How to choose quality sunglasses. How to choose the right sunglasses? Which lenses do you prefer?

So that they protect the eyes, fit correctly, and do not break a week after purchase. Their purchase should be taken responsibly, since counterfeit glasses not only do not provide protective effects, but also contribute to the deterioration of vision. If in Russian realities a fake RayBan is quite suitable for the season, then in Thailand it is better to choose quality over price.

Frame and lens material

First, pay attention to the lenses. Which lenses for sunglasses to choose? nature itself suggests - the glass that fashionistas are chasing is less scratched, but only partially blocks ultraviolet radiation. But high-quality polymers, like polycarbonate, prevent rays A and B from reaching the retina. Infrared rays only block polarized sunglasses, and classics, especially fashion ones, do not hinder them at all.

Advice! If you have to drive a car often, then it is best to leave your choice on plastic glasses, as they are safer in case of a possible accident (what to do if?). Such glass will either simply fly out of the frame, or even if it breaks, the risk of injury is minimized.

The frame material can be any. Lightweight plastic has its advantages, for example, it is durable and lasts a long time. Metal models with wooden inserts look no less stylish, and they are stronger than plastic. It’s just important to carefully consider the places where the lenses are attached to the frame; if the metal frame is overtightened, cracks can form at the fixation points, they dramatically spoil the appearance of the accessory and reduce its service life.

Glass color and tint level

Not all sunglasses are ideally dark. The barrier to sunlight is not the intense coloring of the lenses. Even, on the contrary, extremely dark lenses without a protective filter against ultraviolet radiation harm the eyes even more than translucent “chameleon” glasses. The fact is that behind dark lenses, the pupil involuntarily expands and literally absorbs harmful rays.

Radiation protection

If you still can't decide, then try choose sunglasses by type of protection. Manufacturers indicate the barrier indicator and type of filter on a special insert included with the accessory. Additionally, some manufacturers mark on the insert the conditions in which it is recommended to use the glasses.

• “0” – minimal protection from all types of radiation, the filter transmits at least 80% of light.
• “1” and “2” – categories of average radiation protection. The first category transmits from 43 to 80 percent of light, and the second - 18–43 percent.
• “3” is an excellent solution for relaxation and living by the sea, visits to nature and daytime city walks. Glass filters transmit no more than 18% of light.
• “4” – glasses for Thailand, a place where the sun does not spare either the eyes or the skin (). Their light transmission is 3–8 percent.

You can choose sunglasses to suit your face, but do not forget about light transmission, it should be level 3 or 4 for eye comfort in Thailand.

Polarizing coating

Choose the right sunglasses Understanding all their characteristics will help. Optical store salespeople often mention polarization when talking about eyewear models for car enthusiasts and beach lovers. Essentially, the presence of a polarizing filter indicates that the lenses have a special coating applied to them to block glare and reflections. Therefore, for those who have decided choose quality sunglasses To stay at resorts in Thailand, you need to pay attention to models with good polarization. Scientifically speaking, such a filter cuts off the peaks of the amplitudes of light waves that exceed a given norm.

How to check polarized glasses when purchasing?

There are three methods known to us.

1. Hologram. Look at the hologram, indistinguishable without glasses; stores usually have them. Just ask the seller for it.
2. Smartphone. Turn on the display to maximum brightness and set a white background, bring polarized glasses to your eyes and turn them vertically 90°, the lenses should darken to complete opacity.
3. Two in one. Put on the glasses, bring the second (same) ones at a distance of 10-15 cm from the first and slowly turn them to an angle of 90°. The lenses should darken completely; if partial transparency remains, then the filter in one of the glasses is not 100% polarizing.

Advice! Leave your choice on polarized glasses, since ordinary ones will not be able to protect your eyes as effectively as those described above.

Photochromic coating

The photochromic layer turns ordinary lenses into “chameleons”. Depending on the lighting, the percentage of light rays transmitted photochromic sunglasses changes, allowing them to be used even at night for driving a car. This filter works as follows: when light hits the glasses with a photochromic filter, they begin to darken, therefore, at night, the glasses become transparent.

Choosing sunglasses to suit your face

The simplest answer to the question is how to choose sunglasses according to your face shape, this is advice to try on the model you like. But sometimes there is no time to try on the entire assortment of the store, or you plan to order an accessory on the Internet, which eliminates the possibility of putting them on and going to the mirror. In this case, stylists have created a series of recommendations that will help choose the right shape of sunglasses, focusing only on facial type and features. But first, let's look at some practical advice from professionals.

