How Polarized Lenses Work – Protecting Your Eyes

Before we can discuss how polarized lenses work we first need to understand what lenses themselves are, and then how polarization relates to their functioning. For our purposes we need to discuss two types of lenses, the anatomical (human) lens and the physical (glasses) lens.

The reason it is important to understand how polarized lenses work is because they can either be a benefit for the wearer, or alternatively, they could create problems for the wearers. As an example, fishermen really like polarized lenses because they allow them to look past the glare on the water’s surface and see the fish in the water.

On the other hand, being able to see the glare from the sun’s rays reflecting off of the surface of another aircraft is a benefit to pilots, particularly to fighter pilots who rely upon their eyes to see opposing fighter aircraft before the other pilot sees them. This is one reason why pilots prefer Randolph Aviator sunglasses to any others.

How Eyes Work

The human eye has a lens which refracts the light entering the eye so that it can be focused on the retina at the back of the eye. The lens in the human eye is also known as the aquula, or crystalline lens, and is made up mainly of water. This lens has the refractive power of approximately 18 dioptres (the reciprocal of the focal length of the lens measured in meters), or roughly one-third of the eye’s total power.

The lens in your eye changes shape which in turn changes the focal distance of the eye so that it can clearly define objects at various distances. In other words, it allows the human eye to see clearly objects that are both near and far away from the viewer at the same time, allowing a sharp image of the objects of interest to be formed on the eye’s retina. Light from the objects of interest enter the eye perpendicular (or horizontal) to the surface of the earth.

An optical lens, on the other hand, is a device with axial symmetry which transmits and refracts light, and either converges or diverges a beam of light. Most optical lenses are spherical, which means that their two surfaces are parts of the surfaces of a sphere.

Each surface of the lens can be either convex (which bows outwards) or concave (which bows inward), and the line which joins the centers of the two surfaces making up the lens is called the axis of the lens. The axis will typically pass through the physical center of the lens, and therefore light entering the lens is perpendicular, or horizontal, to the surface of the earth.

The important thing to recognize here is that in both natural and optical lenses light enters the lens perpendicular to the surface of the earth, and is therefore horizontal light versus vertical light which would come from above or below the axis of the lens.

Light: An Electromagnetic Wave

Light is actually an electromagnetic wave, and can be represented by a vector (the direction of propagation in the figure below) where the electrical and magnetic fields are perpendicular to each other and to the direction of propagation. These two fields change with time and space in a sinusoidal manner.

In the image above the blue line represents the electric field, the red line represents the magnetic field, and the direction of propagation is the direction of the light wave.

Ordinary, or natural light, is non-polarized, propagated in an arbitrary direction, and holds it precise orientation for too short a period of time to be measured by instrumentation. However, when light is reflected off of an object such as metal or glass, the light becomes linearly polarized, or polarized along the horizontal axis, perpendicular to the surface of the earth.

Polarized Lenses

Polarized lenses have a laminated surface which contains vertical stripes which allows only vertically polarized light to enter the eyes. This means that light which is reflected off of metal, glass or smooth surfaces will not be able to enter the eyes, thereby eliminating glare from the sun’s rays striking those surfaces.

However, polarized lenses do not provide complete protection from glare because if you tilt your head more than 45 degrees from the vertical some of the horizontally polarized light will still pass through the polarized lens and enter your eyes.

Another effect of polarized lenses is that they lose some of their ability to see the contrast between bright and dark areas, making them less useful in certain conditions. For example, when skiing on snow, polarized lenses will make it more difficult for the skier to see the contrast between snow and shadows as they ski.

Fishermen and drivers of cars, on the other hand, find polarized lenses to be more useful because they are dealing with mainly light reflected from horizontal surfaces, eliminating much of the glare from the sun’s rays striking objects along the driver’s path.

For pilots, the opposite is true. Pilots need to be able to see clearly, and the reflection of light from metallic and glass surfaces can help them spot an aircraft on a converging course quicker, allowing them to adjust their flight path to avoid the other airplane.

About The Author

John M. White, publisher of All-Things-Aviation.com, is an ATP pilot and aviation enthusiast. He writes articles providing valuable tips and advice for consumers interested in purchasing products for pilots and aviation aficionados. You can find a great selection of Randolph Engineering sunglasses along with advice on the importance of selecting the best aviator sunglasses for pilots

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