All You Need To Know !!!    The aim of this section is to provide a complete reference guide to buying your sunglasses. In addition it will turn you into a witty, attractive person who gets invited to all the best parties - so get reading !
      Which style will suit your face shape?  There's some great advantages to being able to buy sunglasses online - it's quick, convenient and you always have access to the latest styles and offers! However we appreciate that there is a major downside - you can't try the sunglasses on before you buy. To make the decision even easier we have provided you with this straightforward guide to what styles will suit you best, based on your face shape. We hope that this will assist you in your choice of sunglasses! There are 7 basic types of face shape and we have styles which will suit them all . The better matched your sunglasses to your face shape, the more they will flatter your best features and the better you will look!If you are not sure of your face shape, use one of the methods below to determine your classification: 
 •  The simplest way is to use a photograph and draw a line in pen all the way around your face - try not pick out all the detail, it should be just a smooth line. From this you should immediately see the shape of your face. If not look at the pictures below - the one that it most closely matches gives your face shape. 
 •  If you do not have a spare photo, try this. Stand in front of a mirror and look at your reflection (you may want to use a washable pen for the next part as it will be easiest to remove, or you could use a crayon or lipstick!). Draw a line on the glass around your whole face, making sure that you are accurate in following the jaw line. Remember that we are trying to get a general outline of your face so don't make it too detailed. By looking at this outline you will see your face shape, and you can compare it to the pictures below to determine your classification. 
The 7 face shapes            

Oval

Description
            • Balanced proportions
            • Chin is slightly narrower than
            the forehead
            • High cheek bones

Look for ...
            • Frames should be as wide as the broadest part of the face
            • Frames should be the same proportion as the face
            • More frames suit this shape than any other! 
Round

Description
            • Few angles
            • Full face
            • Width and length in same proportions

Look for ...
            • Slightly angular (slight cat eye shape), will narrow and lengthen
            the face
            • Avoid round or very square styles which exaggerate roundness
            • Frames should be wider than they are deep
            • High frames work well.
 Diamond

 Description
            • Small forehead
            • Wide temple area
            • Face narrows to a small chin

Look for ...
            • Frames that are heavy on top will widen the appearance of the
            forehead and jaw
            • Square, oval and rimless frames are great choices.
            • Frames also shaped with a straight top and curved bottoms are
            great for you. 
Triangle (base down)

Description
            • The jaw is the largest part of the face.

Look for ...
            • Frames should add width to the forehead while softening and
            narrowing the appearance of the jaw, chin and cheeks
            • Square, aviators, or semi-rimless styles work well
            • Up swept cat eye styles would work well.  
Heart

Description
            • Wide forehead
            • High cheek bones
            • Face narrows to the chin.

Look for ...
            • Light colours and rimless styles are effective
            • Frames with round tops and square bottoms will work well and
            aviator or butterfly styles
            • Avoid heavy, thick frames.
Oblong

 Description
            • Face shape is longer than it is wide
            • Face is narrow and jaw and cheek bones the same width

Look for ...
            • Frames should have top to bottom depth ie cover a lot of the mid
            section of the face
            • To soften the face, try round, deep or low triangle shapes
            • Decorative or contrasting frame arms can also achieve the
            widening.
 Square

 Description
            • Strong jaw line
            • Broad forehead
            • Wide chin and cheekbones
            • Width and length are same proportions

Look for ...
            • Gently curved narrow styles will minimize square ness and add
            length
            • Frames should be more horizontal that vertical.      

Other considerations 
The size and shape of your nose can also affect which style might accentuate your best features.
      •  If you have a large nose, large oversized frames are recommended for balance. Small frames will accentuate it. .
      •  If you have a long nose, frames with side arms that draw attention to the temples, away from the nose are a good choice. A double bridge helps the nose appear shorter. 
      •  A high bridge in a light colour lengthens a short nose or one that is small in proportion to the rest of the face. 
Still confused? 
If all this information is just too much a good rule of thumb is that the frame of your sunglasses should not be wider than the width of your face and shouldn't sit on your cheeks. It is also said that if you cannot decide which style to choose stick to a rectangular frame as over half of the population suit these!
Shades and Tints
Now you've hopefully chosen your frame you need to choose your tint ! 
Here's a quick guide to what tint you should aim for. 
SmokeDark tint - For daytime (bright and sunny days); decreases sunlight without distorting colors. 
Clear - For low-light or nighttime, untinted for indoor or outdoor use. 
Yellow - For overcast days, increases visibility and depth perception.

