United States government regulations require automobile windshields to be made with laminated glass to lessen potential injury when shattered. The combination of laminated glass and extra-thick glass in front windshields provides protection against ultraviolet-A radiation.
However, new research from California indicates that automobile side windows do not provide the same level of protection against ultraviolet-A radiation compared to the front-facing windshield, which may increase the risk of cataracts and skin cancer for frequent drivers. In addition, there is increasing evidence that related “blue light” is harmful to the eye and can amplify damage to retinal cells, in eye diseases such as macular degeneration.
From JAMA Ophthalmology
This new automobile and ultraviolet light research, entitled Assessment of Levels of Ultraviolet A Light Protection in Automobile Windshields and Side Windows, has been published “online first” in the May 12, 2016 edition of JAMA Ophthalmology (formerly Archives of Ophthalmology). JAMA Ophthalmology is an international peer-reviewed journal published monthly by the American Medical Association. The study author is Brian S. Boxer Wachler, MD, from the Boxer Wachler Vision Institute, Los Angeles, California.
About the Research
It is a long-known fact that prolonged exposure to ultraviolet A (UV-A) rays can raise the risk for skin cancer and cataracts. For the first time, a research team has indicated that side windows of the car don’t offer enough protection from harmful sun rays.
A recent JAMA Ophthalmology study assessed the protection provided by front windshields and side windows of automobiles from ultraviolet A (UV-A) rays. The study found that protection was consistently high in the front windshields while it was lower and highly variable in side windows. Scientists say that the study findings may to some extent explain the reported increased rates of cataract in left eyes and left-sided facial skin cancer.
For the study, the outside ambient UV-A radiation along with UV-A radiation behind the front windshield and behind the driver’s side window was measured in 29 automobiles from 15 manufacturers. The years of the automobiles ranged from 1990 to 2014, with an average of 2010. [The study] found that the average percentage of front-windshield UV-A blockage was 96%, higher than the average 71% of side-window blockage. A high level of side-window UV-A blockage (more than 90%) was found in four of 29 automobiles (14%).
“Automakers may wish to consider increasing the degree of UV-A protection in the side windows of automobiles. This could contribute to a higher prevalence of left eye cataracts and skin cancer on the left side of people’s faces. Based on the new data, automakers may wish to consider increasing the degree of UV-A protection in the side windows of automobiles,” says [study author] Dr. Brian Wachler.
Visible Light and Light Rays
When discussing sunlight and its damaging effects, an important factor to consider is the measurement of visible light and light rays, beginning with the definition of a nanometer:
- A nanometer (nm) is the measurement of a wavelength of light.
- One nanometer = 1/1,000,000,000 of a meter, or one-billionth of a meter. It’s very small!
- A wavelength is the distance between two successive wave “crests” (ups) or “troughs” (downs):
Visible light rays range from 400 nm (shorter, higher-energy blue wavelengths, bottom) to 700 nm (longer, lower-energy red wavelengths, top).
Ultraviolet Light and Blue Light
The human visual system is not uniformly sensitive to all light rays, however. The visible light spectrum occupies just one portion of the electromagnetic spectrum:
- Below blue-violet (400 nm and below), is ultraviolet (UV) light.
- Above red (700 nm and above), is infrared (IR) light.
- Neither UV nor IR light is visible to the human eye.
Ultraviolet (UV) light has several components:
- Ultraviolet A, or UVA (320 nm to 400 nm): UVA rays age us and penetrate the skin more deeply than do UVB rays. It is now believed that UVA rays contribute to, and may even initiate the development of, skin cancers. They are also able to penetrate glass, unlike UVB rays.
- Ultraviolet B, or UVB (290 nm to 320 nm): UVB rays burn us and play a key role in the development of skin cancer and photoaging [i.e., skin wrinkling and sun damage].
- Ultraviolet C, or UVC (100 nm to 290 nm): UVC rays are filtered by the atmosphere before they reach us.
Blue light rays (400 nm to 470 nm) are adjacent to the invisible band of UV light rays:
- There is increasing evidence that blue light is harmful to the eye and can amplify damage to retinal cells.
- A 2014 study from the National Eye Institute (a) confirmed that sunlight can increase the risk of cataracts and (b) established a link between ultraviolet (UV) rays and oxidative stress, the harmful chemical reactions that occur when cells consume oxygen and other fuels to produce energy.
- UV and blue light are still present even when it is cloudy or overcast.
Absorptive Sunglasses, UV Light, and Blue Light
Absorptive sunglasses help filter out bothersome glare and harmful light rays. Most sunglasses now block out ultraviolet light. However, to block out “blue” light, which causes concern for macular degeneration and other eye conditions, sunglasses need to have some amount of yellow in them.
The colors of sunglasses that contain some yellow and block out blue light are: amber, orange, amber/orange combination, plum, and yellow. Grey and green-grey colored sunglasses do not block out any blue light. Grey and green-grey sunglasses also do not provide contrast as well as do amber, orange, plum, and yellow.
Some advantages of absorptive sunglasses are:
- They can reduce glare, enhance or clarify vision in the sunlight, ease eye fatigue, and protect the eyes from injuries.
- They block out harmful light rays. Most block out ultraviolet (UV) light, while amber, orange, plum, and yellow-colored sunglasses also block out blue light.
- Amber, orange, plum, and yellow-colored sunglasses also help enhance or increase contrast.
- Yellow-colored sunglasses are helpful for use indoors (reading, writing, doing handicrafts, using a computer) to reduce glare and enhance contrast.
- They are generally inexpensive and easy to obtain.
- They can be fitted over regular glasses, and they are available in clip-on or insert styles.
- Please note: Clip-ons and inserts are usually not as effective as fit-over or wrap-around styles, since they do not block light from the top and sides.
- It is recommended that you try on a range of colors and styles during the low vision examination to determine which color or colors work best for you.
You can learn more about absorptive sunglasses at Helpful Non-Optical Devices for Low Vision and Helpful Products and Technology for Living with Vision Loss.
More about the Study from JAMA Ophthalmology
Edited and excerpted from the study abstract:
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 [i.e., at one specific point in time], 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% and was higher than the average percentage of side-window blockage, which was 71%. The difference between these average percentages is 25%. A high level of side-window UV-A blockage (more than 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.
What You Can Do to Protect Yourself
- Always wear sunglasses outside, and make sure they offer protection from UVA, UVB, and blue light.
- Wear fit-over or wrap-around sunglass styles, since they block harmful light from the top and sides.
- Be aware that UV and blue light are still present even when it is cloudy or overcast.
- Wear a minimum of SPF 15 sunscreen outdoors and when driving.
- Investigate UV-blocking window tints or tinted window film for your automobile. Before you invest in this option, however, it is important to determine if these tints are legal in your specific area.