What does the label tell us...

The edges of the glasses frames should protrude slightly beyond the boundaries of the face. But they should not be wider than 1.5 cm. On a wide face, massive frames will look heavy, but those with an elongated head shape should choose options that will protrude slightly at the temples, thereby adjusting the width of the cheekbones. The thickness of the frame is a matter of taste, but sometimes it also indicates which sunglasses to choose. So, those with fine features (narrow lips and bridge of the nose) should not get carried away with models decorated with a scattering of stones. In turn, models without frames will clearly lose against the background of plump lips and a wide snub nose.

Which glasses suit your face shape?

Round face type. When the widest area is the cheeks, and the height is almost equal to the width of the face, you need to try to visually lengthen it with glasses. Models with square or rectangular lenses are suitable for this. It is important that the corners are rounded and the frame is clearly distinguished by color, then the desired effect will be achieved.

Square face type. The angularity of the forehead and jaw indicates that glasses should smooth out this geometry. The frame in this case should be indirect, slightly rounded along the top line. Massive frames will fit perfectly, but it is important not to overdo it, otherwise the accessory will, on the contrary, emphasize what needs to be hidden.

Triangular face type. High cheekbones and a sharp chin are the main signs of a triangular face shape. In this case, the glasses should balance the heavy top and narrow bottom. To do this, take a closer look at them, the shape of the lenses is called “cat’s eye”; models with oval lenses, slightly narrowed downward, are also suitable.

Oval face type. This is the case when you can decide on any experiments. Owners of this face shape will suit both square and round frames of any thickness and type.

Oblong face type. This type requires glasses that widen the cheekbones. Large glasses with soft frame lines have this feature. It’s great if the top line of the frame is different in color, this will smooth out the lack of pronounced cheekbones and cheekbones.

Video: in addition to the post on choosing glasses

The lenses in Polaroid and INVU glasses are labeled UV-400 or 100% UV-Protection, guaranteeing 100% UV protection. Let's tell you in more detail how it works.

Ultraviolet radiation poses a danger to human eyes: UVA waves are responsible for premature aging of the eyes, UVB can cause irritation of the cornea, UVC are carcinogenic and can damage cell membranes and cause mutations.

The effects of ultraviolet radiation on the eyes are most often cumulative. If you neglect to protect your eyes from harmful radiation for many years, this significantly increases the risk of cataracts and cancer. But there are circumstances in which exposure to ultraviolet light in a matter of days or even hours affects the health of the eyes. For example, many of you have heard about such a disease as “snow blindness” - this is a burn injury to the eye, which often develops in people exposed to ultraviolet radiation reflected from the snow surface - skiers, climbers, polar explorers, winter fishing enthusiasts, etc.

The easiest way to protect your eyes from UV rays is to wear quality sunglasses. But how not to make a mistake when choosing them?

Myths about UV protection glasses:

1. Sunglasses with clear lenses do not protect your eyes.

This is wrong. Untinted glasses can also be excellent eye protection. The fact is that ultraviolet protection is provided by additional coatings or layers in the lens body. And the darkening layer is only responsible for reducing the brightness of the light.

2. D Even non-brand glasses do not protect against ultraviolet radiation.

Let's be honest, numerous professional and amateur tests, publications about which can be found both on the Internet and in various media, have shown that, most often, both Chinese fakes "from the transition" and branded glasses cope equally with ultraviolet protection from official stores.

Does it make sense in this case to buy more expensive sunglasses? This is everyone's personal choice. Obviously, buying items of dubious manufacture is always a risk. Thus, with low-quality sunglasses, there is a risk that their lenses may not have UV protection, or it may be provided by a coating that will quickly wear off during use. In addition, such glasses will be significantly inferior to branded ones in many other respects.

3. Glass lenses protect your eyes better than plastic ones

This really was true, but many decades ago. Thanks to modern technologies, high-quality plastic lenses are not inferior to glass ones in terms of UV protection. Let's say more - modern plastic lenses are much better than glass ones if we evaluate them from the point of view of convenience, durability and safety. Glass lenses are quite heavy in weight and are very easy to break with the slightest impact, and the fragments from them can injure you. Plastic makes it possible to produce the thinnest, almost weightless lenses with various inclusions to protect against ultraviolet radiation, eliminate glare, increase the strength of lenses and protect them from scratches.