Flash Mirror Lens with a partial mirror coating, used for both bright and low light. 
Smoke Mirrored - Smoked lens with a partial mirror coating. 
Revo Mirrored - Revo Mirrored lenses are a multi-layered titanium which provides a brilliant rainbow color. Discovered by aerospace engineers at NASA, these high-tech lenses have 12 layers of titanium 
dioxide and silica applied onto shatterproof polycarbonate. They are also scratch resistant. 
Amber Mirrored - Amber lens with partial mirror coating. Amber lenses enhance contrast, enabling you to make out shapes, objects, and bumps in the snow more clearly because it blocks out the blue, or 
hazy, end of the color spectrum. 
Rose Mirrored - Rose lens with partial mirror coating. Rose lenses enhance contrast, enabling you to make out shapes, objects, and bumps in the snow more clearly because it blocks out the blue, or hazy, end of the color spectrum.

EC Standards 
The CE mark is a mandatory European marking for certain product groups to indicate conformity with the essential health and safety requirements set out in European Directives. In the case of eyewear it indicates conformity with PPE Directive 89/686/EEC and European Standard BS EN 1836:2005. (PPE stands for Personal Protective Equipment)
There are five categories that describe the amount of tint in sunglasses.
Category 0 Clear or very light tint: a clear lens for ordinary glasses and protection 
Category 1 Light tint: usually a yellow or orange lens, often worn by cyclists, and is for protection against grit from the road as well as for enhancing low light in winter 
Category 2 Medium tint: usually a blue lens and will protect against sunlight but not at altitude or where there is reflection from sand and water 
Category 3 Dark tint: the most common available for sunglasses and is good for low mountain altitudes, the seaside and bright days 
Category 4 Very dark tint: essential in high mountains above 3000 metres, regardless of whether there is any snow. These lenses are not recommended for driving as they are too dark

The History of Sunglasses
History says that Nero Claudius Caesar was the one who created the necessary prerequisites for the appearance of sunglasses' prototype. It is believed that the Roman emperor liked to watch gladiator fights through polished gems.However, sunglasses were first used in China in the 12th century or even 
earlier. The "lenses" of those sun glasses represented flat panes of sooty rock crystal, therefore had no correctional power. Such sunglasses were worn only for eye's protection purpose, as from damaging and intolerable sun glare. Also, according to some well-placed sources sunglasses served as a shield from evil spirits. Contemporary writings describe the use of such sun glasses by judges in Chinese courts as a protection, which offered them to keep secret their facial expressions while questioning 
witnesses. James Ayscough, eyeglass designer, started using tinted lenses in spectacles in the middle of 18th century. Only around 1752, Ayscough discovered that white lenses caused irreparable harm to eye's retina, thus he advised the use of green and blue glasses, which had power to correct vision problems. As a consequence, it is considered that Ayscough glasses were the first real sunglasses.
Sam Foster was that man who sold the first pair of sunglasses at the Woolworth on the Atlantic City Boardwalk. But sunglasses' peak of popularity started only in the 1930s. However, polarized sunglasses started to be manufactured only after Edwin H. Land had invented the first modern filters to polarize light. In 1936 Land began to use numerous types of Polaroid material in sunglasses and other optical devices.
Essential information about protecting your eyes (and a great party ice-breaker!)
Factoids
1 Ultraviolet rays are the most dangerous type of radiation. The majority of UV rays are absorbed by the atmosphere, but the quantity filtered is very variable. Those people nearest the equator and at high altitude will be in a thinner atmosphere. The effects of UV radiation are increased if reflected by surfaces such as snow, sand and water . 
2 Water reflects approximately 20% radiation and sand reflects approx 10%. Snow reflects 85% and the intensity of the UV rays increases by about 10% with every 1,000 metres of height gained. It is advisable to have high wrap glasses in the mountains. The higher the relative humidity, the more  dangerous the radiation. 
3 Children, especially very young children have more fragile eyes than adults. UV absorption is total in babies and high under 13 years. 
4 The tint in sunglasses is protecting you against dazzle, which is necessary in itself but dazzle is not harmful to the eyes. Lenses can give total UV protection even when clear. Heavily tinted glasses can do more harm than good as they cause the pupil of the eye to dilate so much, allowing in a lot of UV if the glasses do not have an adequate UV rating. 
5 Lenses that are declared as optically correct are able to transmit a laser beam through them to a centred target with complete accuracy, and not deflect the beam off at an angle. Some lenses cannot do that, which can result in you misjudging your step when walking and making errors when driving. 
What is UV? 
UV (Ultraviolet Radiation) consists of the short, invisible rays from the sun that reach the earth's surface. These rays contain three separate bands: UVA (315-380 nm), UVB (290-315 nm) and UVC (100-290 nm). UVC rays are absorbed by the earth's atmosphere and do not reach the earth's surface and therefore do not relate to sunglass performance. UVB rays are 
the " sunburn " rays. Exposure to UVB rays can potentially produce harmful effects to your eyes and may be associated with cataracts and retinal damage. UVA rays are mostly absorbed within the lens of the human eye, debate over the potential effects of UVA exposure continues within the industry. Sunglass standards place limits on UVA and UVB exposure . UV radiation is strongest at high altitudes, low latitudes and in open or reflective environments (sand, snow or water) 
Are the designations ‘CR' and ‘Hard Resin' essentially the same thing ?                      Generally speaking yes. Both CR-39™ (A registered trademark mark of PPG, which stands for Columbia Research's 39th version of the formula) and Hard Resin (the generic term for standard plastic lenses) are made of a clear, water like liquid (diethleneglycol - allycarbonate) that are part of the thermosetting family of resins. In order to turn into lenses, the resin must be poured into a glass mould and then cured or polymerised in an oven and the resin hardens. Many companies have their own formulations and processes to make Hard Resin lenses. 
What is the difference between "Bent Sheet" and "Injected" Polarized Polycarbonate? 
Bent Sheet (thermoformed) polarized polycarbonate lenses are made by placing polarized film between two thin, flat sheets of polycarbonate material. A lens is formed by cutting out a particular size from the sheet and then heating the lens on a bending tool to achieve the required base curve (thermoforming). Injected polarized polycarbonate lenses are made essentially the same as standard polycarbonate lenses (injection moulding) with the introduction of the polarizing film in the lens mould, instead of lamination. The result is the injected lens provides superior Class 1 optical performance with the film as part of the finished lens.                                                                                                               What is TR90 ?
TR-90 is a superior compound which has no risk of toxicity or allergy and is FDA and BGA approved. It is extremely light weight and designed to flex making it resistant to stress cracking and material fatigue. It is free of plasticizers and extremely stable to UVA exposure in all types of temperature and humidity conditions. Strong resistance to chemical products such as solvents, alcohol, cosmetics and organic acids gives TR-90 maximum durability in outdoor environments.
What is an optically-decentered lens ?
Optically-correct decentred lenses provide superior optical clarity.They achieve this by undergoing a process where the thickness of a deeper base curve lens is horizontally tapered from the  bridge area and becomes thinner at the outer edge of the lens near the hinge. This process eliminates prismatic distortion by shifting the optical sweet spot of each lens from the mid-point of the lens to directly in front of the eye.

