Window Tint Guide: Understand
Car Windows, UVA and Your Eyes
Eye doctors have long wondered why cataracts and skin damage around the eyes seem to show up more on one side of the face. In countries where people drive on the right side of the road, the left side faces the driver's window for every mile.
A 2016 study measured how much UVA actually gets through car glass. The answer helps explain where window film can help your eyes, where sunglasses still matter, and why darker is not always better for seeing.
The short answer
Car windshields block most UVA, but side windows let through much more, and the amount varies widely by car. A 2016 JAMA Ophthalmology study found windshields blocked 96% of UVA on average versus 71% for driver's side windows. The author suggested this may help explain reported higher rates of left-eye cataract. UV-blocking film on side windows closes most of that gap; sunglasses with full UV protection remain important.
Key points
- Windshields averaged 96% UVA blocking in the study; driver's side windows averaged 71%, ranging from 44% to 96%.
- A link between driving and left-eye cataracts is a plausible hypothesis, not a proven cause.
- Time in the sun is a recognized cataract risk factor; eye doctors recommend sunglasses with 100% UV or UV400 protection.
- UV-blocking window film works regardless of shade, so eye protection does not require dark tint.
- Tint reduces daytime glare but also reduces light at night, which matters more as eyes age.
The study
What the JAMA Ophthalmology study measured
Published in JAMA Ophthalmology in 2016, the study measured UVA outside 29 cars from 15 manufacturers, then behind each car's front windshield and behind the driver's side window. The cars ranged from 1990 to 2014 model years and were at dealerships in Los Angeles.
Windshields were consistent: they blocked an average of 96% of UVA, in a narrow range of 95% to 98%. Side windows were lower and highly variable, averaging 71%, with a range from 44% to 96%. Only 4 of the 29 cars, about 14%, had side windows blocking more than 90% of UVA.
The author's conclusion was cautious. The results may in part explain reported higher rates of cataract in left eyes and left-sided facial skin cancer, and automakers may wish to consider more UVA protection in side windows.
Cataracts
UV, time in the sun and cataracts
A cataract is a clouding of the eye's natural lens. The National Eye Institute lists having spent a lot of time in the sun among the factors that raise cataract risk, and notes that more than half of all Americans age 80 or older either have cataracts or have had surgery to remove them. Age remains the biggest factor.
The American Optometric Association, summarizing the study, noted that experts have long suspected sun exposure through the driver's side window adds to the accumulated UV behind a pattern of more cataracts and skin cancers on the left side of the face in North America, the reverse of what is seen where people drive on the other side of the road.
It is important not to overstate this. The study measured glass, not eyes, and it did not show that driving causes cataracts. What it does show is that the driver's window is a real and variable source of UVA, and one you can control.
Two layers
Window film and sunglasses do different jobs
- Window filmProtects everyone, every trip
- LLumar rates its films to block up to 99% of UV rays, and its spec sheet lists greater than 99% UV protection for clear and dark films alike. Film works whether or not anyone remembers sunglasses, and it covers passengers and children too. UV and skin
- SunglassesProtect your eyes everywhere
- The American Academy of Ophthalmology recommends sunglasses with 100% UV or UV400 protection, or that block both UVA and UVB. They protect you outside the car and through the windshield's visible glare, which film below the AS1 line cannot address in South Carolina.
- Hat with a brimSimple and effective
- The National Eye Institute suggests sunglasses and a brimmed hat to block the sun. Useful for time outdoors, less so behind the wheel.
Glare
Glare: where tint helps your eyes in a different way
Glare is not a UV problem; it is too much visible light. Squinting into a low sun on an eastbound morning commute, or catching reflections off wet pavement and other cars, is tiring and can make it harder to see. Tinted side and rear windows reduce the visible light coming from those directions. LLumar's published data lists calculated glare reduction figures for each film, rising as the film gets darker.
The windshield is where most driving glare comes from, and South Carolina allows film only above the AS1 line. A legal sun strip along the top helps when the sun is high enough to sit behind it. For low sun straight ahead, the visor and good sunglasses do the work.
If glare is your main concern, think about which direction it comes from on your regular routes. Side window glare on a long north-south drive is something tint fixes; glare through the windshield on a sunrise drive is not.
At night
The trade-off after dark
The same property that cuts daytime glare reduces the light reaching your eyes at night. Darker side and rear windows make mirrors, blind-spot checks and backing up in a dark parking lot harder, and many people find dim conditions harder to see in as they get older.
