Light travels as electromagnetic waves, similar to the waves of the sea, with peaks and valleys. We show the different colors of light by the wavelength of the radiation they emit. (The wavelength is the distance between two adjacent peaks or troughs of that wave). If the light has a wavelength very small, these measurements are very small and are measured in units called nanometers (nm), where a nanometer is a billionth of a meter!
Thinkthe colors of a rainbow, with red on the outside of the curve and blue / violet on the inside. Red has a wavelength of 710Nm all the way, green and 500nm blue / violet is 400nm. So the wavelength decreases as we move from the red part of the visible spectrum through the blue side. Ultra-violet lies beyond the blue / violet band between wavelengths 400nm to 100nm, but the human eye can not usually see light with wavelengths less than 400nm, making ultra-violet lightinvisible to us - as we call it ultraviolet radiation.
Although UV radiation is invisible to humans, many animals and insects, for example, to detect UV light, which are used to help find prey, etc., kestrels by detecting the UV light traces of urine that field voles as they move, so high in the sky, when many birds of prey crossing urine marks on the ground, this is a good place to hunt voles indicates.
Apossible reason why we can not detect UV light is that if the lens in the human eye has evolved to target only a limited number of colors, which helps to give us a clearer picture of what we see, but if you could focus on a wider range of wavelengths could lead to chromatic aberration, a distortion of vision that reduces clarity.
Ultraviolet radiation can be divided into three main bands or groups, depending on wavelength: -
1. UVCradiation - 100 to 290 Nm
UVC rays are absorbed by the all-important ozone layer that surrounds the Earth as part of the outer atmosphere, thus preventing the solar radiation reaches the ground.
2. UVB radiation - 290 to 320nm
UVB rays are the most dangerous, because this is what can damage the eyes and cause sunburn to the skin. UVB is the cause of snow blindness, where the radiation causes a photochemical reaction in the cornea and conjunctiva overlyingAfter a few hours exposure, producing swelling of the cornea (edema) and inflammation of surrounding tissue. The swollen, oedematous cornea becomes cloudy - hence the blurred vision, and also very painful. There is photophobia (dislike of any exposure to light) and spasm of the eyelids. It usually takes a couple of days, and is lit only by the use of drops of local anesthetic, Amethocaine 1%, to reduce pain, and adrenalin drops 0.01% to relieve congestion.
UVBradiation is not glass, so a simple glass lens would prevent reaching the eye. Polycarbonate, a type of plastic used for lenses sometimes glasses and sunglasses, also completely cuts.
Some believe that regular exposure to UVB radiation can, over time, contribute to cataract formation at an earlier age than normal, and can also lead to the development of pterygia, which are growths of tissue that the violation of the sides of the cornea.
UVBradiation varies with time of day, the most intense between 10 hours and fourteen years, when the sun is at its brightest. E 'stronger at high altitudes, and more intense near the equator, due to the nature of the most direct rays of the sun in this region.
3. UVA radiation - 320 to 400nm
Unlike UVB, which varies in intensity with time of day, UVA radiation is more constant with less variation. It is also not blocked by glass, and can continue through the eye to reach.However, the lens of the human eye absorbs most of the UVA radiation, so hardly any UVA can pass to the back of the eye. There is no known evidence that UVA causes harm to the eye, although scientific opinion is still divided and under discussion.
UVA radiation was originally thought that only a small effect on the skin, but recent studies have shown that whilst UVB causes damage to the superficial layers of the skin as sunburn, the UVA rays penetrate deeplayers of the skin, causing further damage down.
Reflected light
UV radiation not only reaches us directly from the sun, but a significant portion is reflected from various surfaces around us, indirectly, to reach our eyes and skin. Fresh snow can reflect more, with up to 80% reflected UV rays. On holiday on the beach, sand can reflect 15% UV light, with concrete buildings and walls etc. A foaming, frothy sea reflects 25%, whereas still water andnormal ground reflects around 10% UV radiation.
