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Sunglasses (or sun glasses) are often colored or darkened glasses to protect the eyes from direct and annoying light and glare. Sunglass Sale Here!
Sunglasses mounts are usually made of metal or synthetic material, such as plastic or nylon. Lenses usually have different levels of ultraviolet (UV) blockage.
It is suggested the frequent use of sunglasses of good quality, that they fit the face so that protect them from the rays that come from the front and from the side, filtering properly, the UV rays can have harmful effects on eye health.
Brief History of Sunglasses
Sunglasses originated around the 12th century in China. It was the first place where a technology was developed to smoke quartz crystals with the aim of obscuring them. These smoked crystals were used by the Chinese judges and were not intended primarily to correct the view, nor to protect themselves from sunlight. The real purpose of the first sunglasses was to hide the expression of the eye during trials in order to hide any evidence of the final verdict that would only be given at the end of the trial.
In the mid-EIGHTEENTH century, the british James Ayscough began experimenting with tinted lenses. He did not conceive them as sunglasses or as a mechanism of protection against solar rays, but as a remedy to some specific problems of vision.
At the beginning of the 20th century, the use of sunglasses among the stars of the incipient silent cinema began to become widespread.
Sam Foster started mass production of economic sunglasses in the United States in 1929. In 1936 the first polarized glasses appeared
Sunglasses can be considered of three types:
In General They do not offer significant protection against the sun and are used as fashion accessories except of course the ones sol at this website.
- General purpose sunglasses
To reduce the glare of bright light.
- Special sunglasses
For activities such as skiing or for people very sensitive to glare.
Need for protection
Excessive exposure to ultraviolet radiation can cause short-and long-term eye problems, including photokeratitis, snow blindness, cataracts, and various eye cancers.Two
Special care should be taken with children under the age of 12, since until that age the lens is particularly transparent, which favours the absorption of UV radiation.
There is no proven correlation between high prices and increased UV 34 radiation protection a very dark lens color does not automatically guarantee that it filters UV light correctly. If this is not done, there is a particularly dangerous situation, as the dilated pupil, not receiving so much visible light, will receive even more UV radiation. In short, wearing sunglasses that do not properly filter UV rays can be more dangerous than not wearing sunglasses.
In the case of the vision of solar eclipses, the health authorities warn that the protection of sunglasses is insufficient for the direct vision of them.
Levels of protection
To date of writing this article (early 2008), attempts to define an international ISO standard have not been successful. In the absence of this, we can find three regulations on levels of protection:
Category EN 1836: transmittance:
4 from 3% to 8%
3 from 9 to 18%
2 from 19 to 43%
1 44 to 80%
0 80 to 100%
The European standard EN 1836: 2005 + A1: 2007 (UNE-EN 1836:2006+A1:2008 official Spanish version) establishes 5 levels that range, from minor to greater protection, from 0 to 4. In the European Union, it is important to demand that the eyeglasses display the CE5 mark as this ensures that they comply with this standard. Categories 2 and 3 are usually considered the best for average use, including driving. Category 4 is adapted to extreme uses, for example in snowy landscapes or water sports and is not suitable for driving (not even during the day).
The Australian standard AS 1067 also sets 5 levels of protection, ranging from 0 to 4.
The American standard ANSI Z80. 3-2001 does not distinguish between different levels of protection. It requires a transmittance of UVB (280 to 315nm) and UVA (315 to 380nm) not exceeding 1% and 50% respectively of the transmittance in the visible range.
Lenses may be made of glass or plastic material, specifically polycarbonate or a polymer called CR-39. Glass lenses have the best optical clarity and scratch resistance. Plastic lenses are lighter than glass lenses and are more resistant to impact breakage. Within the plastic lenses, the most commonly used material is CR-39.
The frames can be made of steel, plastic, wood, titanium or nitinol.
The color of the lens
The color of the lens may vary with fashion, but there are still a number of colors recommended for general uses and others for specific uses.
Green, grey or brown are recommended for general use. These minimize color distortions that would be dangerous in certain activities such as driving a car:
Grey lenses are considered neutral as they do not alter either the contrast or the colors. Especially recommended for driving.
Green or brown lenses can cause minimal color distortion and Increase Contrast. Especially recommended for outdoor sports.
By its distortion of the colors, relegated to specific uses:
Red lenses, good for medium or low lighting conditions, as they increase contrast.
Orange and yellow lenses are the best by increasing the contrast in depth perception on cloudy days. They are therefore used by golfers and hunters.
Blue or violet lenses, which have no real benefits. Its use is merely aesthetic.
Effect of a polarizer on the reflection in the mud. In the image on the left, the polarizer is turned to transmit the reflections. When the polarizer turns 90º (image on the right) almost all the reflected sunlight is blocked.
Sunlight does not reach the eye through a straight line, but from all possible directions. It becomes particularly “unpleasant ” when reflected on flat surfaces, as it causes visual fatigue and glare; basically it is an excess of light that removes visibility.
A polarized lens is a kind of vertical filter that blocks the sunlight that reaches the eyes horizontally, such as the one reflected in the sea, Snow, Road and asphalt, and allows the passage to the vertical light that can be used to clearly see.
If the lenses are polarized, the counterposing of two of them will not allow the passage of light.