Windshield UV blocks photochromic glasses while driving

photochromic lenses – AAA Northeast’s Car Doctor explains why photochromic eyeglasses can’t darken inside a car: most modern windshields filter ultraviolet light, preventing the lenses from activating. The guidance also comes amid a broader Q&A on vehicle problems, from a 3.7-liter

When a pair of “tint in the sun” eyeglasses turns clear the moment you climb into your car, it can feel like the windshield is ruining your eyes’ best idea. But the problem isn’t your glasses or the dashboard lighting. It’s ultraviolet light.

AAA Northeast’s Car Doctor. John Paul. fielded a reader question about why photochromic lenses—glasses that darken in sunlight—lose their tint after getting into a vehicle. The answer is blunt: photochromic lenses react to ultraviolet (UV) light. Most modern vehicle windshields, because they’re made with laminated construction, filter out a significant amount of UV light. That filtering prevents the lenses from activating, so the tint disappears once you’re behind the wheel.

The windshield design is doing more than just protecting your vision. Paul said windshields are built that way for UV protection. and also because the laminated glass and bonding adhesive contribute to the vehicle’s structural rigidity. roof-crush protection. and airbag support. As for whether there are cars that don’t block UV—Paul said. “As far as I am aware. there are no modern vehicles that do not filter UV light through the windshield.”.

The reader’s follow-up question—why manufacturers can’t address the issue so drivers don’t have to buy sunglasses—lands on a reality Paul ties to the windshield itself: without UV transmission, the lenses can’t be expected to darken.

In the same Car Doctor Q&A, Paul also answered other driver questions that point to a similar theme: what seems like a simple inconvenience often traces back to specific, system-level design or wear.

A reader with a 2009 Jeep Grand Cherokee Laredo equipped with a 3.7-liter V6 described a strange noise that starts fine. drives normally. then after about a 15-minute drive shuts off—and roughly 10 minutes later. restarts with a hammering noise. Paul said a technician would need to listen with a mechanic’s stethoscope to pinpoint the source. He added that a worn rocker arm or lash adjuster is a likely cause based on common issues with the 3.7-liter V6. If the noise has been present for an extended period and left unaddressed. the camshaft may also be damaged and require replacement.

Another reader asked about a 2003 Toyota Corolla with only 70,000 miles where the clock has stopped working. Paul said the clock is a standalone component and is not connected to other vehicle computers. After verifying that relevant fuses are intact and there are no wiring issues. he said the most likely cause is clock failure. A common issue, he said, is a cold solder joint on the circuit board. The options. according to Paul. are to have the circuit board resoldered or replace the clock with a new or used unit.

Fuel additives came up next. A reader asked whether fuel additives break down over time if stored in a sealed. unopened bottle. pointing to an old bottle of Volkswagen Multipurpose Gas Additive (G 001 780 M3) that’s about 7–8 years old and was recommended for a 2012 VW Turbo Beetle. Paul said an engineer from Sta‑Bil indicated Sta‑Bil additives have roughly a five-year shelf life. and that it’s reasonable to assume the Volkswagen additive is similar. He said it likely won’t cause harm if it has remained sealed and appears normal. but its effectiveness may be significantly reduced—“much like expired medication. ” making a fresh bottle the smarter and safer choice.

Odors, too, were on the list. A reader said a car they’d just been given smells terrible—“a mix of an ashtray and a litter box.” Paul said he’s had good results using an ozone generator to remove stubborn odors. noting those devices are commonly used in hotels. He also warned that ozone generators can irritate the throat and lungs of chemically sensitive individuals and may degrade rubber seals if overused. As an alternative. Paul said he recently tried an aerosol odor-eliminating fogger from Mothers Car Care Products. which claims to eliminate up to 99 percent of odors. and he said it worked well in his experience.

Finally, Paul compared car-shopping choices: how the Ford Explorer stacks up against the Toyota Highlander and Kia Telluride. He said the Toyota Highlander has an excellent reputation for long-term reliability and strong resale value. The Kia Telluride, he said, stands out for its upscale, spacious interior and an impressive 10-year/100,000-mile powertrain warranty. He added that historically Ford has trailed Toyota and Kia in reliability. but that the Explorer has improved as of late. offering stronger performance. more engine choices. and advanced technology features. If someone plans to keep a vehicle for three years or less. Paul said the Ford Explorer is a solid choice. For long-term ownership and peace of mind, he said the Toyota Highlander or Kia Telluride may be better. His advice was to test-drive all three, explore the technology, and choose the one that fits needs and preferences.

Paul. an ASE-certified master technician with more than 40 years of experience in the automotive business. signs off by inviting readers to email questions to [email protected] and to listen to the Car Doctor Podcast on Apple Podcasts or other popular podcast sites. For the photochromic glasses question. the takeaway is simple: inside the car. the UV light that would darken your lenses doesn’t reliably reach them—because modern windshields are built to stop it.

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