In the summer, I have arrived in the season with sunglasses. Many female friends will buy a variety of sunglasses. So, do you really understand the little knowledge of sunglasses?
Many people know that ultraviolet rays can sunburn the skin, but they don't know that their eyes will be "sunburned." The eye is the most delicate part of the human body. It is easily sunburned by ultraviolet rays. The sun has a cumulative effect. Over time, it will be harmful to the eyes. It is called "chronic light damage" in medicine.
The main function of sunglasses is to block the damage of ultraviolet rays to the eyes, not just to improve the visual effect. This requires that the transmittance of sunglasses to ultraviolet light in the sun is as low as possible, that is, the higher the reflectance and absorption rate, the better.
Light in the solar spectrum with wavelengths from 380 nm to 780 nm is called visible light, including red-orange, yellow, green, blue, and purple. The wavelength greater than 780 nm is invisible to the human eye and is called infrared; the wavelength is less than 380 nm. Some human eyes can't see it anymore. It is called ultraviolet (UV). According to different wavelengths, ultraviolet light can be divided into UVA, UVB, UVC and vacuum ultraviolet. Sun damage to skin and eyes is mainly caused by UVA. UVB and UVC caused by ultraviolet rays.
UV protection is an essential function of sunglasses. It has nothing to do with the color and transparency of the lens. It is usually achieved by coating. It is usually in the following three ways.
- Mark "UV400": It means that the lens can block ultraviolet rays and visible light with a wavelength of 400 nm or less; as long as the ultraviolet light transmitted through the lens is less than 2%, it is qualified.
- marked "UV", "anti-UV": means that the lens can block ultraviolet light below 380nm; as long as the ultraviolet light through the lens is less than 2%, it is qualified.
- marked "100% UV absorption": indicates that the lens has a 100% absorption of UV light; but in fact, the UV light through the lens is less than 0.5%, even qualified.
Buy sunglasses must not only be cheap and style, but you must also choose carefully!
Choose sunglasses notes
- Wear sunglasses not only to play cool but more importantly to protect the skin around the eyes and eyes from the sun's UV rays. The effects of ultraviolet light on the eye include cataracts, pterygium (a white neoplasm on the cornea), and inflammation of the eye (such as photokeratitis and photoconjunctivitis).
- Sunglasses that provide 99% to 100% protection for UVA and UVB will greatly reduce eye damage caused by exposure to the sun.
- Sunglasses that provide 99% to 100% protection for UVA and UVB must be selected. Sunglasses labeled "UV 400" or "100% UV absorption" on the label indicate that the lens blocks all UV light (including UVA and UVB).
- The color of the lens has nothing to do with the ability to filter ultraviolet rays. Wearing dark glasses without UV protection will enlarge the pupils of the eyes and increase the risk of UV damage to the eyes, so don't think that you can choose glasses with dark lenses.
- The transparency of the lens with low color is low. When the sun is violent or worn for a long time, choose sunglasses with low transparency. Choose from grey, Brown or Greenish-grey lenses when driving in the sun or during the day; yellow lenses are available for driving on cloudy and dusk; and brown lenses for golf.
- It is not recommended to choose brightly colored lenses such as orange or pink, because the image will be color cast (that is, the visually visible color is different from the actual color).
- Polarized lenses selectively filter UV light reflected from snow, water and beach surfaces for skiing and water activities.
- Baby can also wear sunglasses, and there is no age limit for wearing sunglasses.