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Original Investigation |

Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows

Brian S. Boxer Wachler, MD1
[+] Author Affiliations
1Boxer Wachler Vision Institute, Beverly Hills, California
JAMA Ophthalmol. 2016;134(7):772-775. doi:10.1001/jamaophthalmol.2016.1139.
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Published online

Importance  Ultraviolet A (UV-A) light is associated with the risks of cataract and skin cancer.

Objective  To assess the level of UV-A light protection in the front windshields and side windows of automobiles.

Design  In this cross-sectional study, 29 automobiles from 15 automobile manufacturers were analyzed. The outside ambient UV-A radiation, along with UV-A radiation behind the front windshield and behind the driver’s side window of all automobiles, was measured. The years of the automobiles ranged from 1990 to 2014, with an average year of 2010. The automobile dealerships were located in Los Angeles, California.

Main Outcomes and Measures  Amount of UV-A blockage from windshields and side windows. The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98% [95% CI, 95.7%-96.3%]) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96% [95% CI, 66.4%-75.6%]). The difference between these average percentages is 25% (95% CI, 21%-30% [P < .001]). A high level of side-window UV-A blockage (>90%) was found in 4 of 29 automobiles (13.8%).

Conclusions and Relevance  The level of front-windshield UV-A protection was consistently high among automobiles. The level of side-window UV-A protection was lower and highly variable. These results may in part explain the reported increased rates of cataract in left eyes and left-sided facial skin cancer. Automakers may wish to consider increasing the degree of UV-A protection in the side windows of automobiles.

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Distribution of Percentages of Front-Windshield UV-A Blockage and of Side-Window UV-A Blockage for the Same Vehicles

The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98% [95% CI, 95.7%-96.3%]) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96% [95% CI, 66.4%-75.6%]) (P < .001). The percentages of UV-A blockage for each automobile’s front windshield and driver’s side window were calculated by subtracting the UV-A energy measured behind the window from the outside UV-A energy. That figure was divided by the amount of outside UV-A energy. This fraction was converted to a percentage by multiplying by 100.

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UV A and B Autoglass Penetration
Posted on May 25, 2016
Rahmin A. Rabenou, M.D., Austin Cope, MD, MBA
Department of Medicine, Southern Arizona VA Healthcare System
Conflict of Interest: None provided


The author states that the level of UV A auto glass protection for drivers is unknown. At least for Honda (and likely the other major manufacturers) this is not entirely accurate. We have spoken to Honda Customer service. The 2015 Honda Accord side window and windshield both block 46% of UV. This is very different from the values in this paper listing 97% and 98% UV A blockage for 2012 and 2013 models. I doubt the level of protection has dropped 50% in 2 years. This paper lists a much higher level of protection which could lead care providers to falsely reassure patients that they are adequately UV A protected in their vehicles.

The author's assumption that UV A and B penetration levels will be similar is not accurate based on UV wavelength and penetration differences. Glass filters out UV B very effectively, but not UV A. Therefore, most car window UV penetration can be assumed to be much higher for UV A which is a longer wavelength than UV B. In order to better understand this, it is important to understand the differences in side window and windshield manufacturing techniques. Side windows are often made of a single layer of tempered glass while the windshield is made of laminated glass with a polyvinyl middle layer for crash protection. The polyvinyl can absorb UV B decreasing penetration.

This paper fails to differentiate factory smoked/tinted from dealer tinted windows. Factory darkened windows lack a protective UV film. This is particularly common in back windows where children often sit. Tints added by the dealer or owner, consists of a darkened film applied over the glass. These film overlays often contain ceramic or metallic particles which are responsible for their UV protective properties. The films are also available as non tinted for UV only protection. These should be considered for the back seat to protect children sitting behind a factory smoked/tinted window. If in compliance with state law, they can also be considered for the windshield where tinting needs to be avoided for driving safety.

When purchasing an automobile, new owners should contact the automobile customer service and ask for the UV specifications. If the car appears tinted, the customer should ask if the tinting is from the original manufacturer, or added later. If original, then consider adding a clear protective UV film. If added later, the dealer will know what type of tint film was used. The amount of UV protection can then be looked up.


Response from Dr. Boxler Wachler:

I would like to thank the commenters for the thoughtful letter regarding my study.  

They write “The author states that the level of UV A auto glass protection for drivers is unknown.  At least for Honda (and likely the other major manufacturers) this is not entirely accurate.”   They also reported a recent phone call with Honda customer service to inquire about the UV protection of a 2015 Honda Accord.   Honda customer service said that car’s side window and windshield block 46% UV.  To validate this information, we also called Honda customer service on two different occasions on June 2, 2016.  During the first call, one representative stated that Honda stopped releasing that information in 2007 and he did not have a reason when asked for one.  During the second call later that day, a different representative instructed us to call the operator and request the marketing department.   We did that and spoke with yet another representative but our call was dropped in the process of transfer.  We called back and still another representative asked if we wanted ‘national marketing’ or ‘regional marketing’.  We said ‘national marketing’ and there was no answer and our call was put back in queue to the operator who sent us to the research and development department who transferred us back to the main Honda switchboard who transferred us to yet another representative who put us on hold for a few minutes came back and told us that Honda abides by all federal and state guidelines and stated that there was no department that would have more detailed information than what he just said.  All together, we were on the phone with Honda for about 30 minutes.  So, our experience of obtaining UV side window and front windshield information from Honda was very different than the commenters.   

Additionally, federal law requires front windshields of all vehicles to have near complete UV-A blockage so the commenters' report that Honda customer service said the windshield blockage is 46% is potentially problematic on two levels:  1) the customer service representative is not reporting correct information or 2) Honda is in violation of federal law for automobile manufacturing of front windshields.

The commenters stated that I assumed UV-A and UV-B penetration levels are similar in my paper.   There was not a single mention in the paper of “UV-B”, so I am not clear regarding the basis for the statement.  They also stated that it is important to understand the differences between windshield and side window construction and then proceeded to explain it.  My paper also discussed these manufacturing differences in the third paragraph of the Discussion section.

The commenters point out that I did not differentiate between factory smoked/tinted windows and dealer tinted windows.   That is correct but I am not sure how it is relevant.  If a driver has a vehicle with a side window tint (regardless of the source of the tint), my study found that one cannot assume the tinted window has full UV-A protection.

In the last paragraph, the commenters advocate for new owners to call their company's customer service to obtain UV information about the windows.  My response is: I hope they have better luck than us.


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