Transmittance, also known as transmission coefficient, refers to the ratio of the luminous flux through the lens to the incident luminous flux. Simply speaking, it is the transmittance or transmittance of visible light.
For example, if a sunglasses lens has a transmittance of 40%, that is, only 40% of visible light can pass through the lens into the eye.
According to the transmittance of visible light, the lens can be divided into 1-4 categories from shallow to deep:
The first type: light-colored sunglasses; transmittance ratio 43%~80%
The lightest color, shade and reduce the minimum luminous flux, generally used as a fashion accessory mirror
The second category: light sun visor; transmittance 18% ~ 43%
Lighter in color, used on cloudy or cloudy days;
The third categories: sunshade; transmittance 8% to 18%.
Most sunglasses belong to this level, suitable for outdoor activities such as seaside and mountain climbing;
The fourth categories: special purpose sunglasses; transmittance 3%~8%
It is used more in skiing, desert, electric welding and other environments.
According to the requirements, the driving mirror transmittance is more than 8%, so the fourth type of sunglasses can not be driven by the car.
Some sunglasses can cause the wearer to fail to recognize the communication number or identify difficulties, resulting in a traffic accident because the transmittance of these sunglasses is not acceptable.