Sunglasses: protection against UV rays

Sunglasses are one of the main fashion accessories to characterize your "look", but too often their function of protecting the eyes from ultraviolet (UV) rays is underestimated.

In fact, it should not be forgotten that sunlight contains radiation which, in the long run, can damage the retina and cause even serious damage such as cataracts or inflammation of the cornea.

For this reason, when purchasing a new pair of sunglasses, in addition to the aesthetic aspects linked to personal taste, it is a good idea to check that the level of protection of the lenses is adequate to guarantee the well-being of our eyes.

What are UV rays

Ultraviolet (UV) radiation is a component of sunlight characterized by very short wavelengths, between 100 and 400 nanometers (nm), and is usually divided into three main categories: UVA (315-400 nm) UVB (280 -315 nm) UVC (100-280 nm)

UVA rays represent approximately 95% of the ultraviolet radiation that reaches our eyes and can cause damage to the retina, cornea and, of course, the skin. UVB rays are less present but even more insidious because their effects are generally deeper and longer lasting. Finally, UVC rays would be the most dangerous for damaging human eyes and skin, but fortunately they are blocked by the ozone layer of our atmosphere, so they do not require specific protection (except in particular cases; for example to protect themselves from light emitted by an electric soldering iron).

Which lenses protect against UV rays

There are various levels of protection against ultraviolet radiation, but it is essential to point out that counterfeit glasses or those without CE certification are most likely equipped with lenses without any level of solar filter and can therefore be very dangerous for the wearer.

The original glasses with CE certification , in addition to other quality requirements, guarantee adequate protection up to 380 nm, therefore including the UVA and UVB range.

Attention: to be authentic, the CE marking must be engraved indelibly and legibly on the surface of the glasses; if it is applied only via adhesive, and is therefore removable, it is certainly a fake.

To make the presence of the anti-ultraviolet filter more explicit, the lenses can bear the indication " UV400 " (to mean that they block UV radiation up to 400 nm) or alternatively " 100% UV protection "; the two definitions are equivalent.

Lens classification and UV protection

Sunglass lenses are divided into 5 categories based on their ability to reduce the brightness reaching the eyes. Therefore, moving from the lightest to the darkest lenses, we find:

• Category 0: 80-100% of light passing through the lenses
• Category 1: 43-79% of light passing through the lenses
• Category 2: 18-42% of light passing through the lenses
• Category 3: 8-17% of light passing through the lenses
• Category 4: 3-7% of light passing through the lenses

In this case, the parameter taken into consideration for the classification is the entire light spectrum and therefore it is important to underline that there is no direct relationship with the degree of protection against UV .

It is therefore essential to understand that it is not at all a given that darker lenses offer greater protection . Indeed, wearing dark lenses without UV protection causes the pupils to dilate, exposing the inside of the eye and the retina to more harmful radiation. At least, if we don't wear sunglasses, the pupil narrows and allows fewer harmful rays to enter.

Usually lenses with UV400 protection belong to Category 3 (or 4), allowing optimal protection even against visible light in very sunny contexts. But, as mentioned, UV400 protection can also be found on lighter lenses.

UV protection is typically present inside the lens or applied on its external surface: for example some materials such as polycarbonate already contain a filter inside them which ensures 100% protection from UV rays, while for other materials such as plastic CR39 it is normally necessary to add a filter coating on the surface.

Do polarized lenses protect against UV rays?

The two types of protection should not be confused. Polarized lenses are made to avoid glare from light reflecting off flat surfaces such as snow, water, sand or asphalt. The anomalous and annoying reflection that is generated is filtered by the lens, improving the visibility and quality of the colors perceived in this type of situation.

The two protections are therefore not equivalent, but can be complementary to obtain greater visual comfort.

Conclusions

Ultimately, when choosing sunglasses it is essential not to neglect an essential element such as protecting your eyesight .

Even if apparently pleasant, counterfeit glasses or glasses of dubious origin or quality, can in the long run cause serious damage to the eyes, in particular due to the effect of ultraviolet radiation.

The color of the lens or its degree of darkness does not necessarily correspond to an effective filter against UVA and UVB, so it is best to pay attention to the manufacturer's specifications, so that an aesthetic choice is also healthy.