The cat­e­gories of sun lens­es

When we talk about cat­e­gories of sun lens­es, we re­fer to the per­cent­age % of light that reach­es the eye when it pass­es through a lens.

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