The Best Sunglasses for Pilots


"Sunglasses are a topic dear to the heart of aviators. There are a number of factors which determine the suitability or otherwise of sunglasses for use in the aviation role. 

Narrow frames that carry large lenses are the most desirable from a field of view standpoint. The most critical problem with frames arises from the presence of wide sidearms which can significantly impair the peripheral visual field.

Lenses should not be too dark, and should transmit at least 15% of incident light. The tint used should be "neutral density" (N.D.), that is, a greyish tint that does not distort colour perception. Much has been written about the perceived benefits of various coloured lenses, especially in regard to contrast and perceived brightness. Coloured lenses have been shown to reduce the colour information received, and to have a detrimental effect on both perception and reaction time. 

Lenses of polycarbonate material are preferred because of their impact-resistance and ability to absorb ultra-violet and infra-red rays. However, these lenses can scratch easily. Harder materials may be suitable, however these may be more prone to shattering in an impact.

Different jurisdictions and countries have standards to which sunglasses are manufactured. Sunglasses should be chosen which conform to the appropriate standard. For example, the current Australian Standard ensures that sunglasses meet acceptable standards for lens quality, frame strength and lens retention and also ensures that sunglasses provide adequate protection from solar radiation. 

Polarising sunglasses should not be used when flying. The polarising filter interacts with the cockpit transparency to produce a distorted and degraded visual image. This effect can also be seen with laminated car windscreens. Better keep the polarised lenses for fishing.

Pilots who wear prescription spectacles can choose from a number of options for glare protection. Prescription sunglasses with N.D.15 lenses can be obtained, or N.D.15 clip-on or flip-up sunglasses may be worn over prescription spectacles.

Back to the original issue of photochromatic lenses. Photochromatic lenses have several disadvantages that render them unsuitable for use by pilots.

Firstly, their transition times are relatively slow. Photochromatic lenses take about five minutes to increase their density to the level of sunglasses, but more importantly, the bleaching time from maximum to minimum density can be as long as 30 minutes. Although there is a rapid lightening of the lens in the first five minutes, this may be too long when there is a sudden variation in light during a descent into or under cloud, or because of a rapid change in cloud cover.

Their second disadvantage is that, even when fully bleached, photochromic lenses still absorb slightly more light than untinted lenses. Since vision is critically dependent on ambient light levels, even this small decrease of light reaching the eye through photochromatic lenses is undesirable, especially at night or in low light levels. The inherent degradation of these lenses with time causes them to progressively become darker, as they become unable to reach the fully bleached state. This effectively prohibits their use in flying or controlling air traffic.