FAA Brochure - Sunglasses for Pilots

Sunglasses

for Pilots:

OK-24-1154 9/18/2024enhancing contrast in hazy conditions. Yellow,

amber, and orange (i.e., “Blue Blockers”) tints

eliminate short-wavelength light from reaching

the wearer’s eyes and reportedly sharpen vision,

although no scientific studies support this claim.3

In addition, these tints are known to distort colors,

making it difficult to distinguish the color of

navigation lights, signals, or color-coded maps

and instrument displays. For flying, sunglass

lenses should screen out only 70 - 85% of visible

light and not appreciably distort color. Tints that

block more than 85% of visible light are not

recommended for flying due to the possibility of

reduced visual acuity, resulting in difficulty seeing

instruments and written material inside

the cockpit.

Since sunglasses are an important asset, whether

or not refractive correction is required, careful

consideration should be used when selecting an

appropriate pair for flying.

Finally, the technology associated with ophthalmic

lenses is continually evolving, with the introduction

of new materials, designs, and manufacturing

techniques.

Aviators should consult with their eyecare

practitioner for the most effective alternatives

currently available when choosing a new pair of

sunglasses. frames of an aviator’s sunglasses,

however, must be functional and not interfere with

communication headsets or protective breathing

equipment. Frame styles that incorporate small

POLARIZATION

Polarized lenses are not recommended for use

in the aviation environment. While useful for

blocking reflected light from horizontal surfaces

such as water or snow, polarization can reduce

or eliminate the visibility of instruments that

incorporate anti-glare filters. Polarized lenses

may also interfere with visibility through an

aircraft windscreen by enhancing striations in

laminated materials and mask the sparkle of light

that reflects off shiny surfaces such as another aircraft’s wing or windscreen, which can reduce the

time a pilot has to react in a “see-and-avoid” traffic

situation.

Polarized sunglasses are not recommended

because of their possible interaction with displays or

other materials in the cockpit environment.

PHOTOCHROMIC

Glass photochromic lenses (PhotoGray® and

PhotoBrown®), like their plastic counterparts

(Transitions@). automatically darken when exposed

to UV and become lighter in dim light. Most of the

darkening takes place in the first 60 seconds, who

lightening may take several minutes. Although most

photochromic lenses can get as dark as regular

sunglasses, i.e., 20% light transmittance in direct

sunlight, warm temperatures (>700F) can seriously

limit their ability to darken, and reduced UV exposure

in a cockpit can further limit their effectiveness.

In addition, the faded state of photochromic glass

lenses may not be clear enough to be useful when

flying in cloud cover or at night.

FRAMES

The selection of sunglass frames is probably more

a matter of personal preference than lens material

or tint. The frames of an aviator’s sunglasses,

however, must be functional and not interfere with

communication headsets or protective breathing

equipment. Frame styles that incorporate small

lenses may not be practical, since they allow too

much visible light and UV radiation to pass around

the edges of the frame. A sunglass frame should be

sturdy enough to take some abuse without

breaking, yet light enough to be comfortable. An

aviator’s sunglasses should fit well so that sudden

head movements from turbulence or aerobatic

maneuvers do not displace them. Finally, use of

a strap is recommended to prevent prescription

sunglasses from being accidentally dislodged, or

a necklace chain can be used to allow them to be

briefly removed and subsequently replaced.REFERENCES

1. La Comission Internationale de l’Eclairage (CIE).

Figures correspond broadly to the effects of UVR

on biological tissue.

2. World Meteorological Organization.

Scientific Assessment of Ozone Depletion: 1994,

WMO Global Ozone Research and Monitoring

Project - Report No. 37, Geneva, Switzerland:1995.

3. Rash CE, Manning SD. For Pilots, Sunglasses are

Essential in Vision Protection. Flight Safety Foundation

Human Factors & Aviation Medicine, July-August

2002; 49(4): 1-8.

• Protecting a pilots most

important sensory asset

• Radiation

• Lens Material

• Tints

• Polarization

• Frames

BEFORE YOU FLY

1. Neutral gray tint is highly recommended

2. Photochromic lenses are not recommended

3. Polarized lenses are not recommended

Provided by

Aerospace Medical Education Division, AAM-400

To obtain copies of this brochure online:

https://www.faa.gov/pilots/safety/

pilotsafetybrochures/

or contact:

Federal Aviation Administration

Civil Aerospace Medical Institute

AAM-400

P.O. Box 25082

Oklahoma City, OK 73125

(405) 954-4831

Sunglasses help safeguard a pilot’s most important

sensory asset – vision. A quality pair of sunglasses

is essential n the cockpit environment to optimize

visual performance. Sunglasses reduce the effects

of harsh sunlight, decrease eye fatigue, and protect

ocular tissues from exposure to harmful solar radiation.

Additionally, they protect the pilot’s eyes from impact

with objects (i.e., flying debris from a bird strike, sudden

decompression, or aerobatic maneuvers). Sunglasses can

also aid the dark adaptation process, which is delayed by

prolonged exposure to bright sunlight.

