What are polarized sunglasses? The secret is in their polarized crystals?
A polarized sunglasses is a base sun lens to which is added a special sheet that only blocks the light coming in a certain direction.
The usual thing is that in the case of sunglasses are vertically polarized, so that it will fundamentally block the light that comes horizontally.
Based on the fact that the sunlight is not polarized (vibrates in all directions), the glasses can not simply block it but what happens is that when that light is reflected on a horizontal surface (the road; especially if it is wet, water, a glass, etc ...), then the lens does block it.
When using polarized sunglasses the glare produced by the sun reflected on the surface is reduced dramatically and improving the vision. They are manufactured for both neutral and graduated sunglasses.
What are the advantages of polarized sunglasses?
Polarized sunglasses are especially interesting for certain types of outdoor activities such as driving, fishing, water sports and snow, but also benefit us in many other situations.
You can also see that the areas in shade do not darken as much as with the "normal" sunglasses so when passing through shaded areas or even tunnels the vision is achieved is better.
This effect also makes it possible to see better if we look at the bottom of a river on a bright day because it removes the reflection that gives the water. To such an extent this is true that in fishing competitions the use of polarized glasses is strictly forbidden, since they would give a considerable advantage over the other participants in being able to see the bottom fish much better.
As a curiosity I will also tell you that polarized (not sun) lenses are also used in films in three dimensions using films positioned in different directions in both eyes. Some of the light reflected from the screen is polarized vertically while the other is polarized horizontally. This means that each of the lenses will filter one type of wave and not the other, resulting in 3-dimensional sensation if the film is projected in that format. The viewer's brain takes both images and combines them to create a realistic sense of depth.
Nowadays already exist in the market filters polarized of different grades reason why it is possible to choose depending on the use a greater or less protection and to combine all this with filters and treatments antireflecting.
Disadvantages of polarized sunglasses
In my opinion they are very few but you have to keep them in mind. We must bear in mind that the polarized lenses of sunglasses do not offer protection for all glare. If the user tilts his head more than 45 degrees, some horizontal light reflections can enter and cause some bright spots. Some users who wear polarized lenses in their sunglasses in snowy areas, notice that they lose some contrast between the snow.
This same problem can happen when polarized glasses and devices with LCD screens (computers, navigators, mobile phones) are used because they can distort the images in certain viewing positions and even make the screens look very dark.