UV hazards today
The thinning of the ozone layer increases the amount of UV radiation that reaches the earth. For every percent that the ozone layer becomes thinner, the amount of UVB rays reaching the earth increases by 2%. At higher altitudes, exposure to UV rays is higher, as 85% of UV rays are reflected on snow and light-colored sand.
There is a possibility that too much UV exposure could result in macular degeneration . The impact of UV light on the health of our eyes is a major concern. Several countries have set voluntary or (in the case of Australia) mandatory sunglasses standards to provide maximum protection for their residents’ eyes.
Two kinds of UV
- UVA rays (the “aging” sun rays) promote the early appearance of wrinkles and cataracts . Their wavelength is closest to visible light, and they travel through water, glass, clouds and some clothing.
- UVB rays are the rays that burn the skin, they cause skin cancers and snow blindness. These rays are more intense during the summer months.
Glare, dazzling light
Bright flashes from water or shiny surfaces can strain the eyes with 10-12 times more light than they need to see. It can be painful and a dangerous distraction while driving or exercising. To make sure that sunglass lenses block the glare, try them on in front of a mirror. If you can still see your eyes, the lenses are probably not dark enough.
Each year, more than 300 million sunglasses are sold in the US alone. When purchasing sunglasses, people pay more than just a good look. They want to limit exposure to the bright and harmful UV light.
Many countries use standard standards for UV absorption in sunglasses. For example, they use different lens treatments (for example, porized filters or the use of certain shades) to prevent glare on the sunglasses or to increase contrasts. Certain shades also make it easier to see in fog or on cloudy days.
Tinting lenses, also known as photochromic lenses, are a good middle ground for people who don’t want to switch between regular lenses and sun lenses. These light-sensitive lenses automatically darken after 30 seconds in bright, bright light. Once inside, they clear within 5 minutes.
Sunglasses for everyday use transmit 8 to 40% of the light. With photochromic lenses, the amount of light actually transmitted varies from brand to brand. The dark photochromic lenses transmit 12% (outside) to 85% (inside). Weaker brands let through 35 % (outside) to 85 (inside). To find a comfortable spectrum, it is best to try several brands. While these lenses are suitable for everyday use, photochromic lenses are not suitable for sports with a high degree of glare such as skiing , water skiing, sailing, etc.
For comfortable vision on sunny days, glasses should block 75-90% of visible light. Glasses that absorb at least 75% of visible light protect eyes from blue light. It is difficult to focus on blue light, so people often close their eyes.
To test the optical quality, put on the glasses and look at a vertical line or edge. Move your head forward and back and move your eyes along the lens .
If you notice any wobble in the line, there may be an optical defect in the lens and it may be interfering with your vision.
Not all glasses provide the same UV protection. For the best protection, choose lenses that block UVA and UVB rays between 290 and 400 nanometers. UV protection is recommended for adults and children spending time outdoors.
Older sunglasses reduce visible light but offer little protection against glare. Since 1936, polarized lenses have been able to control glare by absorbing light that travels in all directions except 1 – the vertical plane.
Polarization has nothing to do with ultraviolet UV protection, but polarized lenses usually contain chemical elements that block UV.
Polarized filters are added to the lenses through a lamination process. Hard resin and high index lenses are polarized during molding. The polarized films are added to plastic and polycarbonate lenses while still in a liquid state.
An anti-glare coating reflects intense light to reduce glare. It reduces the amount of visible light reaching the eye, but it does not block UV light. Colorful anti-glare, silver, blue, brown-red or orange-gold are primarily for fashion and not for eye protection.
To produce an anti-glare coating, a thin layer of evaporating metal is bonded to the outside of the lens in a vacuum. Metallic anti-reflective coatings, for which chromium is sometimes used, are less durable than high-performance insulating anti-reflective coatings, titanium or quartz. Anti-glare results in dark sun lenses.
- Light gray which transmits 35 to 45% of visible light
- Medium gray which are sometimes used with photocromatic and anti-glare lenses
- Dark gray which transmits 14 to 25% of the visible light
- Light brown or runtan color which transmits 27 to 29% of the visible light
- Dark brown which transmits 18 to 17% of visible light
- Yellow which transmits 68 to 71% of visible light
- Yellow-brown a highly image-sharp filter that blocks blue light
Neutral gray or brown for indoor or computer transmits 60% of visible light
Color and tint
The degree of obscuration of the lenses and/or their color are poor parameters for knowing something about the amount of UV rays that are absorbed. To absorb UV rays, UV-absorbing chemicals are used, which are added to glass, polycarbonate and plastic. These chemicals are usually colorless. Even clear glasses block UV light when treated with these chemicals.
Glasses come in different colors and shades. A weak degree of obscuration of the lenses is good for everyday use. A strong blackout is necessary in very bright light conditions, such as outdoor sports.
Helpful guide when choosing the color of the glass
- Allow true color perception
- Popular neutral color
- Good for general use
- Does not increase contrast
- Good for golfing, cycling or walking
- Allow true color perception
- Popular neutral color
- Good for general use
- Weak contrast in poor lighting conditions
- Reduces nuisance in bright light conditions
- Better in bright sun
- Increases contrast
- Good for sports with strong light conditions, such as skiing, fishing, sailing
- Blocks blue light
- Good in foggy or very cloudy environment
- The world does get a yellow or orange color
- Gives very good contrast
- Good for sports people, pilots, skiers
- Perfect depth perception
- Excellent contrast in low light conditions
- Standard for skiers in foggy conditions
- Good for hunters
- Excellent depth perception in low light conditions
- Contrasts objects against a blue or green background
- Good for skiers or sports people
Not all sunglasses block the same amount of UV rays. Since the color of the glass has nothing to do with the amount of UV rays it blocks, it is difficult to say how much protection a particular color of glass provides. That is why in many cases a sticker is stuck to the glass, stating the amount of UV rays that are filtered.
Regularization around sunglasses
Several regulatory organizations have established standards for protection against UV light. In the United States this is the ANSI standard, in Europe the CEN.
ANSI includes 3 standards for both cosmetic quality, refractive properties (e.g. distortion) and resistance to impact. Sunglass lenses are thus divided into three groups:
- Cosmetic : blocks at least 70% of UV-B and 60% of UV-A
- General use : blocks at least 95% UV-B and minimum 60% UV-A
- Special use : block at least 95% UV6B and 60% UV-A.
If sunglasses in the United States do not meet one of these three groups, the company is obliged to provide the glass with a sticker ‘not suitable for driving’.
According to CEN standards, sunglasses are divided into four groups, depending on their properties to filter UV rays: weak, medium, strong and intense. Glasses belonging to the latter group are not suitable for use while driving.
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