RADIATION

RADIATION. Radiation from the sun can damage skin

and eyes when exposure is excessive or too intense.

Fortunately, the Earth’s atmosphere shelters us from the

more hazardous solar radiation (i.e., gamma and X-ray);

however, both infrared (IR) and ultraviolet(UV) radiation

are present in our environment in varying amounts.

This is dependent upon factors such as the time of

day and year, latitude,altitude, weather conditions, and

the reflectivity of surrounding surfaces. For example,

exposure to UV radiation increases by approximately

5percent for every 1,000 feet of altitude.

Atmospheric IR energy consists of long-wavelength

radiation (780 – 1400 nanometers [nm], see Figure 1).

The warmth felt from the sun is provided by IR radiation

and is thought to be harmless to the skin and eyes at

normal atmospheric exposure levels. More hazardous

to human tissues is short-wavelength UV radiation. UV

is divided into three bandwidths: UVA (400 – 315 nm), UVB (315 – 280 nm), and UVC (< 280 nm).1 Excessive

or chronic exposure to UVA and, to a greater extent, UVB

can cause sunburn, skin cancers, and is implicated in the

formation of cataracts, macular degeneration, and other

eye maladies.

The American Optometric Association recommends

wearing sunglasses that incorporate 99 – 100% UVA

and UVB protection. Fortunately, UVC, the most harmful

form of UV radiation, is absorbed by the atmosphere’s

ozone layer before it reaches the Earth’s surface.

Some scientists believe, however, that depletion of the

ozone layer may allow more UV to pass through the

atmosphere,2 making 100% UV protection a wise choice

when selecting eyewear.

LENS MATERIAL

The three most common lens materials in use today are

optical quality “crown” glass, monomer plastic (CR-39®),

and polycarbonate plastic (see Table 1). Lenses made

from crown glass provide excellent optical properties (as

indicated by the high Abbe value). Crown glass is more

scratch resistant but heavier and less impact resistant

than plastic. Glass absorbs some UV light; however,

absorption is improved by adding certain chemicals

during the manufacturing process or by applying a

special coating. Glass retains tints best over time, but

for higher refractive correction, the color may be less

uniform, as parts of the lens will be thicker than others

(see Figure 2). CR-39® plastic lenses possess excellent optical

qualities, are lighter in weight, and more impact

resistant than glass lenses, but are more easily

scratched, even when scratch-resistant coatings

(SRC) are applied. CR-39® lenses tint easily and

uniformly, even for those requiring a great deal of

refractive correction, but do not hold tints as well as

glass. CR-39® plastic can be bleached and re-tinted

if fading becomes excessive at some point.

Polycarbonate plastic lenses are lighter than

CR-39® and the most impact-resistant lenses

available. Polycarbonates have a low Abbe value,

indicating their inherent optical aberrations. The

application of an anti-reflective (AR) coat can

improve optical quality, particularly when a high

refractive correction is required. These lenses have

built-in UV protection and are manufactured with

a scratch-resistant coating that is much stronger than that applied to CR-39® lenses. Since

polycarbonate lenses do not accept dye as readily

as CR-39® plastic, they are less adaptable for use

as sunglasses. However, the interior anti-scratch

coating will absorb tints. High-index materials

(i.e., index of refraction ≥ 1.60) are available in

both glass and plastic for those who require a

large degree of refractive correction and/or desire

lighter, thinner lenses. High-index materials

are not as widely available, require AR coats to

improve optical clarity, and a SRC for durability. In

addition, most high-index materials do not accept

tints as easily and are less shatter resistant than

low-index materials.

COATINGS

Special coatings can be applied to lens materials

for reasons such as those previously mentioned.

Crown glass and most plastic lenses require a

specific coating to block residual UV radiation.

Plastic and polycarbonate lenses require a SRC

to prolong their useful life. The SRC applied to

polycarbonate lenses absorb tints and dyes.

High-index materials benefit from AR coatings to

improve transmissivity due to their high reflective

properties. While AR coats can improve optical

clarity, they are extremely porous, attracting water

and oils, making the lenses difficult to clean.

Lenses with AR coatings should be “sealed” with

a smudge- and water repellent coat that extends

the useful life of the AR coat and make the lenses

easier to keep clean. Coatings must be applied

correctly and lenses must be meticulously cleaned

for the process to be successful. Coated lenses

should be handled with care and not subjected to

excessive heat to avoid delamination or crazing.

TINTS

The choice of tints for sunglasses is practically

infinite. The three most common tints are gray,

gray-green, and brown, any of which would be

an excellent choice for the aviator. Gray (neutral

density filter) is recommended because it distorts

color the least. Some pilots, however, report that

gray-green and brown tints enhance vividness

and minimize scattered (blue and violet) light, thus

Figure 1. Electromagnetic radiation spectrum including visible, infrared, UVA,

UVB, and UVC wavelengths

Table 1. Properties of the three most common lens materialsFigure 2. Illustration of non-uniform tints with glass lenses for high

hyperopic (left) and myopic (right) corrections