Sunglasses Facts

The aim of this article 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 !

There is some great advantages to being able to buy sunglasses online - it is quick, convenient and you always have access to the latest styles and offers! However we appreciate that there is a major downside - you cannot 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!

The 7 face shapes

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.

Shades and Tints

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 eyes 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 eyes 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.

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.

UV (Ultraviolet Radiation) consists of the short, invisible rays from the sun that reach the earths 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 earths atmosphere and do not reach the earths 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).

Generally speaking yes. Both CR-39™ (A registered trademark mark of PPG, which stands for Columbia Researchs 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.

Polycarbonate is a tough, dimensionally stable, thermoplastic, while CR-39 ™ / Hard Resin is a thermoset polymer . Polycarbonate is processed by injection moulding. Polycarbonate pellets are heated, injected into stainless steel moulds under pressure and compressed to form a lens. All polycarbonate lenses must be scratch coated, as the uncoated material is susceptible to abrasion. Polycarbonate is lighter in weight and more impact resistant than Hard Resin. Hard Resin tends to be easier to edge and can be tinted (dyed) to a wider variety of lens colours.

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.

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.