The most important function of sunglasses is to protect people’s eyes. Thus, we need to choose the appropriate transmissivity and UV protection function.
Sunglasses can be divided into Category 0, 1, 2, 3 and 4 according to different lens transmittance.
According to the standard, the sunglass transmittance is divided into 5 grades. The higher the grade, the higher the light barrier.
For example, if the sunglass transmittance is 40%. That is, only 40% of the visible light can pass through the lens and enter the human eye.
So according to the transmittance of visible light. Lenses can be divided into the following 5 categories from shallow to deep:
Cat.0: Transmittance 80%~100%
Fashion lens or light sun protection, indoors, cloudy or at dusk.
Cat.1: Transmittance 43%~80%
Suitable for low-intensity sunlight and cloudy weather. It is rich in color, suitable for use with all kinds of clothing, and has a strong decorative role.
Cat.2: Transmittance 18%~43%
Light color, suitable for moderate sunlight, overcast or cloudy days. The most common category of general-purpose sunglasses.
Cat.3: Transmittance 8%~18%.
For strong sunlight, seaside, mountains, summer outdoor activities. Such as driving and fishing.
Cat.4: Transmittance 3%~8%
The lens has the deepest color. It is only suitable for extremely strong light, such as alpine skiing, glaciers, deserts and other special environments
Besides, when driving, the sunglass transmittance should be greater than 8%. Thus, the Cat.4 sunglasses cannot be worn by the driver.
Also, sunglasses with UV protection function generally have the following marks:
UV400: UV with wavelength below 400nm, the average transmittance through the lens is not more than 2%
UV380: UV with wavelength below 380nm, the average transmittance through the lens is not more than 2%
Nearly 100% UV absorption: It means that the lens can almost 100% filter out ultraviolet rays in all wavelength ranges. The average transmittance shall not be greater than 0.5%.
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