Do you know these sunglasses shopping knowledge?
How do you tell the anti-ultraviolet performance of the sunglasses?
QB2457-1999 and GB10810.3-2006 are now the unified standards for the production of sunglasses in China, which can ensure that at least 95% of UVA and at least 99% of UVB are blocked. If the sunglasses are sold in the country, the two standards will be shown on the certificate. The sunglasses that prevent ultraviolet rays have the following kind of identification commonly: "UV400": In other words, the average transmission ratio of ultraviolet light with the wavelength below 400nm through the lens is not more than 2."UV", and "anti-ultraviolet" means that the average transmission ratio of ultraviolet light below 380nm through the lens is not more than 2%. "100%UV absorption" means that the lens can almost 100% filter out all wavelength ranges of UV. The average transmission ratio is not more than 0.5%.
Are darker sunglasses easy to block UV rays?
It is not! The color of the lens only affects the amount of visible light received by the human eye, but ultraviolet light is invisible light, so there is no necessary connection with the amount of transmission. In other words, some transparent lenses, due to their material properties and special workmanship, can block UV rays, while some poor-quality sunglasses, which look very dark in color, may not block UV rays.
In modern China, "crystal eyeglasses" have been popular. This was because optical glass technology had not yet been mastered, and the only way to make lenses was to use natural materials. One part of the crystal lens is tawny. Wearing them can reduce a part of the visible light so that people have a "cool" feeling. In fact, crystals have a very high transmittance to UV rays and do not protect the eyes. This means that the color or shade of the lens has nothing to do with its ability to block UV rays. Not only that but wearing lenses that are too dark in the wrong setting can be dangerous.
Why will you feel giddy when wearing some sunglasses?
The common causes of dizziness are as follows:
Lenses Color: Wearing sunglasses with excessively dark lenses (low visible light transmission ratio) in daily environments (like indoors) for a long time can cause visual fatigue, which can lead to serious symptoms like dizziness and nausea.
Sunglasses frames: For example, the temples of the eyeglasses are too tight, which presses on the temple, leading to dizziness. Or it is caused by the discomfort of wearing the nose pad of the glasses.
Lenses processing problems: If the size of the lens is too large during processing, forced into the frame, the lens will be under such long-term distortion stress. The optical index of the lens will therefore exceed the standard. Wearing such lenses will cause dizziness or affect vision.
In addition to the above circumstances, it does not rule out that some people are not comfortable with the lenses of progressive dyed sunglasses.