Read the label: UV-400

A proven brand and the inscription on the label “UV-400” guarantee 100% eye protection from ultraviolet radiation. You can also find the spelling 100% UV-Protection or 100% UV protection. This means that the lenses provide eye protection from all ultraviolet radiation with a wavelength of less than 400 nm - that is, from UVA, UVB and UVС rays.

There is also a standard "UV-380" - the presence of this marking means that the lenses block light waves with a length of less than 380 nm. According to most experts, glasses labeled UV-380 provide only 90% eye protection from harmful influences, and only a few experts are inclined to claim that this degree of protection is sufficient for eye health.

The degree of sunlight transmission and the level of protection from ultraviolet rays are two key indicators that determine the quality and scope of a particular model of sunglasses. So, let's look at how to choose sunglasses by type of protection.

Sunglasses protection level

There are four levels of sunglass protection in total. Level “0” means that such glasses can only be worn in cloudy or cloudy weather, since they transmit from 80% to 100% of the sun’s rays. "1" is suitable for low sun, such as a summer evening. The degree of transmission of rays by lenses with such markings is 43 – 80%. Glasses marked “2” are suitable for strong sun and can be chosen if you decide to spend the summer in the city. They block most of the sunlight, transmitting from 18% to 43% of the rays to the eye. “3” is suitable for relaxing by the sea, where the sun is already very intense. The transmission percentage in them is only 8–18%. The most secure glasses have level “4”. In such lenses, your eyes will be comfortable even in the sun, since they transmit from 3% to 8% of the sun's rays.

Information about what kind of protection sunglasses should have should be looked at on the label, which also contains information about the manufacturer. Any high-quality model should have such labels. In addition, it is worth paying attention to the fact that the higher the protection, the darker the lens. Thus, glasses with protection level “4” cannot even be used when driving a car, they are so dark.

Sunglasses with UV protection

How to determine the protection level of women's sunglasses, in addition to information about light transmission? For this purpose, there is another parameter on the label - data on how many ultraviolet rays (UVA and UVB spectrum) this or that model transmits. There are three types of glasses depending on this parameter:

1. Cosmetic– such glasses practically do not block harmful radiation (transmission rate is 80–100%), which means they can be worn when the sun is not active.
2. General– glasses with this marking are perfect for use in the city, since their glasses reflect up to 70% of the radiation of both harmful spectra.
3. Finally, for a holiday by the sea or in the mountains you need to select glasses with the marking High UV protection, since they reliably block all harmful radiation, which multiplies many times when reflected from water.

Summer is just around the corner, and that means it’s time to seriously think about protection from the sun’s rays. You need to protect not only your skin, but also your eyes.

The optimal protection for your eyes from the bright sun is sunglasses. How to choose them correctly?

Today it is a question not so much of aesthetics, but, first of all, of health. After all, even the name of this current spring-summer accessory says: its main function is to protect the eyes and the skin around them from the harmful effects of ultraviolet rays.

Any fashion trends and designer frames are not the most compelling argument when choosing sunglasses if you even think a little about the health of your eyes. Much more important are the technical characteristics of sun protection optics, which allow you to protect your eyes from the destructive effects of the sun.

In extreme eye conditions - for example, on a bright day or on mountain slopes, poor-quality glasses can cause irreparable damage to your vision, including central eye degeneration and cataracts. The sun's rays pose a particular danger to older people, since the amount of melanin pigment, which protects the eyes, decreases with age. Therefore, for pensioners who no longer think about fashion, sunglasses are vital.

What to look for when choosing glasses? If you don’t want to delve into the intricacies of your choice, buy branded sunglasses. Brands care about their image, so they do not produce a product that is hazardous to health. In general, high-quality glasses imply not only stylishness and vision protection, but also ensuring image clarity with the ability to change its brightness without changing color rendition.

Reasons for wearing

Here are some compelling arguments given by ophthalmologists and physicists who strongly recommend not leaving your eyes unprotected:

Serious and sometimes irreversible damage to the organs of vision from UV rays can appear five hours after active exposure to the sun on the eyes. The most dangerous consequences of UV irradiation are the occurrence of cataracts, burns of the cornea of ​​the eye, and partial loss of vision.

