Ozone - Sun - Eyes (3)

Solar Protection

 

 

The lenses made with glass have solid tint in it to absorb the radiation, usually they absorb the ultraviolet light under 350 nm. The colors are usually green, brown, grey. The color has nothing to do with the absorption, but rather with the individual liking, and with the optical deficiency. The  hypermetropic should have green tint, the myopic should have a brown color, the grey color, is the tint that absorb evenly the visible spectra, which means that the colors are not as much modified as with the other tints. The lens can have a surface coating with anti-reflection layer, which diminishes the reflection on the lenses ( mirror effect ). Lenses can be mirrored, to reflect the radiation on top of the absorption. Optically speaking you have two kinds of lenses, one is optically polish without any optical defects, or they can be none optical. The lenses polished optically are the best because they do not have little optical defects who can produce headache, eye strain etc.. Some people can simply not wear the none optical lenses.

The plastic lenses are colored by dyes. They scratch easily, but they are light weight, especially with the big frame, otherwise the all frame would be too heavy.The absorption is usually less under 400 nm, and is no good for the I.R. The plastic lenses can be, made with any colors you may think of, even two or three colors in the same lens, and this with different shades. The plastic lenses can be mirrored for the purpose of reflecting the radiation.

Recently you can find contact lenses with tint for the sun, they are made with a special dye, to absorb the radiation. These only protect the cornea but not the conjunctiva. They are not recommended for the high altitude etc... .

 

POLARIZING LENSES :

The polarization effect is the fact that the rays are oriented in the plan right angle of their direction by the reflection on any transparent surface like the water. (The vibrations are in one axis, in one direction only at right angle of the line of sight.) We can polarize the light also through certain crystals , and if we put these crystals at right angle of the polarization from the transparent surface, we can almost cut completely the reflection from this surface. This effect is quite striking in water , where the fisherman can see the trout without any reflection. Otherwise the Polaroid lenses work just like ordinary lens with the same absorption of the sun rays, they can be made in plastic or organic lenses or like laminated lenses where you have a plastic sheet between two layers of glass. With the reflection on transparent surface the polarization takes place only on certain angle depending of the refraction index of the material this surface is made, the 'BREWSTER ANGLE' , ~ 53 deg. for the water .

Polarization effect by reflection on water.

 

 

 

 

 

MELANIN LENSES :

The melanin lenses have active pigment called melanin which are the pigment of the body to protect from near visible rays of the sun. The melanin lenses are polarized lens or not polarized . They are made of organic material (plastics) lenses and are of green colors and not to dark in colors but cut off the glare form the reflections for the polarized lens, for the non polarized lens they works just like ordinary sun lenses with a special additive to cut the U.V. that is the artificial melanin. Just in the same way the body would protect himself from the sun rays. They protect well for the U.V. under 400 nm.

 

PHOTOCHROMIC LENSES :

The photochromic lenses, are the lenses which get dark in the sun and clear up indoors. There are a lot of different brands who are more and less quick to change colors, they may change color in grey bluish tint or brown tint. Sun lenses are usually made of glass and have a basis tint in it, the optical lens are clear and have quick change of tints and big or medium range between clear and dark. We just have the brand new photoslim lens that is 30% thinner and very quick to darken, and work behind the windscreens of cars. The glass lenses have a good absorption in the U.V. but no good in the I.R. The photochromic s organic lenses, work quite well but they are used as ophthalmic optical lens because of there price. They are more sensitive to change in the environment like temperature and the amount of U.V. They are also not so stable time wise, after 2 to 4 years they lost 25% of their effect . They also do not absorb the U.V. as well as the glass lens.

 

As a conclusion, less pigmentation you have, younger you are, darker should your sun lenses be, they should absorb all the U.V. under 400 nm. and have no optical defects to disturb the quality of your vision. You may have special lenses to have a better contrast and special tint for different purpose like driving, you may appreciate also the anti-reflection coating, which stops the mirror effect on your lenses, to make them more transparent. .

Emission Dolce Vita tsr 04/02/2008