Choice of Plain Sunglass
Ideally, you should go for a tint that at least 98% of both UVA and UVB absorption. If you have a "UV400" label, this means that all radiation up to 400nm (thus all UV radiation) is absorbed or blocked by the lens.
Dark gray, gray / green or brown are the three main colors to choose from, and is a personal preference. I myself prefer gray or gray / green, because it seems to adhere tonatural colors, but many people like Brown, because it can improve the contrast and so help to make things appear sharper. Amber tints are used to block the blue light, which again enhances contrast, so as to make the image sharper. Amber tints can therefore be used for skiing, sailing, flying, shooting, etc.
Polycarbonate lenses absorb most UV radiation, and wrap around designs are good for avoiding the light in the eyes ofsides.
Children and UV Light
As UV damage tends to build over many years of exposure, such as going on holiday to warm bright climates or playing outside on a sunny day, children and young adults are particularly at risk, and you must always leave some sort of protective eyewear even if they seem to cope with the light better than us adults (when playing on the coast, for example). She is wearing a hat is not really enough protection,like most of the UV radiation is reflected from the ground (see earlier "reflected light") and in the eyes, especially on a sandy beach. Ensure that a full UV protection sunglasses.
Advice on which shades to choose sunglasses
shades of color are available to enhance vision and improve visual comfort for many activities. Sunglasses are very important because they reduce glare and protect against harmful ultraviolet radiation. L 'Main colors can be divided into neutral gray polarizing, yellow-brown, green, red and photochromic.
1. Neutral Grey
This filters out all wavelengths of light by an amount equal, so the colors appear more natural looking than with reflections of other colors. Shades of gray are good for activities where subtle color differences are important, such as golf, mountaineering and skiing.
2. Polarized shadows
Polarised tints are good for reducingglare from reflected light bouncing off surfaces such as water or wet roads, making them a good choice for fishing, water sports, driving or cycling (on wet surfaces). E 'details can polarized lenses are less important for skiing or golf.
3. Yellow / Orange
Yellow or amber tints help to increase contrast by blocking the blue part of the visible spectrum, resulting in a reduction of the spread of blue light. They increase the differences in profile andthings brighter in low light levels. This makes yellow or amber tints good for shooting, skiing, riding and cycling.
4. Vegetable
Green tints help to explain the background, which makes them an excellent choice for golf, tennis and some forms of shooting, in which the object should be considered in the context of improving.
5. Reds
Red tints enhance objects at the red end of the spectrum, and can be used in skeet shootingwhere the target is orange, in skiing to give contrast to the changes of reflected light, or in motorsport on the road to reduce the reflected glare.
6. Mirror shades
Mirror tints limit glare, increase absorption and reduce infra-red, so the heat build up. Mirror tints are good for winter sports, water sports, cycling and running.
7. Anti-reflective coatings
anti-reflective coating to minimize glare lenses, especially from the rearsurface, and are recommended for racket sports, fishing, shooting and archery.
8. Photochromic tints
In photochromic tints the darkness of the tint changes according to light intensity, usually between about 20% to 80% transmission. Generally, two photochromic colors are available, brown or gray. Photochromic lenses are good for sports played in variable light levels, such as golf or tennis.
The following list provides a summary of the proposed colorsfor sports and other activities: -
Cycling - polarizing, yellow / orange
Golf - green, neutral gray, yellow / orange, brown
Shooting - reddish-brown, orange, yellow to brown, green
Skiing - brown, red / orange, neutral gray
Tennis - green
Fishing - Polarized
Motorsport - polarizing, yellow, red
Water Sports - polarized brown or gray
Running - green, neutral gray
Football, and fast-moving ballsports - amber
I hope this guide is of some use to you, but remember that it is only a guide, so feel free to take "light" (pardon the pun - I could not resist) as the tint color of your choice for your sunglasses is very personal, so if you have a particular color of tint that falls outside these guidelines are preferred - do not worry. As long as it blocks all ultraviolet (UV 400) then the matter is that all. Enjoy your sunglasses!
My Links : Garden Weathervanes Shark Vacuum
No comments:
Post a Comment