If, after spending a day in the sun without sunglasses, you notice watery eyes, painful sensations in your eyes in bright light, or blurred vision, then most likely your eyes have been attacked by UV radiation and have lost the battle. The most reasonable thing in this situation is to immediately run for a consultation with an ophthalmologist.

Exposure to ultraviolet radiation is always dangerous for the human eye. UV waves, even in small doses, will not benefit the eyes; they are always a damaging factor.

Active exposure to ultraviolet radiation causes photokeratitis - a sunburn of the cornea of ​​the eye, which can lead to temporary loss of vision. Previously, this phenomenon was often observed among polar explorers or skiers, which is why ophthalmologists call it “snow blindness.” Today, photokeratitis most often affects those who vacation at equatorial resorts and do not wear sunglasses. Remember: the closer to the equator you are, the more intense your eyes will be exposed to UV rays. Another rule is that the higher you go in the mountains or closer to the water, the more aggressive the UV radiation behaves. This means that the more you need sunglasses.

It turns out that even cloudy weather is not a reason to stop wearing sunglasses. Experts say that enough ultraviolet rays pass through clouds that are harmful to the eyes.

Which lenses do you prefer?

So, the benefits of wearing sunglasses are obvious. The question remains - how to choose not just a beautiful accessory, but also reliable protection?

It turns out that darkened glasses lenses do not always indicate UV protection. Most sunglasses with plastic lenses are cheap replicas of a well-known brand, or even dangerous fakes. They transmit up to 100% of UV rays, even being “blacker than black”. Moreover, the blacker such glasses are, the more dangerous they are! In bright light, the pupil of the eye contracts to reduce the risk of potential burns - this natural protection from UV radiation is provided to us by nature. And in cheap dark glasses without ultraviolet filters, the pupil remains “deceived.” It does not narrow, taking on the full extent of the sun's impact.

When choosing the right sunglasses, it is important to know a few nuances. The first and most important point is the material from which the lenses are made. There are few options - lenses are made of either glass or plastic. Each material has advantages and disadvantages.

Plastic lenses

Their advantage is that plastic glasses are difficult to break - they do not crumble into dangerous fragments, but turn into cobweb crumbs, safe for the eyes and skin. Plastic lenses are also lightweight, and such glasses are much lighter compared to glass ones.

But here is a significant disadvantage - any plastic transmits 100% of ultraviolet radiation. Thus, the safety criterion for plastic lenses consists only of the quality of the material and filters that are used to create the blocking layer on the glasses.

Another drawback: plastic lenses are easily scratched. Carrying them in a purse without a case is like scratching them with your own hands with a knife. Additionally, extreme heat can warp the plastic.

Glass lenses

It would seem that glass has more advantages than disadvantages. Indeed, unlike plastic, glass does not transmit ultraviolet radiation, even if the lenses themselves are transparent. You can choose glasses with minimal darkening and be calm about the health of your eyes. Another advantage of glass sunglasses is that glass lenses are less likely to scratch.

But there are also disadvantages. Glass is a dangerous material, especially in such close proximity to the eyes. If you like active sports or drive a car, then it’s better not to think about glass lenses, the risk is too great.

The choice with maximum protection

Today plastic lenses are very popular. Depending on the amount of ultraviolet rays transmitted, they are conventionally divided into classes in sunglasses:

Cosmetic
Marking on labels - Cosmetic. These lenses can be classified more as aesthetic than actually safe for health - they transmit from 51 to 100% of UV rays. It makes sense to choose them only during the season when the sun is inactive.

Universal
Marking - General. Ophthalmologists claim that this category of lenses is ideal for the Russian climate. Such lenses transmit less than half of the dangerous radiation, 20-50%. Sunglasses of this class are suitable for wearing in the city, where a large stream of sunlight does not reach the ground.

Special
Marking - High UV-protection. These lenses reliably protect the retina from burns. These sunglasses will be simply indispensable on vacation, especially on the ski slopes, where snow increases the amount of sunlight.

What does the label say?

High-quality sunglasses have special markings that help you make the right choice depending on your needs. Information about what class the lenses belong to is usually available on the label. But it is mandatory that it is indicated in the certificate for sunglasses. The level of protection is indicated in the inserts supplied with the glasses. They also contain information about the conditions in which the glasses are recommended for use (mountains, water surface, city, etc.).

