Obtaining the correct knowledge of eyeglasses and lenses, which you do not know unexpectedly, will help you to care for your own eyes and eyesight. Please use it as a reference for living a healthy and comfortable visual life.
Vol.11 Story about polarized lenses
We have introduced color lenses and dimming lenses in "Story of Glasses and Lenses Vol.8 , Vol.9 , Vol.10".
This time, we will talk about "polarized lenses".
Some people think of the word "changing lens" in the sense that the color changes, and some people confuse it with the dimming lens of Vol.10. I'll guide you.
1. What is polarized light?
Light emitted from the sun and lighting equipment travels in various directions. This is called unpolarized or unpolarized.
When the light hits fine particles in the air and is confused (confused light), or when it is reflected by glass or the surface of the water and becomes a regular direction, it is called "polarized light".
In other words, when the light hits something, the direction of travel is determined, and the "light is biased".
A laser beam is a typical practical example of polarized light.
Some 3D used in movie theaters and theme parks also use polarization technology.
The human eye has the function of changing the size of the pupil to adjust the amount of light entering the eye when it is dazzling, but the polarized light reflected by the glass or water surface feels flickering, diffuse reflection, or shine depending on the angle, so natural light. It feels more dazzling than.
2. What is a polarized lens?
It is made by sandwiching a special film called a polarizing film between lenses, or a lens with a function to control polarization as a coating on the lens surface.
The products and colors we handle differ depending on the manufacturer and retailer, but we can make them with or without prescription, and the materials used for the lenses are also different.
Some are made of glass, while others are made of polycarbonate.
The light (polarized light) reflected on the glass surface or water surface is controlled by a filter or coating to reduce glare, and there is almost no difference in the effect with any type of polarized lens.
2-1 Visible light transmittance and degree of polarization
Visible light transmittance and degree of polarization are numerical values that can be compared as differences in the appearance of polarized lenses.
Visible light transmittance is the rate at which light passes, and is expressed as a numerical value from 0 to 100%.
A low transmittance (close to 0%) cuts light, and a high transmittance (close to 100%) allows light to pass through.
In terms of the density of a color lens, the color is darker when the transmittance is close to 0%, and the color is lighter when the transmittance is close to 100%.
The degree of polarization is the ratio of blocking polarized light (reflected light), and is expressed as a numerical value of 0 to 99% like the transmittance, and there is a definition that "a polarized lens with a degree of polarization of 90% or more".
There is an inverse relationship between the visible light transmittance and the degree of polarization. The higher the degree of polarization, the lower the visible light transmittance, and the higher the visible light transmittance, the lower the transmittance.
That balance is important when choosing a polarized lens.
2-2 Polarized lens color
Polarized lenses of various colors are available depending on the lens manufacturer and retailer.
As mentioned in the story of color lenses in Vol.8, please see that for the role of color.
2-3 UV protection for polarized lenses
Of course, you can also take measures against ultraviolet rays with polarized lenses. Most polarized lenses are UV-cut, but as mentioned in the story about UV rays in Vol.9, the life of the lens depends on whether it is UV-cut or a UV-cut material.
2-3 Polarized lens life
Polarized lenses have a limited lifespan.
With polarized lenses made with a polarizing filter in between, color unevenness will be seen from the periphery of the lens in about 2 to 3 years, depending on the usage environment and frequency of use.
This is a state in which the part where the polarizing filter and the lens are adhered has peeled off, and the polarizing function has also deteriorated. The main causes are deformation of the lens due to heat and moisture invading the filter part.
The biggest cause of shortening the life of coated type polarized lenses is scratches on the lens surface.
Regardless of the period of use, the coating will peel off from the scratches on the lens surface due to wiping the lens with sand or dust on it, or hitting it against a hard object, and the polarization function will deteriorate. increase.
If you continue to use it with its polarization function deteriorated, it will affect the appearance, so consider replacing it as soon as possible.
3. Precautions for polarized lenses
Finally, I would like to inform you about the points to note when using polarized lenses.
◎ Please be careful when driving a car.
Please refrain from wearing it when passing through a tunnel or while driving at night or at dusk.
Like most sunglasses, polarized lenses should not be used at night, at dusk or when driving in tunnels. Visual acuity deteriorates due to insufficient light.
According to JIS regulations, lenses with a visible light transmittance (visual transmittance) of less than 75% are prohibited from being used for driving or on the road at dusk or at night, so should a lens with a transmittance of 75% or more be selected? Make sure to use polarized sunglasses with lenses that the manufacturer uses for night driving.
Also, depending on the type of glass in the car, you may even see the distortion of tempered glass. In such a case, the visibility will be poor, so please do not use it.
◎ It may be difficult to see the LCD panel.
If you look at a smartphone, computer, car navigation monitor, etc. while wearing sunglasses with polarized lenses, the screen may become black or difficult to see. This phenomenon occurs because the polarizing plate is also used in the liquid crystal panel and the liquid crystal device itself. The appearance changes depending on the viewing angle, so it is recommended that you check the appearance at the time of purchase.
◎ Be careful not to scratch the lens surface or place where there is a temperature difference.
Coating type polarized lenses lose their polarizing function due to scratches on the lens surface or coating peeling.
Also, if exposed to a sudden temperature difference or high temperature (about 60 ° C or higher), it may cause defects in the coating or polarizing film. Do not place it in a hot car, on a sandy beach, near a heater, or near a fire. Even if you use it in a cold place such as a refrigerator or in the extremely cold winter, it may cause coating defects, so please avoid using it.
◎ Please be careful about washing with water.
If a polarizing lens is created by sandwiching a polarizing film between lenses, if it is left immersed in water or an ultrasonic cleaner, water may seep into the polarizing film, causing discoloration, deterioration, or peeling of the periphery of the lens.
If the lens gets wet, wipe it off immediately and let it dry well.
If you seal the case with water droplets on the frame, the lens may get steamed.
[Personal Sunglasses]
Personal sunglasses
Charmant Namiki St. Ginza, just for you to suit your lifestyle
Want to find "personal sunglasses"?
What is "personal sunglasses"?
These sunglasses allow you to freely combine frames and color lenses carefully selected by the staff.
We will find your favorite combination and hand it to you on the spot.
Of course, it is also possible to make prescription and non-prescription sunglasses by choosing the one you like from all the frames that are always on display at the store.
It may take some time to complete, so please contact the staff for details.
On the left photo:
XL1817 BU + green color lens (visible light transmittance 15%)
Bottom left photo:
XL1819 BR + gray / blue color lens (visible light transmittance 53%)