8 common questions when choosing sunglasses
Last updated June 1, 2020
What are the meanings of the 1, 2, 3, and 4 on the sunglasses tag?
First, we need to understand the word: transmittance.
Transmittance, also known as the transmission coefficient, refers to the ratio of the luminous flux through the lens to the incident luminous flux. Directly speaking, it is the transmittance or transmittance of visible light.
For example, if a sunglasses lens has a transmittance of 40%, only 40% of visible light can pass through the glass into the eye.
According to the transmittance of visible light, the lens can be divided into 1-4 categories from shallow to deep:
The first type: light-coloured sunglasses; projection ratio 43%~80%
The lightest colour, shade and reduce the minimum luminous flux, generally used as a fashion accessory mirror
The second type: light shade mirror; transmittance 18%~43%
Lighter in colour, used on cloudy or cloudy days;
The third type: sun visor; transmittance 8% to 18%.
Most sunglasses belong to this level, suitable for outdoor activities such as seaside and mountain climbing;
The fourth type: special purpose sunglasses; transmittance 3%~8%
It is used in skiing, desert, electric welding and other environments.
According to the requirements, the driving mirror transmittance is more than 8%, so the fourth type of sunglasses cannot be driven by the car.
Some sunglasses can cause the wearer to fail to recognize the communication number or identify difficulties, resulting in a traffic accident because the transmittance of these sunglasses is not acceptable.
How do you know the UV protection performance of sunglasses?
QB2457-1999 and GB10810.3-2006 are the unified standards for domestic sunglasses production, which can ensure that at least 95% of UVA and at least 99% of UVB are blocked. As long as it is a sunglasses sold in China, these two standards will appear on the certificate.
UV-resistant sunglasses generally have the following logos:
“UV400”: the average transmittance of ultraviolet light having a wavelength below 400 nm through the lens is not more than 2%
“UV”, “UV protection”: indicates that the average transmittance of ultraviolet light having a wavelength below 380 nm is not more than 2%.
“100% UV absorption”: It means that the lens can almost 100% filter out the ultraviolet rays in all wavelength ranges, and the average transmittance is not more than 0.5%.
Is the darker the colour of sunglasses can block more UV rays?
Not! The colour of the lens will only affect the visible light received by the human eye (compared to the 1-4 categories mentioned above), but the ultraviolet lightis invisible, so there is no necessary connection with the amount of transmission.
In other words, some transparent lenses can block UV rays because of material properties and special processes, while some inferior sunglasses look dark in colour but may not block UV rays.
In modern China, “crystal glasses” (also known as stone mirrors) have been fashionable. Because people have not mastered the optical glass technology at that time and can only use natural materials to polish them into lenses. Some of the crystal lenses are brown, which can reduce some of the visible light after wearing so that people have a “cool” feeling; thus, there is misinformation of “crystal care”.
The crystal has high transmittance to ultraviolet light and does not protect the eyes; this also means that the “lens” has no colour or colour, regardless of the ability to block ultraviolet rays.
Not only that but wearing too dark lenses in unsuitable scenes can be dangerous.
For example, when driving in summer, the sun is powerful, and many owners choose dark sunglasses to block the sun. However, wearing dark sunglasses is easy to filter out bright objects, and the size of the front body is not accurate, which affects the judgment of the distance. In an emergency, dark sunglasses will delay the imaging of the optic nerve, resulting in slow response and significantly reducing the driver. Sensitivity to the surrounding conditions allows the driver to make a wrong judgment, resulting in a dangerous situation.
How to choose colourful sunglasses?
Many consumers mistakenly believe that the colour of the lens is like the colour of the clothes, but the aesthetics are different, but the practicality is neglected; in fact, the different lens colours have different effects on the human eye’s vision.
Here, let’s first understand why there is colour.
As we all know, white light is composed of seven colours of “red-orange, yellow, green, blue, and purple,” each with a different wavelength.
When a lens absorbs light of other wavelengths and only transmits light of a particular wavelength, a specific colour appears. And when we look at the world through the lenses of this colour, it is like adding a filter when taking pictures.
Therefore, lenses of different colours have different meanings for the user.
From a professional perspective, brown and grey lenses are first choice. These two colours have good filterability and colour perception, and can better distinguish various colours.The brown colour of the lenses is soft so that the eyes are not easy to fatigue; in the case of air pollution and fog, it can increase the contrast between light and dark, and the wearing effect is good.The gray lens is gentle and natural because it can absorb evenly on any chromatogram. It will only darken when viewing the scene, there will be no noticeable colour difference, and it can show a more natural feeling, suitable for most people.