— «0» - light transmission 80-100 percent. Minimum protection against all types of ultraviolet radiation.
— "1", "2"- light transmission, respectively, 43-80 percent and 18-43 percent. These glasses are recommended for use in urban environments, since they only partially protect against ultraviolet radiation.
— "3"- light transmission 8-18 percent. This type of glasses can be chosen for regular beach holidays and outdoor trips.
— "4"- light transmission 3-8 percent. This is a very dark filter designed for high altitudes and hot countries.

Most often the inscription says the following: “Blocks at least 80% UVB and 55% UVA.” This means that the lenses block 80% of UVB and 55% of UVA.

You don't need to worry about the intricacies of distinguishing between UV waves of different lengths - any UV waves are dangerous for the eyes.

Something else needs to be taken into account - the higher the percentage, the better eye protection you get. Ophthalmologists advise choosing sunglasses in which both indicators are more than 50 percent.

Color is important too!

For relaxing on the beach or sailing, glasses with polarized lenses are ideal, which, in addition to ultraviolet radiation, will neutralize glare on the water. Their color should be dark green or gray.

It is better to relax in the mountains and ski in gray or brown glasses with a mirror coating.

Polarizing filters don't let you see intense light reflection from surfaces (wet asphalt, snow, ice, water), leading to poor visibility. By cutting off the harmful part of the “light”, they provide more comfortable and clear vision.

Photochromic lenses capable of responding to ultraviolet radiation by changing the amount of transmitted light. They are used in so-called chameleon glasses, which darken in the sun, and in the absence of sunlight their lenses become transparent.

When choosing sunglasses with photochromic lenses, consider darkening speed and lightening speed, as well as temperature sensitivity.
By the way, photochromic agents - special substances used in the production of such lenses - are more active at low temperatures. That is, in the heat, the darkening of photochromic lenses is less, and the eyes are less protected by them.
Over time, the photochromic agents in the lenses may wear out and the lens darkening will weaken. Therefore, such glasses must be regularly replaced with new ones.

It would seem that the darker the glasses, the better they should protect the eyes. But intensely colored lenses are not always able to block solar radiation.

If the lenses just painted and do not have UV protection properties, its dose is even greater than that received through a transparent lens. After all, the pupils dilate behind dark lenses. Therefore, poor-quality sunglasses contribute to greater eye damage from ultraviolet radiation.

How to choose glasses?

Let's summarize what you should pay attention to when choosing glasses...

1. Decide in advance what you need sunglasses for.
2. If you have vision problems or eye diseases, be sure to consult an ophthalmologist before choosing sunglasses.
3. Do not buy sunglasses from stalls and markets. Quality glasses don't have to be expensive. Choose from those sold in stores, such as tourist shops, that have clear labeling and inserts.
4. Carefully study the labeling of glasses - it indicates how much ultraviolet rays the lenses of the glasses transmit, whether they are able to adapt to the brightness of the light or remove glare.
5. If you drive a car or often go out into the sun and back, buy glasses with photochromic lenses. To relax in the snowy mountains, it is better to purchase glasses with polarized lenses.

The most correct size glasses with large lenses that make a person look like a dragonfly or a skier. Such models protect not only the eyes, but also the skin of the face, on which “crow’s feet” form from ultraviolet radiation. Small glasses that do not cover your eyes well are of little use.

And you also need to remember - even with the most reliable glasses, you should not look directly at the sun. Wear high-quality sunglasses - and you will not only be elegant, but also healthy!
Based on materials from www.km.ru, www.takzdorovo.ru

You can't see, hear, or feel ultraviolet radiation, but you can actually feel its effects on your body, including your eyes.

You probably know that excessive ultraviolet exposure increases the risk of skin cancer, and you try to use protective creams. What do you know about protecting your eyes from UV radiation?
Many publications in professional publications are devoted to the study of the effects of ultraviolet radiation on the eyes, and from them, in particular, it follows that long-term exposure to it can cause a number of diseases. In the context of a decrease in the ozone layer of the atmosphere, the need for the correct selection of means of protecting the organs of vision from excess solar radiation, including its ultraviolet component, is extremely urgent.

What is ultraviolet?

Ultraviolet radiation is electromagnetic radiation invisible to the eye, occupying the spectral region between visible and X-ray radiation within the wavelength range of 100-380 nanometers. The entire region of ultraviolet radiation (or UV) is conventionally divided into near (l = 200-380 nm) and far, or vacuum (l = 100-200 nm); Moreover, the latter name is due to the fact that the radiation of this area is strongly absorbed by air and is studied using vacuum spectral instruments.

