We love to accessorize with sunglasses. They are great to complement a fashion composition with other accessories such as bags and watches. However, when choosing sunglasses you have to remember that they are not primarily related to fashion but to keep our eyes protected from intense light and from harmful Ultra-Violet radiation (UV-light). Sunglasses use advanced lenses that may include polarizing and UV filters.
Note that polarized lenses are not UV protective lenses. These two kinds of lenses work on different physical principles but they can be combined in the same sunglasses. For example, lenses can have a polarizing filter and also be covered by a UV protective film.
In short, polarizing lenses block reflected glare from bright surfaces and UV protective lenses block harmful Ultra-Violet light.
Polarizing lenses aim to block glare. UV protective lenses aim to block harmful Ultra-Violet light.
They avoid glare and increase visual comfort. This is special useful for people doing water sports, sailing or fishing willing to get rid of light reflections from the water surface.
The working of a polarizer is actually simple, you can imagine a horizontal rod being blocked by a vertical fence. Light if formed by electromagnetic waves that propagate with different orientations. Polarized light propagates in only on plane orientation. Polarized lenses are capable of blocking any polarized light that have a different angle than that of the of the lens in an analogous process to that of the horizontal rod stopped by the vertical fence. The light reflected by bright flat surfaces tend to be be polarized and consequently they can be totally or partially blocked by these special lenses.
Polarizing sunglasses have also drawbacks: they don’t block only polarized light caused by reflections coming from flat surfaces, they block any polarized light that don’t have the orientation of the filter. This includes polarized light coming from liquid crystal displays used in digital watches, smartphones, dashboards of cars, boats and planes and so on. A digital watch for instance may appear totally blank under a polarizer. Take this into account if you decide to purchase polarizing sunglasses. The extra visual comfort under high glare situations will also make it difficult or impossible to see information in liquid crystal displays. Note also that in some sports related to snow or sand you maybe interested in seeing the contrast of surface roughness and bumps which is enhanced by glare. Also in this cases, polarization may finish a drawback.
UV PROTECTIVE LENSES
Ultra-Violet light oscillates at a frequency higher than what our eyes can perceive. As a consequence, UV-light is invisible. We don’t see it but is out there and it is harmful both to our skin as well as to our eyes. The skin we protect with sun creams and the eyes we protect with UV-blocking lenses.
Sun creams have different UV protection levels and so do UV protection lenses. They are classified in grades such as UV1, UV2, UV3 etc. The higher the grade, the higher the UV blocking capability of the filter. However, higher UV grades also block more light (the lenses become darker and darker). Instead of buying a high grade UV lens it is better to buy what you really need, avoiding sunglasses unnecessarily too dark.
Check also: UV lenses classification
In summary, when choosing sunglasses with UV and polarizing filters, put health in first place and don’t look only for a design that matches your style. Assure also that your filters are appropriate for the intended use (activities like outdoor sports, high-mountain and beach require higher UV factor, casual or just for fashion purposes can have a lower UV index, water sports may feel better with addition of a polarizing filter). Buy from a reputable brand that assures high lens quality.