When looking through polarized sunglasses, some people notice unusual visual effects, such as wavy patterns or colorful, rainbow-like displays, particularly when viewing certain surfaces. This phenomenon can appear on car windows, phone screens, or even some building glass. This visual experience is not a flaw in the eyewear or a sign of vision problems but rather an interaction between the polarized lenses and specific materials.
How Polarized Lenses Work
Polarized lenses are designed to reduce glare by filtering light waves. Light naturally vibrates in all directions, but when it reflects off flat surfaces like water or roads, it becomes horizontally polarized. This horizontal light is perceived as glare, reducing visibility.
Polarized sunglasses contain a special chemical filter, often a laminate, with molecules precisely aligned in a vertical pattern. This vertical alignment acts like a microscopic Venetian blind, allowing only vertically vibrating light waves to pass through while blocking the horizontally oriented light that causes glare. These lenses enhance visual comfort and clarity by eliminating harsh reflections.
The Science Behind the Colors
The appearance of colors or wavy patterns when wearing polarized sunglasses is due to an optical phenomenon known as stress birefringence, also referred to as photoelasticity. Many transparent materials, including glass and some plastics, are subjected to mechanical stress during their manufacturing process or subsequent use. This stress can create internal variations in the material’s molecular structure.
When light passes through a stressed material, the light waves are affected differently depending on their polarization direction relative to the stress. This causes the light to split into two components that travel at different speeds, effectively altering the light’s polarization state. When this light then reaches the polarized sunglasses, which act as a second polarizer, it creates an interference pattern. Different wavelengths, or colors, of light are either constructively or destructively interfered with, resulting in the visible spectrum of colors. The “rainbows” are not inherent to the sunglasses but rather reveal the internal stress patterns within the other material being viewed.
Where You Might See the Effect
The rainbow effect is commonly observed in several scenarios. Car windows, particularly tempered side and rear windows, are frequent sites for these patterns, as the tempering process introduces internal stresses. Windshields, which are typically laminated glass, show this effect less often.
Liquid crystal displays (LCDs) on devices like smartphones, tablets, computer monitors, and gas pump screens, are also prone to displaying these colors. LCDs inherently manipulate polarized light to create images, and their interaction with polarized sunglasses reveals their internal structure or stresses. Certain plastic objects, such as food containers or protective screens, and glass tabletops can also exhibit these colorful patterns.
Is the Rainbow Effect Normal?
Observing these colorful patterns through polarized sunglasses is normal and expected. It is a direct consequence of the lenses’ ability to filter light interacting with the optical properties of other materials. The effect is a demonstration of fundamental physics, not a defect in the sunglasses or a vision problem.
The presence of these patterns confirms that the polarized lenses are functioning as intended, revealing stress in transparent materials. This side effect does not diminish the effectiveness of polarized sunglasses in reducing glare and enhancing visual clarity. The benefits of glare reduction for activities like driving or water sports outweigh this occasional visual phenomenon.