Rice. 1. Full electromagnetic spectrum of solar radiation

The main source of ultraviolet radiation is the Sun, although some sources of artificial lighting also have an ultraviolet component in their spectrum; in addition, it also occurs during gas welding work. The near range of UV rays, in turn, is divided into three components - UVA, UVB and UVC, which differ in their effect on the human body.

When exposed to living organisms, ultraviolet radiation is absorbed by the upper layers of plant tissue or the skin of humans and animals. Its biological action is based on chemical changes in biopolymer molecules caused both by their direct absorption of radiation quanta and, to a lesser extent, by interaction with the radicals of water and other low-molecular compounds formed during irradiation.

UVC is the shortest wavelength and highest energy ultraviolet radiation with a wavelength range from 200 to 280 nm. Regular exposure of living tissue to this radiation can be quite destructive, but fortunately it is absorbed by the ozone layer of the atmosphere. It should be taken into account that it is this radiation that is generated by bactericidal ultraviolet radiation sources and occurs during welding.

UVB covers the wavelength range from 280 to 315 nm and is medium-energy radiation that is hazardous to human vision. It is UVB rays that contribute to tanning, photokeratitis, and in extreme cases, cause a number of skin diseases. UVB radiation is almost completely absorbed by the cornea, but some of it, in the range of 300-315 nm, can penetrate the internal structures of the eye.

UVA is the longest wavelength and least energetic component of UV radiation with l = 315-380 nm. The cornea absorbs some UVA radiation, but most of it is absorbed by the lens. This is the component that ophthalmologists and optometrists should primarily take into account, because it is the component that penetrates deeper into the eyes than others and is potentially dangerous.

The eyes are exposed to a fairly wide range of UV radiation. Its short-wavelength part is absorbed by the cornea, which can be damaged by prolonged exposure to radiation waves with l = 290-310 nm. As ultraviolet wavelengths increase, the depth of its penetration into the eye increases, and most of this radiation is absorbed by the lens.

The lens of the human eye is an excellent filter created by nature to protect the internal structures of the eye. It absorbs UV radiation in the range of 300 to 400 nm, protecting the retina from exposure to potentially harmful wavelengths. However, with long-term regular exposure to ultraviolet radiation, damage to the lens itself develops; over the years, it becomes yellow-brown, cloudy and, in general, unsuitable for functioning for its intended purpose (that is, cataracts form). In this case, cataract surgery is prescribed.

Light transmission of spectacle lens materials in the UV range.

Eye protection is traditionally done with the use of sunglasses, clips, shields, and hats with visors. The ability of spectacle lenses to filter out potentially dangerous components of the solar spectrum is associated with the phenomena of absorption, polarization or reflection of the radiation flux. Special organic or inorganic materials are introduced into the material of spectacle lenses or applied as coatings to their surface. The degree of protection of spectacle lenses in the UV region cannot be determined visually based on the shade or color of the spectacle lens.

Rice. 2. Ultraviolet spectrum

Although the spectral properties of spectacle lens materials are regularly discussed on the pages of professional publications, including Veko magazine, there are still persistent misconceptions about their transparency in the UV range. These incorrect judgments and ideas are expressed in the opinions of some ophthalmologists and even spill out onto the pages of mass publications. Thus, in the article “Sunglasses can provoke aggressiveness” by consultant ophthalmologist Galina Orlova, published in the St. Petersburg Vedomosti newspaper on May 23, 2002, we read: “Quartz glass does not transmit ultraviolet rays, even if it is not darkened. Therefore, any glasses with glass spectacle lenses will protect your eyes from ultraviolet radiation.” It should be noted that this is absolutely false, since quartz is one of the most transparent materials in the UV range, and quartz cuvettes are widely used to study the spectral properties of substances in the ultraviolet region of the spectrum. In the same place: “Not all plastic eyeglass lenses will protect against ultraviolet radiation.” We can agree with this statement.

In order to finally clarify this issue, let us consider the light transmission of basic optical materials in the ultraviolet region. It is known that the optical properties of substances in the UV region of the spectrum differ significantly from those in the visible region. A characteristic feature is a decrease in transparency with decreasing wavelength, that is, an increase in the absorption coefficient of most materials that are transparent in the visible region. For example, ordinary (non-spectacle) mineral glass is transparent at wavelengths above 320 nm, and materials such as uviol glass, sapphire, magnesium fluoride, quartz, fluorite, lithium fluoride are transparent in the shorter wavelength region [BSE].

