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2008 FAA windscreen transmittance study


This is a technical report which may be of interest regarding how much infrared light goes through an aircraft windscreen. (We are not aware of studies on visible light.)

Infrared Radiation Transmittance and Pilot Vision through Civilian Aircraft Windscreens, by Van B. Nakagawara, Ronald W. Montgomery, and Wesley J. Marshall, June 2008.

Abstract


Introduction


In support of a Department of Homeland Security project, Civil Aviation Medical Institute researchers measured the optical transmittance properties of aircraft windscreens. This paper focuses on windscreen transmittance in the infrared (IR) spectral region (780 – 4000 nm) of the electromagnetic spectrum.

Methods


Transmission measurements were performed on eight aircraft windscreens. Three windscreens were from large commercial jets (MD 88, Airbus A320, and Boeing 727/737); two from commercial, propeller-driven passenger planes (Fokker 27 and the ATR 42); one from a small private jet (Raytheon Aircraft Corporation Hawker Horizon); and two from small general aviation (GA), single-engine, propeller-driven planes (Beech Bonanza and Cessna 182). The two GA aircraft windscreens were plastic (polycarbonate); the others were multilayer (laminated) composite glass.

Results

The average transmittance for both glass laminate and plastic windscreens in the IR-A region (780 – 1400 nm) varied considerably (47.5% ± 11.7%), with glass windscreens consistently attenuating more IR than plastic windscreens. The average difference in transmittance between the two materials fluctuated (27.3% ± 15.9%) throughout the first half of the IR-B spectrum (1400 – 3000 nm) up to approximately 2200 nm when transmittance dropped below 7%. The average transmittance for glass and plastic windscreens became negligible beyond 2800 nm.

Conclusion


Researchers concluded that aircraft windscreens provide a level of protection from potential ocular and skin hazards due to prolonged or intense exposure to IR radiation. The amount of protection is dependent on the type of windscreen material, the wavelength of the radiation, and angle of incidence. On average, laminated glass windscreens attenuate more IR than plastic. Additional research is recommended to confirm that the measured transmittance values for this sample of windscreens are typical of all aircraft windscreens currently in service and to evaluate the potential threat posed by new applications, such as IR lasers, in navigable airspace.