Generality
Polarized glasses are an eye-catcher that can neutralize glare and glare, generally coming from reflective surfaces, such as roads, lawns, beaches, water or snow.
Polarized lenses are equipped with a specific filter, called a polarizer, which allows linear light to pass through, but shields rays from other directions. By attenuating the reflected light, the polarized glasses allow a clearer and more defined vision, increasing, at the same time, the contrast and improving the perception of colors.
Polarizing filters reduce eye strain, as the view is not forced to compensate for glare and other phenomena resulting from reflected light.
Polarized glasses are particularly suitable for those who spend a very long time outdoors or practice activities, such as driving or sports, in which the eyes are more stressed and need more protection.
What are
Premise: what is meant by Polarization?
Natural light is not polarized, ie the electromagnetic waves that constitute it oscillate in every direction of three-dimensional space. When a sunbeam meets a smooth surface, such as a body of water or a ski slope, it undergoes a process called " polarization ", that is, it is partially reflected in a particular direction of propagation.
For example, sunlight reflected from a water surface or car windshields is horizontally polarized; wearing polarized glasses - whose polarization axis is orthogonal to the axis of the same reflections - the polarized light component is eliminated.
The POLARIZATION is, therefore, the capacity of the electromagnetic waves which constitute the light to modify its orientation, when these come into contact with the matter.
Simplifying further, we speak of POLARIZED LIGHT when light waves meet a flat surface, able to reflect them, that is they are addressed in a well defined direction. This change of axis and the resulting intense brightness cause glare, in turn responsible for:
- Reduced visibility ;
- Color distortion ;
- Fatigue and eye irritation .
The lenses of the polarized glasses have an optical filter (called polarizer or polarizing filter ) which:
- Passes a type of polarized light;
- Blocks waves of different polarization.
Eliminating about 99% of the reflection, the result is a clearer vision in specific situations and less fatiguing for the eye.
Polarized glasses: what are they?
Polarized glasses are devices on which ophthalmic lenses are fitted with an optical filter, called a polarizer, which neutralizes reflections from smooth and shiny surfaces such as water, sand, snow, grass lawns or asphalt.
To know
The polarizing filter (or polarizer) can be added to both sunglasses and eyeglasses.
When we talk about polarized glasses, therefore, we can refer to:
- Polarized glasses, that is corrective lenses (graduated) to which polarizing filters can be added, which act on visible radiations, modulating the brightness and eliminating glare. In this case, the lenses are generally dark (brown-brown) and, on the market, can also be defined as " graduated polarized sunglasses ";
- Polarized sunglasses, that is made up of sun lenses equipped with polarizers and sunscreens. In addition to limiting the phenomenon of glare, these lenses protect the eye structures from UV radiation. Polarized lenses attenuate the reflection more than traditional sun lenses.
Note : a pair of sunglasses is not associated with a polarizer by default. In fact, various filters (photochromatic, degrading, etc.) can be added to the lenses, which must be chosen according to one's needs; the most important variable to consider before buying is the absorption capacity of solar radiation (different depending on the light intensity of the environment in which you are).
How do they work
Basic concepts: what are ophthalmic lens filters?
- The ophthalmic lens essentially modifies the virginity of a radiation beam .
- The filters alter the energy composition of the light rays, preventing the passage of some wavelengths or limiting the energy of these.
- The lenses of the glasses can be filtering, when they change both the virginity and the energy characteristics.
How do Polarized Glasses work?
When the natural light (that is coming from the sun) hits the surface of the objects, a part of the radiations that constitute it is absorbed, while another part is reflected stimulating, through a series of processes, the eye and allowing:
- Vision ;
- Color perception ;
- Contrast sensitivity .
Considering the irregularities of the surface of the objects, the reflected radiations will not have a regular course. In practice, the reflected light will not reach the eye only perpendicularly, but laterally, obliquely and orthogonally .
The light that diffuses with linear orientation (that is, in the form of horizontal waves, perpendicular to the eye) is responsible for a clear vision and allows us to perceive colors and contrasts.
Non-linear light (from other directions) generates alterations in the quality of the images in the form of:
- Reflections ;
- Reverb ;
- Glare .
These phenomena compromise visibility, making it difficult to stay in the sun, drive, ride a bike, ski and do other activities.
The polarized glasses act by selecting the oscillating radiation along the polarization axis, thus blocking the waves of different polarization, responsible for disturbing phenomena for the vision.
Conventional (normal) ophthalmic lenses are made of materials whose molecules are randomly arranged. The particles that make up the polarizing filters, on the other hand, are intentionally aligned along the same plane: during the manufacture of the eyewear, the molecules are spaced between them based on the order of the wavelength of the incident light, forming a micro -network. The lenses will behave as partial polarizers, suppressing the part of radiation parallel to the plane of the molecules.
What are they for
Polarized glasses: what are they for?
Polarized glasses eliminate reflections that:
- They alter the perception of colors, contrasts and depth;
- They cause greater eye strain.
By canceling these effects, polarizing filter lenses improve vision, which is sharper and more comfortable, even in environmental conditions where the brightness is very intense. In fact, polarized glasses make it possible to avoid glare and glare and, at the same time, increase contrast, modulating lighting as needed. This results in a reduction in visual fatigue .
In the city, polarized glasses are very useful, but not fundamental, considering the fairly important cost. This type of lens is indicated, however, on more specific occasions: polarized glasses are almost indispensable for the welfare of the eyes in the high mountains, the sea, the beach or, more generally, when outdoor activities are practiced, where the reflection light is very intense. Suffice it to say that snow can reflect up to 85% of light rays, 20% water and 10% sand.
