How to choose a suitable for your sunglasses in summer

Science according to the optical society of America's web site, summarizes the old beam translation sunglasses buying guide, very informative, you get.
First, people should wear sunglasses in outdoor activities, whether in work, drive, or in sports, walking, running.
Why need sunglasses?
Uv filter
The sun's ultraviolet (UV) radiation can cause human cataracts, pterygium, eyelid skin cancer and electro-optic ophthalmia (also called snow blindness, corneal injury). Wide-brimmed hat can block ultraviolet light of 50% to the eye, so you also need to wear sunglasses.
Filter the blu-ray
Long exposure to uv and blue light frequency, is the old age in age-related macular degeneration (AMD) risk factors of the disease. (old beam added: age-related macular degeneration, europeans prevalence rate 12.3%, Asian 7.4% prevalence, Wan Ling Wong, Lancet Global Health, 2014).
The feeling of comfort
Bright and dazzling sunlight will make eyes uncomfortable, depending on the impact of clarity, people will squint and tears.
Strengthen the dark adaptation
In the bright sunlight for 2-3 hours, people on indoor lighting and adaptability will reduce in the night, lead to drive at night is more dangerous.
How to buy the quality guarantee sunglasses
The basic requirement of sunglasses
Block 99-100% of UVA and UVB rays;
75-90% of visible light;
Depending on the both absorb ultraviolet light, and does not cause distortion and distortion
Don't misled by fake UV filter marks
(lenses 100% UV absorption or UV400 annotations). In order to ensure that the label is true, the best lens UV filtering performance can be detected in the store to buy sunglasses, or buy from formal channels.
Old beam review: at the time of Beijing, cory a little nurse bought fake D&G sunglasses, wearing a walking dizzy and sick. This suggests that the fake lens dioptre is not zero.
Lens color uniform, a region not dimmed
If it is a gradient lens, lens color should be from the top down gradually becomes shallow. Wear sunglasses when driving should be gray (gray, smoke gray, celadon), this does not affect to distinguish the color of the traffic lights.
Make sure the lens distortion does not produce vision
Take sunglasses, unbend arm, through the lens look into the distance square or straight line (such as doors, Windows). Picture frame, slowly moving up and down or so, if there is a distortion, deflection, bending, distortion, suggesting that vision lenses with optical defects, is not qualified.
To ensure that sufficient optical lens can stop
In front of the mirror, try it. If the lens is easy to see through my eyes, that the color of the sunglasses are dark enough. Note: this method is not suitable for color lenses.
The weight of the sunglasses evenly distributed on the nose and ears
Careful adjustment of the radian of frames and nose position, picture frame not pinch the bridge of the nose, nor ears. When wearing, eyelash not exposed picture frame.
Polarized sunglasses
Polarized sunglasses
Can reduce the glare, used for horizontal road and the water, ice and snow. While driving, skiing, water skiing, golf, ride a bike when wearing. Cataract surgery, and sensitivity to the elderly, choose the polarized sunglasses can improve visual comfort. Drive note, polarized glasses, will can't see the car LED display, GPS and mobile phone screen, ATM and pumps of the digital display, etc. Recommendation: yellow, brown, green, can filter blue light.
Polarized sunglasses can not be used in flight. In some sports, such as playing golf, wear polarized sunglasses may cause part of visual information loss, impact performance.
Color sunglasses
Myopic people like the convenience of color sunglasses, the color of the lens with the strength of the light and darker or lighter. Just, when enter indoor or outdoor environment, the lens was not immediately become angry. Car windshields can interfere with the lens color, so in less effective when driving. In a cold environment, the lens color change is slow. Sometimes indoor light is too strong, the lens color is dark, looks very strange. Color change after the lens is not dark, especially in the sand, snow, water sports, such as sunlight intense environment, cannot replace the sunglasses, can't bring enough visual comfort.
Sunglasses mirror surface
One-way mirror oh. The police's uncle like it very much! So each other can't see the eyes of the police and expression, be helpful for self protection.
Mirror reflective coating color variety, this is determined by the thickness of the coating and the structure, and the feeling of the wearer is not colorful, usually brown or gray. Reflective coating will reduce 10-60% through the lens of the light, so very suitable for desert, sea lake, snow snow mountain and high altitudes. Is very popular in the extreme sports.
Sunglasses lens material
Sunglasses price difference, in addition to brand determine prices, and the lens material. Lenses can affect the optical transparency, weight, durability and cost.
Polycarbonate material
Itself can block 100% uv, don't need the lens coating. Impact resistance and transparency is very good, second only to the polyurethane. Cheap, light, no friction resistance, therefore also need sticker.
Polyurethane material
The biggest impact resistance performance, the best optical transparency. Elastic, light, very expensive.
The sunglasses frame materials
The metal frame
Stainless steel, aluminum alloy and super expensive titanium alloy. Very light, but is not suitable for high strength sports. Metal frame sunglasses it's cool, have temperament, but wearing sports would be a little different. On a hot summer, sunglasses in the car, metal frame will become very hot, can not wear right now.
Nylon frame
Is inexpensive, portable and more durable than metal ones. A lot of goggles, sports sunglasses with nylon materials, the radian of the nylon frame generally cannot adjust, unless the picture frame with steel wire core.
Acetate frames
Expensive, light, color variety, low ductility and cannot be used in sports wear.
Visible light transmittance of sunglasses
"Is the color depth, see below, you will find that the same color of the sunglasses with different depth, this performance is called visible light transmittance, 0 to 4 level. Different shades, wear when weather and location are also different: level 0, indoor, cloudy wear; Level 1-2, low brightness sunlight, drive and city life prevent bask in, fashion sunglasses are of this; Most of the sunglasses is level 3, strong light, the sea, mountain climbing wear; Level 4, extremely strong sunlight (snow mountain, desert, mountains and water), can't wear when driving, cycling, vision is too dark.
Helpful hints
Movement when wearing sunglasses is a special design, have prevent slippery nose, nose, the location of the joint stronger still surround type frame, the side of the reflected light is blocked. Infants and young children the color of the sunglasses can choose to brown or gray, gray lenses provide a more natural visual quality, but brown lens can filter harmful short wavelength of the blue, I personally would recommend choose brown.
Reference site information:
http://www.aoa.org/patients-and-public/caring-for-your-vision/uv-protect...? Sso = y
https://en.wikipedia.org/wiki/Mirrored_sunglasses
http://www.framesdirect.com/landing/a/lens-color-guide.html