How to choose sunglasses

03/06/2020

Many think that the color of the lenses in sunglasses is something uniquely aesthetic, but nothing is further from reality. The color of the glass we choose will cause the absorption of a part of the spectrum of visible light to vary and therefore the perception of the landscape tone. Therefore, each of the different colors will be better adapted to a certain type of activity. These are the parameters that must be taken into account to choose our sunglasses.

1. The color of the glass

Leaving personal preferences aside, the glass filter has some characteristics that make it recommended for certain environments:

• Gray: respects natural colors, making it a good option for driving.
• Green: does not distort colors too much and does little to interfere with clarity of vision, making it suitable for water sports.
• Brown: filters the blue color and increases the contrast. That is why it is useful in sea and mountain areas with very clear days, as well as practicing sports outdoors.
• Yellow or orange: Filtering these colors increases the contrast. Therefore, it is recommended only on very cloudy or foggy days. They are inadvisable if there is a lot of sun.

2. UV filter

The most important feature of sunglasses is the filter for ultraviolet radiation. It is responsible for protecting us from the harmful effects of the sun, which, as occurs on the skin, also affects our eyes.

Depending on the wavelength, radiation is more or less harmful. Visible light is the light that the eye is capable of capturing and ranges from 400 to 800 nanometers. Radiation becomes dangerous when it is less than 400 nanometers (where we enter the ultraviolet spectrum). The glasses must ensure a radiation barrier below this figure, normally represented by the UV 400 logo. By law, all sunglasses should meet this requirement, hence the importance of the homologation when choosing the most appropriate glasses.

The ultraviolet filter has nothing to do with the color of the glass or with the glass being more or less dark. In fact, a transparent glass can have an ultraviolet filter that protects us from the harmful effects of the sun. What the dark glasses do is decrease the percentage of visible light that reaches our eyes, making it convenient to carry out a certain activity depending on the environmental conditions in which we find ourselves.

3. Visible light filter

Sunglasses are rated from 0 to 4 based on the filtering capacity of visible light, which is not the same as the filtering capacity of ultraviolet radiation, which is harmful to the eye, as has been explained above. The visible light filter determines whether the lens is comfortable or suitable for the environmental conditions in which it is used.

Depending on the absorption capacity of visible light, we have, according to ISO 8980-3, lenses in five categories:

• Category 0: clear glasses that absorb 0% to 19% light. They are indoor lenses, cloudy skies and can even be used at night.
• Category 1: lightly colored glasses that absorb between 20% and 56% of visible light. Moderate light conditions such as in urban areas.
• Category 2: slightly darker glasses that absorb 57% to 81% of visible light, suitable outdoors for medium sunlight conditions.
• Category 3: dark glasses that absorb between 82% and 92% of visible light. Suitable for strong light such as on the beach or in the mountains.
• Category 4: very dark glasses that absorb up to 96% -98% of visible light. Suitable for extreme solar luminosity such as that produced in high mountains or skiing, where in addition to direct light, account must be taken of the light reflected off surfaces such as water or snow.

Doctor Andrés Picó, ophthalmologist at the Barraquer Ophthalmology Center.