Reflections: disturbances that produce vision
Polarized glasses attenuate reflections in greater quantities than traditional lenses.
The horizontal reflections of the light alter the vision, creating unnatural contrasts, dazzling and tiring the view . On some surfaces, such as water, snow, sand and asphalt, these reflections can represent a danger: the rays circulate in an uncontrolled way and branch out in several directions, with the possibility of a real blinding effect .
Furthermore, the phenomena of reverberation and glare can:
- Decrease the contrast of the observed images with respect to the rest of the visual field;
- Create halos and light effects that are difficult to determine ("ghost" images);
- Make night vision difficult.
Polarized glasses: in which situations are they best suited?
The situations in which it is indicated to opt for polarized glasses are different.
The lenses equipped with these particular filters are particularly useful when driving (cars, motorcycles, bicycles) and in all activities that have to do with reflective surfaces, such as snow, ice, asphalt, sand, seas, lakes and rivers .
Polarized glasses can therefore be used outdoors, during sports - summer or winter - or recreational activities, where the vision can be "disturbed" by the presence of reflected light, such as:
- Cycling;
- Surf;
- Field hockey;
- Skiing;
- Fishing;
- Sailing.
How to choose Polarized Glasses
The lenses of polarized glasses can have different colors (so to speak, the color variations are similar to those of traditional sun lenses).
Each shade is indicated for a specific purpose.
At an indicative level, the options available are:
- Polarized brown lenses : they are probably the most versatile, since they allow you to see well, from morning until sunset, in various environmental situations;
- Gray polarized lenses : they are preferable in the presence of a direct and very intense light (as on clear days of full sun or when you go skiing in the snow), to keep the contrasts clean and defined;
- Pink polarized lenses : they are similar to the brown ones in the features, but they turn to a pinkish tint;
- Green polarized lenses : they are preferable in conditions of variable brightness, for example, when the weather is particularly changeable, that is to say passing from clear to cloudy sky very suddenly and several times over the same day. Polarized glasses with green lenses are also useful in cases where you switch from a bright light to a dimly lit area (eg mountain trekking).
If you spend a lot of time driving a vehicle or want more comfort during this activity, you should choose polarized glasses that also have a specific anti-glare treatment . The high-beam headlamps of the other cars, the illuminated signs or a too intense reverberation can be, in fact, a big source of distraction.
Advantages
What are the advantages of Polarized Glasses?
The polarized glasses have the characteristic of:
- Improve vision : polarized lenses eliminate glare and help to mitigate virtual perceptions (or ghost images) due to very intense light. As a result, the vision is sharp and comfortable, especially in very bright environments and open spaces. This characteristic of polarized glasses is to be taken into consideration in the practice of recreational or sporting activities (fishing, cycling, winter skiing, water sports, etc.) and in situations where it is necessary to increase safety, such as driving a car.
- Protect your eyes from UVA and UVB rays : as with the skin, excessive or irregular exposure to sunlight can be harmful to your eyes. Glasses with polarized lenses limit and prevent the harmful effects of this radiation.
- Increase visual comfort : by eliminating glare, the use of polarized glasses helps reduce fatigue, ensuring visual well-being.
- Ensuring better visual performance : by controlling the reflected light, the polarized glasses allow you to increase the contrast, making the image definition high. Polarized glasses offer greater continuity in the level of performance, as visual activity is less disturbed by dazzling effects.
Disadvantages
Polarized glasses: what are the disadvantages?
- While driving, the windshields of other cars may be subject to visual distortion . Being made of laminated glass, this part of the vehicles changes the polarization angle of the light, making the driver who is wearing the polarized glasses perceive a sort of grid . For some, this effect can be a source of discomfort or annoyance .
- Another dangerous situation that can arise when driving with the use of polarized glasses is the inability to see oil stains or icy areas on the road. The reflection they created could, in fact, be eliminated, making it difficult to detect them.
- Some visors of motorcycle helmets in combination with polarized glasses create rainbow light effects or let you perceive a dominant chromatic variation, such as, for example, violet.
- Another disadvantage is the higher cost, which makes polarized glasses less affordable than those with traditional lenses. This is justified by the particular manufacturing process of polarizing filters.
- The polarized glasses have some limitations, such as constraining the observation, at certain angles, of liquid crystal displays (LCD) or with TFT technology (Thin Film Transistor), of which they are equipped with mobile phones, computers, tablets, ebook readers and speedometers from bike. These screens transmit polarized light and have a rotation angle under which the lens of the glasses obscures the view (the screen appears completely black).
Tips
- Before buying a pair of polarized glasses, the first rule to remember is to avoid DIY and always ask the opinion of the ophthalmologist, who can indicate the type of lens that best suits your needs. The specialist can also assess the presence of specific contraindications that can interfere with the correct use of polarized glasses (and for example, can establish how long it is best to wear them or under what conditions it is best to avoid them).
- Purchase polarized glasses with the CE mark, bearing in mind that the frame must be comfortable and compatible with the type of lens chosen.
- To clean the lenses of the polarized glasses it is possible to opt for the use of microfibre cloths. These remove dust and moisture without scratching the glasses or leaving streaks. Instead, it is not advisable to use paper towels or shirt sleeves: these systems can damage the polarized glasses, as they collect debris and dust from the lenses by scratching them.
