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.10 Story about photochromic lens
Sunglasses are very effective as a measure against ultraviolet rays and glare.
However, if you usually wear prescription glasses, you should wear prescription sunglasses.
Even those who spend time with contact lenses or the naked eye will need to carry sunglasses separately.
Therefore, this time, we will talk about "dimming lenses" whose lens color changes with ultraviolet rays and visible light.
1. What is a photochromic lens?
When sunlight or ultraviolet rays hit the lens or the temperature of the lens drops, the color of the lens changes in response.
Molecules (light control materials) that react with sunlight or ultraviolet rays are contained in the lens body and coating, and the color becomes darker when the amount of light hits is large, and the color becomes lighter when the amount is small, which is a fairly chemical mechanism.
Even in this photochromic lens, there are several categories depending on what kind of light rays it reacts to and which part it reacts to.
1-1 UV dimming lens
Lenses that are generally sold as "light control lenses". A lens material or coating that reacts to ultraviolet rays.
The color changes only in response to ultraviolet rays. If the weather is nice outdoors, the color will change deeply (coloring), and if you go indoors, the color will disappear (fading).
Since it reacts only to ultraviolet rays, the color change will be different in the car where the window glass is UV-cut, when the hat or parasol is not exposed to ultraviolet rays, on a cloudy day or in the daytime when the amount of ultraviolet rays is small. Especially in the car, the color hardly changes.
1-2 Visible light dimming lens
Not only ultraviolet rays but also visible rays (light rays that can be seen by the eyes) react and the color of the lens changes.
Product names vary depending on the lens manufacturer and retailer.
Since the color changes with visible light, the color changes even in a car with UV protection. Even indoors, it has a very light color (visible light transmittance of about 90 to 80%).
1-3 Lens material and coating
Some are made by kneading a dimmer into the lens material, and some are made by applying a dimmer to the lens as a coating.
If it is made by kneading it into the lens material, there will be a difference in thickness within a single lens when the degree is increased, and "color unevenness" will appear during color development. On the other hand, the one made by coating the light control material does not have color unevenness caused by the difference in the thickness of the lens, and the color is evenly developed.
There are also disadvantages to the dimming function of the coating. If the coating is scratched or dented by hitting something, the dimming function of that part will deteriorate and color unevenness will occur. Even if scratches or dents are formed on the lens material that is kneaded into the lens material, the dimming function itself does not change.
2. Photochromic lens and UV protection
As explained in Vol.8 "Story of Lens Color" and Vol.9 "Story of Ultraviolet Rays", ultraviolet rays are invisible light, so even a dimming lens can cut UV rays firmly. It also prevents glare when it is developing color, so it is also effective as sunglasses.
According to the Japan Meteorological Agency, assuming that the amount of ultraviolet rays in fine weather is 100%, the amount is about 95% in sunny weather, about 80-90% in light cloudy weather, about 60% in cloudy weather, and about 30% in rainy weather. ..
Even on a cloudy day, the amount of ultraviolet rays is less than when it is fine, but the amount of reduction is smaller than when it is visible light, so you need to be careful about ultraviolet rays even on a cloudy day. Even when it is cloudy, if the sun is shining through the clouds, the amount of ultraviolet rays may be higher than when it is fine because the scattered light from the clouds is added.
Sunglasses that do not change color will be less active on cloudy days, but if you use a photochromic lens, the degree of color development will change depending on the amount of ultraviolet rays, so you can use dark sunglasses on sunny days and light sunglasses on cloudy days. Will be.
3. Prescription glasses with photochromic lenses
We accept prescription single focus lenses and bifocal lenses with a dimming function. Of course, you can create it without any degree.
You can use any frame you like, but please contact the store staff as there are differences in lens types and colors depending on the lens manufacturer.
4. Precautions for photochromic lens
So far, I have talked about photochromic lenses, but at the end, there are some points to note when actually using them.
◎ The density of the photochromic lens depends on the intensity and temperature of ultraviolet rays.
Color development is promoted when exposed to strong ultraviolet rays, but color development is suppressed when the temperature rises. Even if the ultraviolet rays are strong, the color tends to develop only slightly in summer when the temperature is high. To prevent glare in the summer, we recommend using sunglasses separately.
◎ It will take some time for the product to return to lighter from the darkened state.
It takes longer to fade in winter when the temperature is low and the color is dark. Motorcycles and cars are unsuitable for driving in dark places such as tunnels and indoor parking lots, and at dusk, and can be very dangerous in some cases.
◎ Be careful not to scratch the lens surface.
The photochromic lens gradually deteriorates over time due to the effects of ultraviolet rays, etc., causing a decrease in density and a change in color tone. The life of the dimming function is said to be 2 to 3 years. Please handle with care as scratches on the lens surface may accelerate deterioration.
◎ Storage in a glasses case
If the color is developed and stored in a place where light is blocked, such as a glasses case, the color may remain, but the dimming function is maintained. In that case, the color will disappear if you wait until the color fades naturally, such as by letting the color develop again and then returning it to the room.
[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%)