Sunglasses are an important piece of protective equipment in the cockpit environment. Evidence indicates that a proportion of airline cockpit windshields transmit some ultraviolet (UV) radiation. While this radiation is not the higher energy UV which causes sun tanning or sunburn, it can nevertheless result in a significant UV exposure to the eyes during flight. All sunglass filters conforming to national or international regulations will filter eye exposure to any UV inside the cockpit to minimal levels.
The following information offers guidance to pilots purchasing sunglasses.
The tint should be neutral in colour. Grey or brown are acceptable. The tint should be no darker than 80% absorption. A graduated tint (darkest at the top of the lens and lightening towards the bottom) may be useful.
Photochromic lenses normally react with UV radiation to darken. These lenses will not work as effectively in the cockpit environment and do not lighten quick enough in fast changing aviation environments such as descent through cloud. The use of these sunglasses is therefore not encouraged.
Polarised lenses reduce the amount of light passing through the lens by selective filtering of certain electromagnetic spectral planes. These lenses can reduce the conspicuity of some LCD displays and cause distortion patterns from certain multi-layered cockpit windshields. They can also alter cloud appearance and reduce ground reflections useful for pilots operating under visual flight rules (VFR). For these reasons the use of these sunglasses is not encouraged.
All sunglass frames should be well fitting and be large enough to allow sufficient protection from oblique angled sunlight.
All pilots requiring a spectacle prescription must have one clear (untinted) pair of correcting lenses but can have prescription sunglasses as their second pair. The wearing of non-prescription sunglasses on top of prescription glasses is not acceptable.
For night flying, it is recommended that both pairs of prescription glasses are without tint.