South Carolina's 27% combined minimum on regulated windows puts a floor under this, but within the legal range there is still a big difference between a light and a dark film. If you do a lot of night driving or already notice that dim roads are harder to read, choose a lighter shade. A light ceramic film can still block UV and reduce heat.
Medical needs
If your eyes are sensitive to light
Some medical conditions make people unusually sensitive to light. South Carolina's statute includes an exemption for a vehicle registered to a person, or their legal guardian, who has an affidavit signed by a physician or an optometrist licensed in South Carolina stating that a physical condition makes darker or more reflective film necessary. The affidavit must be kept in the vehicle, shown to an officer on request and updated every two years.
Notice that an optometrist can sign it, not only a physician. If light sensitivity is affecting your driving, raise it at your next eye exam; your eye doctor can tell you whether a medical exemption makes sense or whether a lighter film plus prescription sunglasses is the better answer.
This is general information, not medical or legal advice.
Practical
Protecting your eyes on the road
Add UV-blocking film to the side windows
Start with the driver's window, where the study found protection weakest and most variable.
Choose the shade for night vision as well as looks
UV protection does not need dark film. Go lighter if you drive a lot after dark.
Keep good sunglasses in the car
Look for 100% UV or UV400 protection for windshield glare and time outside.
Keep glass clean inside and out
Haze on the inside of the windshield scatters light and makes glare and night driving worse.
Keep up with eye exams
Mention it to your eye doctor if glare or night driving is getting harder.
UV protection on the glass you look through
LLumar rates its films to block up to 99% of UV rays. We offer LLumar Carbon and LLumar Ceramic and check the legal shade for your vehicle before installing. Medical exemption? Bring the paperwork and ask before you book.
Common questions
Do car windows protect your eyes from UV?
The windshield does a good job: in the 2016 JAMA Ophthalmology study, windshields blocked about 96% of UVA on average. Side windows are much less consistent, averaging 71% and as low as 44%. So your eyes are well protected looking forward but less so from the side, which is why UV-blocking film on side windows and UV-rated sunglasses are both useful.
Can driving cause cataracts in the left eye?
It has been suggested but not proven. Experts have noted more cataracts and skin cancers on the left side of the face in countries where drivers sit on the left, and the 2016 study found driver's side windows let through considerably more UVA than windshields. That makes driving exposure a plausible contributor, alongside age and overall time in the sun, but no study has shown it causes cataracts.
Do I still need sunglasses if my windows are tinted?
Yes, for most people. Film on the side windows blocks UV from the side, but South Carolina does not allow film on the windshield below the AS1 line, so glare and light from straight ahead still come through. Sunglasses with 100% UV or UV400 protection also protect you outside the car.
Is dark tint bad for your eyes at night?
Dark tint does not harm your eyes, but it does reduce the light you have to see with after dark. That makes mirrors, side views and backing up harder, especially for drivers who already find dim roads hard to read. If night driving is a concern, choose a lighter legal shade; you can still get UV protection and heat rejection from a light ceramic film.
Keep reading
Sources
- Boxer Wachler BS, Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows, JAMA Ophthalmology 2016;134(7):772-775, PubMed (https://pubmed.ncbi.nlm.nih.gov/27258091/), accessed October 2026
- Correlation: Cataracts and UV exposure in driver-side windows, American Optometric Association (https://aoa.org/news/clinical-eye-care/correlation-cataracts-and-uv-exposure-in-driver-side-windowsdiabetes-and-diabetes-related-eye-disease), accessed October 2026
- Cataracts, National Eye Institute (https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts), accessed October 2026
- The Sun, UV Light and Your Eyes, American Academy of Ophthalmology (https://www.aao.org/eye-health/tips-prevention/sun), accessed October 2026
- LLumar Window Film Performance Data (LL0116NAEN), Eastman Performance Films (https://www.llumar.com/content/dam/eastman/performance-films/llumar/documents/LL0116NAEN_AutoSpecs_screen.pdf), accessed October 2026
- S.C. Code Ann. § 56-5-5015, South Carolina Legislature (https://www.scstatehouse.gov/code/t56c005.php), accessed October 2026
Prices on this page are The Auto Show’s published starting prices. Film ratings and warranty terms come from the manufacturer. This guide explains South Carolina law in plain words; it is not legal advice.