Aircraft Windscreen UV: See How You Measure Up

Is your airplane exposing you to an increased risk of skin cancer?

Overview

Pilots are twice as likely to develop skin cancer as the general population, according to a 2015 study by the University of California. Airline crew members are classified as radiation workers by the Center for Disease Control and Prevention, and are subject to more radiation than people who work in nuclear power plants. In addition to an increased risk of skin cancer, ultraviolet (UV) exposure can also lead to eye damage and premature aging.

The amount of UV radiation that a pilot is exposed to varies across different aircraft windscreens. A 2007 study sponsored by the Federal Aviation Administration (FAA) and conducted by the Civil Aerospace Medical Institute (CAMI) evaluated eight windscreens for effectiveness in filtering out UVA light. Aside from this study, there is scant information available as to how windscreens perform.

Method Seven is in the business of designing, producing, and selling eyeglasses to pilots. The company creates exceptional aviator eyeglasses using pristine clear crystal glass lens material that is modified to eliminate harmful ultraviolet energy, to attenuate uncomfortable infrared heat, and to attenuate specific portions of the visible light spectrum to provide contrast. The lenses enhance a pilot’s ability to see well over distance, to maintain natural peripheral vision, to more easily focus, and to recognize contrast when looking towards clouds or towards their instrument panels.

Method Seven Laboratories, the technical arm of Method Seven, embarked on a quest to characterize as many windscreens as possible. To date, M7 Labs has characterized the windscreens on 73 different aircraft. The results are detailed in this report.

Pilot UV Exposure

There are three regions of ultraviolet light - UVC, UVB, or UVA. UVC, with the shortest wavelength (100 – 280 nm), carries the most energy, and is the deadliest of these regions. Fortunately, UVC is completely absorbed by the earth’s ozone layer, and except for certain regions over the poles, never reaches the altitude where aircraft fly. UVB (280 – 315 nm), is also damaging to human tissue, but is largely blocked out by the atmosphere, and is filtered out by almost all glass and plastic windows and screens. UVA (315 – 380 nm), is lower energy and less destructive, but can penetrate more deeply into human tissue. UVA creates cumulative damage and over time can impair the iris and lens of the eyes and damage skin.

As pointed out in the 2007 report, some windscreens do an excellent job of filtering out UVA light - but not all. UVA is a pronounced problem for pilots because the intensity of UVA radiation increases approximately 15% for every 3,000 feet of altitude above sea level. This means a commercial pilot flying at 33,000 feet is flying in a UVA environment that is 4.7 times as intense as experienced at sea level. It is understandable that pilots who fly for long hours during daylight hours wish to know how well their windscreens are filtering out UVA light.

Aircraft Windscreen Evaluation Methods

In the 2007 study, airplane manufacturer’s sent eight windscreens to the (CAMI) Vision Research Laboratory in Oklahoma City, OK. Testing was performed under ideal laboratory conditions using calibrated light sources. In the M7 Labs study, the ambient light spectrum is recorded using a spectrometer in-situ. M7 Labs regularly uses a spectrometer to evaluate how lenses filter light across the ultraviolet, visible, and beginning near infrared portion of the light spectrum. This same tool can be used to evaluate the extent that windscreens filter out ultraviolet light in the UVA region. 

In Figure 1, you see the intensity of light as it varies across different wavelengths, and as captured by a spectrometer. The various regions; ultraviolet-A (UVA), visible (VIS), and near infrared (NIR), are identified. The shape of this spectrum will change depending on whether the sun is overhead or on the horizon and whether the day is clear or cloudy.

Figure 1. Screenshot of sun spectral on a sunny day using a Ocean Optics Flame Spectrometer

In this study, M7 Labs measured the spectrum of light shining towards the aircraft windscreen and then the spectrum of light passing through the windscreen. These two sets of data were used to calculate the ratio of total UVA energy passing through the windscreen divided by the total UVA energy of the sun light shining towards the windscreen. This provided a calculated value for the percentage of UVA that passed through the windscreen.

This method is less precise than the results obtained by CAMI because there can be a change in the intensity of sunlight between the two measurements. Results, however, are sufficiently accurate to clearly demonstrate whether a problem exists, and to identify the approximate magnitude of that problem. Further, this in-situ test technique allowed M7 Labs to measure a larger number of samples than CAMI.

As an example of this technique, Figure 2 shows the intensity of light directed at the windscreen and the intensity of light that passed through the windscreen. It is evident that some light in the UVA range passed through the windscreen. The total energy of each curve was calculated, and approximately 20% of UVA light was found to have passed through the windscreen. Figure 3 shows a windscreen that did not allow any UVA light into the cockpit.

Figure 2. Demonstrates 20% UVA transmission through windscreen.

UV

Figure 3. Demonstrates 0% UVA transmission through windscreen.

UV Exposure at Service Ceiling

Since altitude plays a key role in how much UVA a pilot might be exposed to, the service ceiling of each aircraft was incorporated into testing. For example, the service ceiling for the Embraer EMB-505 aircraft is 45,000 feet. The amount of UVA light present at this altitude is 8 times greater than the amount of UVA light present at sea level.

The Embraer EMB-505 aircraft allows 14% of UVA light to pass through the windscreen at its service ceiling. The effective UVA exposure in an Embraer cockpit, at 45,000 feet, would be 14% times 8.1, or 110% of the exposure a person would experience at sea level.

Results by Airplane and Service Ceiling

Table 1. Tabulation of UVA measurement results, identified by major categories. Out of the 73 aircraft tested, 45 windscreens removed 100% of the UVA light. Seven aircraft, however, allowed 30% or more UVA light to enter through the windscreen.

There was a wide range in service ceilings for the various aircraft that were tested. The highest service ceiling was 51,000 feet and the lowest was 5,000 feet. With such a wide range in likely flight altitudes it was important to factor into the study the effect of the various service ceilings.

Specific data, by aircraft, is provided in Table 2. The last column shows exposure to UVA that a pilot would experience while flying at the service ceiling - referenced to unprotected exposure at sea level. For example, a value of 1.5X indicates a pilot is exposed to 50% more UVA light coming through the windscreen of that particular plane than they would experience sunbathing at the beach.

Table 2. Windscreen Transmittance of UVA vs. Unprotected UVA Exposure At Sea Level

Conclusion

Pilots need to be aware of the amount of exposure to UVA radiation they are experiencing in their respective cockpits. Most aircraft do a proper job of filtering out UVA radiation, but not all. The problem becomes further magnified by the increase in percentage of UVA radiation at higher altitudes.

Most sunglasses do a good job of filtering out UVA - but not all. All Method Seven lenses properly filter out UVA radiation. Further, pilots need to wear protective clothing in the cockpit - and this includes long sleeves. Pilots should also use sunscreen to protect their exposed skin.

Method Seven is available, to work with any pilot union or organization, to measure the amount of UVA radiation entering the cockpit of the aircraft that they fly. For more information, please contact James Cox, CEO at james@methodseven.com.

Respectfully submitted,

Method Seven Labs