In the hot summer, watermelon, sunscreen, sunglasses, all the standard.
Two days to buy a watermelon, sunscreen in a year, a: how long does it take your sunglasses in a pair?
We change the frequency of the sunglasses, new depends on ever more suitable for you to.
Recommended reading: open the right way: a film, that is cool sunglasses!
Sunglasses also has expiration but do you know?
Sunglasses also has 'expiration date', if it work to her not only not protection, it will cause harm to the eyes.
Exposure can affect the sunglasses uv protection ability of the university of Sao Paulo, Brazil, the researchers in Europe, Australia, New Zealand and South America to do simulation experiment, the sunglasses under the sun simulator, 30 cm distance markers, 'sun' 50 hours continuously, look at the lens degradation degree of uv protection ability.
The daily mail quoted researchers reported, sunglasses to wear or security for two years.
Sunshine is different in different areas of the world, tropical countries and the area of the highest uv, even in the winter is also high, means that the sunglasses uv protection function degradation is faster in these places.
In addition, some residents in southern hemisphere sunglasses frequently than people in the northern hemisphere.
Researchers also said that sun long time not only affect the sunglasses uv protection ability, lenses were also more likely to rupture.
Researchers at the university of Sao Paulo, Brazil, advice, need to change a pair of sunglasses every two years.
Reflective explain the study on aging become weak?
Sunglasses has two kinds, one kind is the lens made of yellow and blue colored glass, energy absorbed by the body, the refraction of light;
Another kind is adding coating on the surface of the lens, the coating reflect ultraviolet light.
Dark glasses after the shelf life of refers to the kind of sunglasses.
On the market, more than eighty percent of the sunglasses are coating.
In general, this layer of coating using physical vapor deposition method is combined with glass.
Coating is generally made of gold, silver, copper and other metal materials, and metal oxidation happens, this will lead to weaken their uv protection.
But different brands of sunglasses, producing method is different also, price of sunglasses, will be coated layers of coating, or coating of the alloy materials, stability will be better, not prone to oxidation.
As long as take sunglasses glance look at the situation, new sunglasses as it like a mirror, if reflective case has weakened, explain coating has been oxidized even fall off.
Zhejiang province bureau of quality and technical supervision issued on April 20, 2012 on sunglasses in the evaluation of zhejiang province product quality supervision and inspection rules clearly listed the light transmittance, the average transmittance, color limit, traffic signal transmission than the four transmission characteristics for mandatory inspection items.
The transmission characteristics are related to coating, but the evaluation rules did not indicate the specific inspection standard.
No mention in the national standard shelf life.
In the industry generally believe that glasses because the sun, in the normal use of lens wear, etc. , using time more than 1 year lenses have different degrees of aging, so if worn glasses should change in time, avoid to affect vision.
Sunglasses overterm service eye injury if worn for a long time served 'overage' sunglasses will what harm is there?
In the worst case, in fact, the ultraviolet ray march into the affect to the eyes.
The world health organization (who) published the ultraviolet radiation to human health, the article points out that the 18 million people worldwide each year because of cataract blindness, 5% were caused by ultraviolet radiation.
Ultraviolet ray also can cause other serious diseases -
Keratitis, retinal damage, cataracts and macular degeneration, snow blindness, etc.
Fortunately, most people wearing sunglasses will not be too long, even coating have fall off, also not long face to face with ultraviolet light.
Shelf life outside of the sunglasses, however, also easy to produce visual fatigue, dry eyes, dry eyes, such as conditions, can also lead to myopia aggravating.