What is the transmittance of lenses

Don't know you ever notice when buying sunglasses packing, usually write the transmittance above, a total of 1, 2, 3, 4, these, what this parameter represents the mean? 6201/13 brown ray-ban RB4242 unisex eyeglass frame transmission than transmittance is also called transmission coefficient, the luminous flux through the material or medium or auxiliary flux to the incident flux. The transmittance of a material depends on the direction of the incident light, the molecular structure of the materials and the thickness of the material and other factors. Specific classification according to the degree of lens of pervious to light transmittance, is divided into four categories, can be called 'transmittance classification'. 1, 43% ~ 80%. 2, 18% ~ 43%. 3, 8% ~ 18%. 4, 3% ~ 8%. As requested, driving goggles transmittance is greater than 8%, so the class 4 sunglasses can't drive. For uv protection, the former three kinds of uva allowed by 5%, the fourth class uva allowed through 0. 5%. Uvb rays are allowed by 1%. And a classification, could be called 'sunglasses' category, special sunglasses, classification based on light transmittance is also, but the three categories. 1, light color sunglasses, pervious to light more than 40%. 2, sun glasses, pervious to light 8% ~ 40%. 3, special-purpose sunglasses ( Skiing, mountain climbing, beach, etc. ) , 3% ~ 8%. With light color sunglasses and a sunshade lens, have traffic lights to identify demand, three color shall be higher than 8%. Ray-ban sunglasses RB8056 men 175/6 q hawksbill knowledge development: what is the uv protection of polarized sunglasses ultraviolet prevention function of polarized sunglasses, the express way generally have the following: a) Labeled 'UV400' : this means that polarized sunglasses lenses for uv cutoff wavelength of 400 nm, namely the wavelength ( λ) Under 400 nm maximum of the spectral transmittance of tau Max ( λ) No more than 2%; b) Labeled 'UV', 'anti ultraviolet' : this says polarized lenses for UV cutoff wavelength of 380 nm, namely the wavelength ( λ) Under 380 nm maximum of the spectral transmittance of tau Max ( λ) No more than 2%; c) Labeled '100% UV absorption' : this says the polarized sunglasses lenses is 100% for UV absorption function, namely in the UV range of average transmission ratio is not greater than zero. 5%. To achieve the above requirements of polarized sunglasses, is in the true sense polarized sunglasses for uv protection function.
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