When you decide to buy a pair of sunglasses you should keep in mind some fundamental aspects, one above all the quality of the lenses, this is because a good pair of glasses should be, even before an aesthetic accessory, a screen that protects our eyes from harmful sun rays.
Lenses and frame
There are two parts that make up the glasses: lenses and frames, the latter declined in many shapes, colors and materials and which often represents the aesthetic choice criterion for those who have to choose a new pair. The frames of sunglasses are very different from those used for eyeglasses and generally have thicker temples and a structure that covers the eye more, not to mention that they are manufactured with a greater amount of celluloid.
As for the lenses, a difference with eyeglasses is given by the fact that the lenses of the sunglasses are often enveloping lenses, considerably more curved and such as to follow the profile of the face, guaranteeing greater coverage.
Many sunglasses are fitted with lenses that, in addition to repairing the eye from radiation, allow the correction of visual defects, thus fulfilling the double task of eyeglasses and sunglasses. The materials with which modern sunglasses lenses are made are plastic or mineral resins or glass: if on the one hand the plastic is much more resistant to shocks, on the other hand the glass is more resistant to scratches. Glass is thinner but heavier, while plastic is thicker but lighter and has a lower refractive index.
Similarly to what happens for eyeglasses, various treatments such as anti-scratch and anti-reflective can be applied to sunglasses. The lenses are colored as they are treated in such a way as to obtain a reduction in the brightness that passes through them. When buying eyeglasses online, you should confirm the features first.
- Polarizing filter: when the light is reflected by water or snow, it is arranged on some oscillation planes. Polarizing filters are composed of spaced blades that prevent or attenuate the oscillation of light, precisely filtering the light reflections that come from reflective surfaces and thus allow for improved visibility.
- UV filter: filters ultraviolet radiation, which is very harmful to the eye, all without compromising brightness. The filtering level is indicated by the abbreviation “UV” followed by the maximum frequency of the filtered light, which is expressed in nanometers. UV400, for example, means the lens is treated to cut all ultraviolet frequencies down to 400nm.
- Colored filter: filters some particular frequencies (especially blue light) and is widely used for making ski goggles.
- Mirror: this is a treatment suitable for use in very strong light conditions, such as on snow and provides for a lens cover with a thin partially reflective layer.
Types of sunglasses
- Photochromic glasses: have lenses with variable color depending on the external brightness.
- Degrading glasses: they have a variable color and consequently a variable transmission of brightness on the lens: in particular the upper part acts as a screen against solar radiation, while the lower one is more transparent. It is a type suitable for driving vehicles.
Tips for buying
Excessive exposure to UV rays can cause a variety of eye problems, such as burns, cataracts and even cancers. This is why it is important to choose a quality model that allows effective protection, even in very strong light conditions, such as that which occurs in the presence of snow or ice, highly reflective elements. A great pair of sunglasses should block at least 99% of UVB rays and at least 95% of UVA rays.
It is strongly not recommended to purchase models that do not have any labels containing the lens type information.
Absolutely avoid all those sunglasses sold in stalls at bargain prices or without packaging and / or labels. The regulations require that each model be accompanied by certain information about the manufacturer and the type of filter. In the absence of this information, it is advisable to refrain from purchasing. You should, for example, buy trendy eyeglasses from a reputable seller.
It is important to make sure you buy glasses that are the right size and fit the size of your face. Before proceeding with the purchase, try them on carefully, making sure they do not bother in any way. The weight should be evenly distributed between the ears and nose, and the lashes should not touch the frame or the lenses.