To what standards are sunglass lenses measured?                                                          Depending on where they are sold, sunglass lenses must meet the requirements of the standards listed below:                                                                                                                                                 - European Norms - EN 1836-1997 
- American Standards - ANSI Z80.3 - 2001 
- Australian Standards - AS 1067.1 - 1990 (from October 2004: AS/NZS 1067 - 2003)                For Driving and Road Use:                                                                                                       Filters suitable for road use and driving shall be in accordance with specific requirements:                      - Spectral Transmittance European, American, Australian/New Zealand standards must be > 8% 
- For EN and ANSI the spectral transmittance between 500 nm to 650 nm must be > 0,2 x tv. 
- For AS/NZS the spectral transmittance between 450 nm to 650 nm must be > 0,2 x tv.    Recognition of Signal Lights: 
EN 1836 - 1997 ANSI Z80.3 - 2001 AS/NZS 1067 – 2003 Relative visual attentuation quotient Q Traffic Signal Transmittance Relative visual attenuation quotient Q > 0,80 RED signal light                    > 8% RED signal > 0,80 RED signal light > 0,80 YELLOW signal light                                               > 6% YELLOW signal > 0,80 YELLOW signal light > 0,60 GREEN signal light                                 > 6% GREEN signal > 0,60 GREEN signal light > 0,40 BLUE signal light Fulfill the color limit region > 0,70 BLUE signal light                                                                                                                     For Luminous Transmission: 
Ratio of visible light transmitted by the filter between 380 nm to 780 nm Different measuring methods are used by different Standards EN1836 1997 and AS/NZS 1067 2003 ANSI Z80.3 2001 LUMINOUS TRANSMITTANCE tv FILTER CATEGORY LUMINOUS TRANSMITTANCE 
tv Primary function and shade 
80 - 100% 0 > 40% Cosmetic lens or shield, light                                                                             43 - 80% 1 8 - 40% General purpose lens or shield, medium to dark                                                 18 - 43% 2 3-8% Special* purpose lens or shield, very dark                                                                8 - 18%  3 3% Special* purpose lens or shield, strongly color                                                             3 - 8%   4   * Does not meet the requirements of transmittance properties related to traffic              Now don't tell me that wasn't a fascinating read - enjoy !