Anyone who spends a lot of time outdoors for her work, leisure and sports, must protect his eyes against the glare and especially against Ray ultra-violet (UV), light blue and infrared (IR)

Glasses of very good quality and are sufficiently large an absolute requirement, simple dark tinted lenses offer no protection against UV radiation, on the contrary, they may not represent a risk factor.

Sun protection is becoming increasingly important

The protection of the ozone layer is decreasing, but also leisure and sports activities are more frequent in outdoor sun protection make it more useful. In addition to the skin, these are the eyes that react to radiation outside the visible light, especially in the field of ultra-violet (UV). Because the eye is not only exposed to direct radiation, but also rays reflected from snow surfaces or bodies of water, the eye is even more exposed.

The dark lenses do not protect

The man against the light since the dawn of time, then, for protective masks, and later by dark glasses. We now know that the dark glasses without UV protection will not protect the contrary, they add to the damage: the pupils widen because of the darkening and more dangerous rays entering the eye.

Solar radiation in the atmosphere

Solar radiation - that is, according to the quantum theory of elementary particles without mass (light quanta, photons) - is the provider of the most important energy in the earth. The visible part of radiation - from 380 to 780 nanometers (1 nm = 1 billionth of a meter = 0000'0001 mm) wavelength - is perceived by man from purple to red, depending on the length of wave. The waves below 380 nm are part of the ultra-violet radiation (UVR). Above 760 nm starts the infra-red radiation (IR).

The short-wave radiation UV (200-380 nm) has the power to form pigment in the skin and trigger chemical reactions. IR radiation of long wavelength (780 to 10,000 nm) falls in the area of creating heat rays.

While visible light and IR rays come onto the land almost without hindrance, this is not the same with much of the UV rays, which are absorbed for the most part by the ozone layer of the atmosphere. The decline of this layer filter must increasingly be offset by protective measures. Too much UV radiation can lead to skin cancer, eye irritation and according to the latest scientific discoveries to cataracts.

In stark sun, accompanied by a glare Therefore, it is easily sunglasses. UV protection is also needed by day "white". 50% of UV rays still reach us through a large cloud.

The division of radiation that concerns us is:

infra-red

U.V. A 315 nm - 400 nm

U.V. B 280 nm - 315 nm

U.V. C 100 nm - 280 nm

  1. VISIBLE 400 nm - 780 nm

I.R. 780 nm - 1 mm

As you can see, the UV rays are divided into three parts:

U.V. A 315 nm - 400 nm

UV-A are responsible for tanning without burning the skin. They create a fluorescence of the lens (lens of the eye) and reduce contrasts.

U.V. B 280 nm - 315 nm

UV-B establish vitamin D and are responsible for sunburn, conjunctivitis and keratitis. 

U.V. C 100 nm - 280 nm

UV-C are responsible for sunburn, conjunctivitis and keratitis (snow ophthalmia or coup d'arc). They also have an effect on the retina. They are very dangerous for the holders of contact lenses, and can cause skin cancer. It should be noted that there is sometimes confusion: UVC are confused with UVA

Blue light "dangerous"

Wavelengths of 380 -500 nm. are perceived as blue. Some experts advocate the view that blue light immediately after UV radiation in the spectrum could be dangerous for the human eye. The scientific evidence is still lacking, and the legislation specifically mentions that even in extreme conditions (high mountain) should not count on a safe. The standard of "UV-400" was still required from the manufacturers of sunglasses. European legislation requires that this statement could only be relevant if the glass did not move into this area more than 0.5% of the radiation.

In contrast UV invisible, light blue (visible) can be filtered by optical means. The reduction of blue light depends on the color of glass. The orange-brown glass best meets that condition.

A too high absorption of blue light causes a distorted perception of color. Less known than the UV, it is not blocked by the natural filters of the eye, and a source of early aging of the retina.

Protection against infra-red radiation

When a person looks or repeatedly for a long time the sun without adequate protection for the eyes, photochemical damage to the retina may be accompanied by thermal injury (radiation in the visible high-level and near infrared causing warming that can literally burn exposed tissues). Burns or photo coagulation destroy the cones and rods, creating a small blind area. The danger for the view is important because the retinal injuries occur without the sensation of pain (there are no pain receptors in the retina) and visual effects occur several hours after the damage is done.

In principle, there should be a danger to the eye, because the IR are not detected by the eye, so the ward is not closed to protect the retina of strong IR sources.

More fashion or protection?

Sunglasses do not only their work, they are indeed also fashion accessories appreciated. The range of models is all the greater.

Are not only important effect of the UV absorption and an appropriate color, but also the size of glasses. Sunglasses with small round glasses can be stylish, but they do not fulfil their protective function imperfectly, radiation side, and especially since the top may reach the eye. Are the perfect glasses eyebrows to rise and go sideways at least to the edge of the face. Glasses to provide lateral protection perfect protection against the rays. They are a perfect protection against UV rays, skiers are exposed not only to direct radiation on the snow, but also ray side. One disadvantage of these protections side is the restriction of the visual field side, which may represent a security risk if we ski on a busy track. For the skier from hiking, walking on a glacier or the mountaineer, this problem is of less importance. What is important to the use of glasses side shields that close almost completely the space between the face and glasses, is the effect of filtering IR rays. IR radiation can lead to an accumulation of heat behind the glass.