Have you ever wondered how sunglasses transform a bright, blinding day into a comfortably shaded experience? The science behind sunglasses is both fascinating and essential for protecting our eyes from harmful solar radiation. Let’s delve into the mechanics of how sunglasses work.
In This Article
What do Sunglasses Actually Do?
Let's first understand what sunglasses are designed to do.
Light originates from the sun and can interact with objects in three primary ways: absorption, reflection, and transmission.
Sunglasses employ all three mechanisms to shield our eyes. They predominantly absorb light, slightly transmit it, and, if equipped with a mirror coating, reflect a portion of it as well.
To understand why sunglasses are so effective, consider this: the outdoors can be 100 times brighter than a fully lit indoor room. Our eyes only need a small fraction of this light to maintain excellent vision. So by removing 80-90% of light, sunglasses ensure that just the right amount of light reaches our eyes to see comfortably.
Sunglasses are therefore absorbing and reflecting most of the light in our vision.
How are Sunglasses Made?
Sunglasses utilize specially designed lenses to manage light. The lenses are treated with dyes or tints. In plastic lenses, dyes are embedded in the material, whereas in glass lenses, tints are used.
For plastics, a tint tank is used. the lens is placed in the dye solution to absorb the chemicals. The longer it is in the dye, the darker the tint will be. There is a good (long) video on this here. Watch it at 1.5 speed.
For glass lenses, the actual glass will be made by smelting the other compounds into the mix and will come out of the furnace as tinted lenses. Barberini, who makes glass lenses for many premium brands like Maui Jim, Serengeti, Oliver People's, etc, has a video showing the process.
Essentially, sunglasses are dirty lenses we put in front of our eyes.
There are many chemicals and compounds that are used to manufacture these dyes and tints, and many brands have proprietary blends. Maui Jim, for example, uses rare earth elements as part of their blend to fine-tune the light wavelengths that pass through the lens.
The compounds within these dyes and tints are adept at absorbing or reflecting a significant amount of light—typically around 80-90%. This selective absorption means only 10-20% of light passes through to reach our eyes, allowing us to see comfortably even on the brightest days.
Some brands do this better than others. If the tint isn't evenly applied, saturated enough, uses poor materials, or isn't attached well the sunglasses will not perform or hold up effectively. Sometimes the manufacturing process of even good brands can have mishaps and quality control is key.
Some cheap pairs do not even use dyes. They take a darkened coating and laminate it to the clear lens. This is what you will get from street vendors in shady places. The coating will peel off and it is unlikely that the tint was applied evenly, being stretched out over a lens.
The process continues with adding coatings to the lenses. The coatings can be UV coatings, mirror coatings, hydrophobic (water repellant), oleophobic (oil repellant), anti-reflective (only on the backside of the lens for sunglasses), scratch-resistant, and polarized films.
The coatings are added in different ways. Sometimes they are placed in a vacuum chamber where multiple layers of metal oxides are applied using a process called vacuum deposition. This involves vaporizing the coating material, which then condenses on the lens surface in very thin, uniform layers. UV coatings are often applied using a dip-coating process. The lenses are submerged in a UV-blocking solution and then slowly withdrawn to ensure an even coating.
What happens to the absorbed energy?
When sunglasses absorb light, they also absorb the associated energy. This process converts light into heat, which is why objects left in the sun, including sunglasses, can become warm. However, sunglasses typically don’t get hot enough to cause discomfort when touched. Other objects, like cars and metal surfaces, can become scorching under the sun—they absorb and convert a large amount of solar energy into heat.
How to Use Sunglasses to Change Color Perception
The colors we perceive in objects are a result of light being reflected from their surfaces to our eyes. An object absorbs certain wavelengths of light more than others, reflecting the remaining wavelengths, which determine the color we see. Objects themselves don’t possess color; it’s their interaction with light that creates the hues we observe. This is explained more here.
Sunglasses as Light Filters
Sunglasses allow us to manipulate the light entering our eyes, adjusting brightness and color. By fine-tuning the amount of light transmitted through the lenses, sunglasses can enhance visual comfort and clarity. They can also alter the perceived color of objects by filtering specific wavelengths of light. Reds, greens, and blues can all be fine-tuned to be the most visually pleasing shades and brightness possible.
This capability is akin to how photographers use filters to adjust images, enabling us to experience the world in the most visually appealing and comfortable way possible. Photographers can only do it afterward, with computers. We can do it with the computing power of our brain combined with color-enhancing sunglasses in the moment, and even better.
Have you ever been to a beautiful place and thought "Wow, could anything be better than this?"
With the right pair of sunglasses, it most certainly can.
In essence, sunglasses are more than just a fashion accessory. They are sophisticated tools that manage the light spectrum to protect our eyes and enhance our visual experience. Whether it’s reducing glare, enhancing contrast, or simply making a sunny day more bearable, sunglasses play a crucial role in our daily lives. So next time you put on a pair of shades, you’ll know the science behind their magic!