Rice. 3. Light transmission of spectacle lenses made of various materials
1 - crown glass; 2, 4 - polycarbonate; 3 - CR-39 with light stabilizer; 5 - CR-39 with a UV absorber in the polymer mass

In order to understand the effectiveness of protection from UV radiation of various optical materials, let us turn to the spectral light transmission curves of some of them. In Fig. the light transmission in the wavelength range from 200 to 400 nm is presented for five spectacle lenses made of various materials: mineral (crown) glass, CR-39 and polycarbonate. As can be seen from the graph (curve 1), most mineral spectacle lenses made of crown glass, depending on the thickness at the center, begin to transmit ultraviolet light at wavelengths of 280-295 nm, reaching 80-90% light transmission at a wavelength of 340 nm. At the border of the UV range (380 nm), the light absorption of mineral spectacle lenses is only 9% (see table).

This means that mineral spectacle lenses made from ordinary crown glass are unsuitable for reliable protection against UV radiation unless special additives are added to the batch for glass production. Crown glass spectacle lenses can only be used as sun filters after applying high-quality vacuum coatings.

The light transmission of CR-39 (curve 3) corresponds to the characteristics of traditional plastics that have been used for many years in the production of spectacle lenses. Such spectacle lenses contain a small amount of light stabilizer that prevents photodestruction of the polymer under the influence of ultraviolet radiation and atmospheric oxygen. Traditional spectacle lenses made of CR-39 are transparent to UV radiation from 350 nm (curve 3), and their light absorption at the boundary of the UV range is 55% (see table).

We would like to draw the attention of our readers to how much better traditional plastics are in terms of UV protection compared to mineral glass.

If a special UV absorber is added to the reaction mixture, then the spectacle lens transmits radiation with a wavelength of 400 nm and is an excellent means of protection against ultraviolet radiation (curve 5). Spectacle lenses made of polycarbonate are distinguished by high physical and mechanical properties, but in the absence of UV absorbers they begin to transmit ultraviolet radiation at 290 nm (that is, similar to crown glass), reaching 86% light transmission at the boundary of the UV region (curve 2), which makes them unsuitable for use as a UV protection agent. With the introduction of a UV absorber, spectacle lenses cut off ultraviolet radiation down to 380 nm (curve 4). In table 1 also shows the light transmission values ​​of modern organic spectacle lenses made of various materials - highly refractive and with average refractive index values. All these spectacle lenses transmit light radiation starting only from the edge of the UV range - 380 nm, and reach 90% light transmission at 400 nm.

It must be taken into account that a number of characteristics of spectacle lenses and design features of frames affect the effectiveness of their use as means of UV protection. The degree of protection increases with increasing area of ​​the spectacle lenses - for example, a spectacle lens with an area of ​​13 cm2 provides 60-65% degree of protection, and with an area of ​​20 cm2 - 96% or even more. This occurs by reducing side illumination and the possibility of UV radiation entering the eyes due to diffraction at the edges of spectacle lenses. The presence of side shields and wide temples, as well as the choice of a more curved frame shape that matches the curvature of the face, also contribute to increasing the protective properties of glasses. You should be aware that the degree of protection decreases with increasing vertex distance, since the possibility of rays penetrating under the frame and, accordingly, getting into the eyes increases.

Cutting limit

If the cutoff of the ultraviolet region corresponds to a wavelength of 380 nm (that is, light transmission at this wavelength is no more than 1%), then why do many branded sunglasses and spectacle lenses indicate a cutoff of up to 400 nm? Some experts argue that this is a marketing technique, since providing protection above the minimum requirements is more popular with buyers, and the “round” number 400 is remembered better than 380. At the same time, data has appeared in the literature about the potentially dangerous effects of light in the blue visible region spectrum to the eye, which is why some manufacturers have set a slightly larger limit of 400 nm. However, you can rest assured that 380 nm protection will provide you with sufficient UV protection to meet today's standards.

I would like to believe that we have finally convinced everyone that ordinary mineral spectacle lenses, and even more so quartz glass, are significantly inferior to organic lenses in terms of ultraviolet cutting efficiency.

Prepared by Olga Shcherbakova, Veko 7/2002