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In the heat of summer, watermelon, sunblock, sunglasses — these are the labels. Buy a watermelon every two days and a sunscreen every year. How often do you change your sunglasses? The frequency of changing sunglasses depends on whether there is a new style that suits you better.
Sunglasses also have a shelf life
Sunglasses are safe to wear for two years, the Daily Mail reported, citing researchers. Sun exposure varies across the globe, with the highest uv levels in tropical countries and regions, which are high even in winter, meaning the glasses’ uv protection degrades faster there. In addition, people in the southern hemisphere change their shades more often than people in the northern hemisphere. Not only does prolonged sun exposure affect sunglasses’ ability to protect against UV rays, the lenses are also more likely to crack, the researchers said.
So experts recommend changing your sunglasses every two years.
Weaker reflections indicate aging
There are two types of sunglasses. One is made of colored glass such as yellow and blue, which absorbs energy and refracts light. The other is a coating on the lens surface, which reflects uv light. The shelf life of sunglasses refers to the latter category of sunglasses. On the market, more than 80 percent of glasses are coated.
In general, this coating is combined with glass by physical vapor deposition. The coating is generally made of gold, silver, copper and other metal materials, and the metal materials will undergo oxidation, which will lead to their poor uv protection.
However, different brands of glasses, the production method is not the same, the high price of glasses, will be coated with several layers of coating film, or alloy material coating film, stability will be better, not easy to oxidation. Just take your glasses and look at the reflection. The newly bought glasses look like a mirror. If the reflection gets weaker, the coating has been oxidized or even fallen off. In the industry, it is generally believed that glasses will age to different degrees in normal use due to sun exposure, lens wear and so on. Therefore, if glasses wear seriously, they should be replaced in time to avoid the impact on vision
Sunglasses’ extended service hurts eyes
What’s the harm if you wear “overage service” sunglasses for too long?
In the worst case, it’s actually uv rays coming in and affecting the eyes.
According to an article published by the World Health Organization (WHO) in The journal Ultraviolet Radiation and Human Health, 5 percent of the 18 million people worldwide who go blind each year due to cataracts are caused by ultraviolet radiation. Ultraviolet light can also cause other serious eye diseases-keratitis, retinal damage, cataracts, macular degeneration, snow blindness, and so on.
Fortunately, most people don’t wear sunglasses for very long, even when the coating is peeling off. However the sunglasses outside shelf life, also easily let a person produce the condition such as eye fatigue, eye is dry, eye acerbity, still may bring about myopia aggravation.