Polarized sunglasses are generally beneficial for vision and are not harmful to the eyes. They function specifically to reduce discomfort caused by reflected light, known as glare. Confusion about their suitability arises from specific situations where their glare-reducing mechanism interferes with certain visual tasks or modern technology.
Understanding Glare Reduction
Light from the sun vibrates in all directions, but when it reflects off a flat, smooth surface like water, a wet road, or snow, it becomes concentrated. This reflected light vibrates predominantly along the horizontal plane, creating intense glare. Polarized lenses are manufactured with a chemical film featuring long-chain molecules aligned vertically. This vertical alignment acts like a set of vertical blinds, allowing only light waves that vibrate vertically to pass through to the eye.
The filter effectively blocks the horizontal light waves that cause glare while transmitting the remaining vertical waves. By selectively absorbing the horizontally polarized light, these lenses reduce eye strain and improve visual contrast near reflective surfaces. This process allows wearers to see below the surface of water or observe objects on a road without distracting reflection. The selective light transmission results in a clearer image, making outdoor activities like driving and fishing more comfortable.
The Critical Distinction: Polarization and UV Protection
The function of polarization is entirely separate from the function of ultraviolet (UV) protection. Polarization addresses visible light, specifically the glare that causes discomfort. UV protection addresses invisible electromagnetic radiation, including the harmful UVA and UVB rays that can damage eye tissues over time.
UV radiation increases the risk of developing serious eye conditions, such as cataracts and macular degeneration. A lens can be fully polarized without offering UV protection, and a lens can provide 100% UV protection without being polarized. Therefore, ensuring they block 99% to 100% of both UVA and UVB rays is the primary concern for long-term eye health. Polarization is a feature for visual comfort, while UV protection is a requirement for ocular safety.
When Polarization Becomes a Visual Obstacle
The same filtering mechanism that eliminates glare can create visual problems when interacting with modern technology and specific environments. Many digital displays, including Liquid Crystal Displays (LCDs) used in smartphones, car navigation systems, and cockpit instruments, emit light that is already polarized. When the lens’s polarization angle aligns perpendicularly with the screen’s angle, the filters cancel each other out, causing the display to appear dark or black. Tilting the head can sometimes restore visibility by changing the lens angle relative to the screen’s polarization.
This interference makes polarized lenses unsuitable for certain occupations where viewing these screens is necessary for safety. Aviation authorities, such as the FAA, do not recommend polarized sunglasses for pilots because they can obscure LCD cockpit instruments and interfere with anti-glare filters on windscreens. Polarization can also mask visual cues important for safety in certain outdoor activities. For example, polarized lenses may reduce the ability of boaters to spot subtle reflections off ice patches or the sparkle of light reflecting off another aircraft. The lenses may also make it harder for drivers to detect patches of black ice or subtle changes in road surface texture revealed by reflected light.