The categories of sun lenses

The category of the lens depends on a value called Visible Light Transmission (VLT) or Tv (transmittance value). This is a measure of how much light the lens lets your eyes pass through and is expressed as a percentage.


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The category of the lens depends on a value called Visible Light Transmission (VLT) or Tv (transmittance value). This is a measure of how much light the lens lets your eyes pass through and is expressed as a percentage.
Consequently, a VLT value of 1% indicates very dark lenses, while a VLT of 100% means that all the light is passing and in this case it is a transparent lens.
Sunglasses must comply with specific characteristics and all sun lenses must carry category information on the label.
The categories are divided into:
CATEGORY 0; 80-100% TV - Transparent / clear - Absorption 0-20%
Usage: very limited reduction of solar glare. For fashion, indoor use or evening hours.
CATEGORY 1; 43-80% TV - Clear / semi-clear - Absorption 20-57%
Usage: limited protection against solar glare. For use on cloudy days.
CATEGORY 2; 18-43% TV - Dark - Absorption 57-82%
Usage: good protection against sun glare, average sun exposure.
CATEGORY 3; 8-18% VT - Very Dark - Absorption 82-92%
Usage: high sun protection, strong brightness.
CATEGORY 4; 3-8% TV - Very dark / opaque - Absorption 92-97%
Use: very high protection against extreme sunlight, for example at sea, on snowfields, in the high mountains or in the desert.
Suns lenses are often equipped with anti-UV filters that guarantee protection against UV rays up to 400 nanometers. Very often the UV protection is given by the base material of the lens, so the lens is already basic with UV protection beyond the coloring.
It should be known, in fact, that the screen against ultraviolet is not given by the color, but by the filtering power of the sunglasses, indicated precisely by the category.
Furthermore the coloring of the lens helps to increase the protective factor of the glasses as, by reflecting part of the light radiation, it reduces the amount of harmful rays that reach the eye.
In general, it can be said that the protection increases the darker the lens is. It is therefore 





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