Second, dark green, it can increase the green light reaching the eyes, so that the wearer has a relaxed and comfortable feeling, suitable for people who are prone to eye fatigue. But sometimes the colour of the scene will change after passing the green lens.
The choice of yellow, red, pink, light blue, etc. should be cautious, because they are more decorative than practical, and to some extent affect the ability of the human eye to distinguish the surrounding colours.
But now many fashion youths will choose the favourite “jelly colour” lenses to “concave shape.” Of course, it is no problem for purely decorative use; if you want a pair of sunglasses that are comfortable to wear and more practical, we do not recommend this type.
Is polarized sunglasses better than ordinary sunglasses?
The polarizer is only one type of sunglasses. The polarizer can reduce the reflection; it can be worn when driving, fishing, skiing, water skiing or cycling, which can improve the clarity of the field of view. For patients after cataract surgery and for those who are sensitive to light, choosing polarized sunglasses can also enhance visual comfort.
However, polarizers also have limitations: for example, wearing polarized glasses may not be able to see the LED display, GPS and mobile phone screens.Polarized sunglasses cannot be used for pilots, crew, etc.
Therefore, each type of sunglasses is only applicable in different fields. You should choose according to your actual needs, and you can’t merely distinguish between “good and bad.”
Sunglasses is without a degree, why do some sunglasses wear dizziness?
Common reasons for wearing dizziness in sunglasses are as follows:
Lens colour: In the daily environment (such as indoor), the lens is too dark (the visible light transmittance is too low) for a long time, which causes visual fatigue, and severe symptoms such as dizziness and nausea may occur.
Frames of sunglasses: for example, the temples are worn too tightly, pressing the temples, causing dizziness, or the wearing of the stilettos of the glasses is caused by discomfort.
Lens processing problem: sunglasses lens is not luminosity (except for myopia sunglasses), but if the size of the film during processing is too large, forcibly squeeze into the frame, the lens is under the stress of long-term distortion, the optics of the lens The indicator will exceed the standard. Wearing such a lens can be dizzy and affect vision.
In addition to the above, it is not excluded that some people feel uncomfortable with progressively dyed sunglasses lenses.
Is the lens of the sunglasses excellent or bad?
Each type of lens material has its own merits and cannot be easily distinguished by “good or bad.”
For example, although the glass lens is wear-resistant and has excellent optical properties, the use of the lens is gradually reduced because of the heavy weight of the lens.
Resin lenses (such as CR39 material) are easy to colour, light and impact resistant, and become one of the mainstream materials for fashion sunglasses; however,
resin lenses are prone to chipping during the edge cutting process, and they will still break when they encounter significant impact.
In this regard, the PC lens is superior to the resin lens, and its characteristics are lightness, excellent colouring performance, stronger impact resistance, and the disadvantage is low abrasion resistance.
TAC sunglasses lenses are generally used in China. TAC (Triacetyl Cellulose) is one of the better light-transmitting polymer materials. TAC as a sunglass lens has the characteristics of acid and alkali resistance, lightweight and high-cost performance, but its weak wear resistance has become a weakness of TAC lenses.
Nylon sunglasses are used in the production of sports sunglasses. They have high elasticity and excellent optical quality. They are incredibly resistant to impact and have professional protective purposes; however, they have high production costs.
Is there any taboo with sunglasses?
Particular attention should be paid to the following people when using sunglasses:
Glaucoma patients: When wearing sunglasses, the visible light entering the eye is reduced, and the pupil is naturally enlarged. This change of pupil does not affect healthy people, but for glaucoma patients, it increases the obstacles of aqueous humour in the eye, which can quickly induce acute episodes of glaucoma, redness,eye pain, headache, nausea, vomiting, sharp decline in vision, etc. symptom.
Therefore, glaucoma patients or suspected glaucoma are not recommended to wear sunglasses.
Colour blind patients: full-colour blind wear sunglasses do not have much impact. However, some patients with colour blindness cannot distinguish between several colours. When wearing sunglasses, they are even more incapable of distinguishing colours.
There are also night blindness, optic nerve retinitis and other people are not suitable for wearing sunglasses.
Also, do not wear sunglasses indoors.
Because the sunglasses will make the eyes of the people in relatively dark light, then the pupil will subconsciously dilute, and the vision will be affected. It is natural to watch the object. For a long time, the eyes are over-adjusted, and it is easy to cause symptoms such as visual fatigue and photophobia.
Director Wang Jiawei is a typical example. He said: “Sunglasses can be said to be a price for filming for so many years. I usually write scripts during the day,filming at night, eyes are used to the darkness; if you take off the sunglasses, you will not see me. The eyes — will see tears because my eyes are too sensitive to the light.” So he can only show people with sunglasses.
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