn more about MCR Safety by checking out our most recent video. For more information, browse our website, request a catalog, find a distributor, or give us a call at 800-955-6887.