SUNGLASSES - A GLOSSARY OF TERMS

Absorption Factor
This is a measure of the amount of light that is absorbed by a tinted lens.

Acrylic
A plastic material that is very lightweight and often used to make frames for sunglasses.

All-Weather Photochromatic Lenses
These are very good for all weathers as they change to suit the lighting conditions. In overcast days they are light amber and in sunnier conditions they turn darker brown so as to help improve contrast and sharpness whatever the light. This makes them superb for any outdoor activity. It is important to remember that photochromic lenses often need to be worn for a short period of time before they are able to reach their full capacity to change colour.

Anti-Reflective Coating
This is a coating on the back of the lens which stops any sunlight, which comes in from the side of the sunglasses, from being reflected back into the eyes.

Arm
This is the side part of the sunglasses that hold them in place by resting on the ears and the side of the head.

Bridge
The bridge is the area between the two lenses on a pair of sunglasses which rests on the nose. With prescription sunglasses it is important that the bridge size is accurately measured or your vision may be affected.

Brown Lens
These are excellent general purpose lenses. They help to improve contrast by filtering out the blue light and also reduce glare. They are ideal for driving and for sports where high glare is a problem, such as skiing, fishing and boating.

Constant Density
This is where the tint of the lens is uniform, or constant, throughout which means that they are fixed in the amount of light that they absorb. Most sunglasses are of constant density.

CR39
This is widely considered to be the best plastic for making lenses as it has the highest optical rating and offers the best scratch resistance in comparison to other plastic lenses.

Frames
The frame is the body of the sunglasses which holds the lenses in place and allows them to be worn on the head. They can be made of different materials such as metal alloy, acetate, acrylic, graphite, nylon, plastic, polycarbonate, stainless steel, titanium and urethane.

General-Purpose Lens
These are basic lenses which are good for everyday use.

Glare
This is very bright light which is too much for the eyes to handle comfortably and can damage them if it there is prolonged exposure to it. It can come directly from a light-source, most typically the sun, or it can be reflected off surfaces, for example water and snow.

Goggles
Goggles are protective glasses which are set in a flexible frame which fits snugly against the face providing all-round protection. They can come with clear or tinted lenses depending upon the requirements. They are commonly used in sports where the eyes require extra protection from things other than just sunlight, most commonly skiing and water activities.

GPL
This is the abbreviation for Glass Polarized Lenses.

Graphite
This is a combination of carbon and fibreglass. Graphite frames are very strong but also extremely lightweight.

Green Lens
These are excellent all-round lenses which give good contrast in overcast conditions whilst reducing eyestrain in bright conditions. They filter out some of the blue light which helps reduce glare.

Grey Lens
Grey lenses allow colours to pass through quite evenly and without the distortion of other lens colours. This makes them very good for sporting activities, particularly golf, outdoor work and driving.

Hardcoating
This is where scratch-resistant coatings are put on the surface of the lens. They help resist, but do not prevent, scratches on the lenses. They are most commonly used on plastic lenses.

HEV Radiation
This is visible light which is just beyond ultraviolet, or UV, radiation on the light spectrum. It has been linked to severe eye damage.

Hinges
The hinge is where the arm of the sunglasses joins the frame. Hinges can come with a standard screw fitting, with spring joints. In some sunglasses the hinge is fixed as the frame is joined directly onto the arms.

Impact-Resistance
This is the ability of a lens to withstand an impact without cracking or breaking.

Interchangeable Lenses
Some sunglasses provide the facility to change the lenses in order to allow for differing circumstances, environments and light conditions.

Iridium
This is a mirrored coating used on lenses.

Lens
This is the part of the sunglasses which cover the eyes and filter the light to offer improved contrast, perception, comfort and protection. They can be made from glass or other transparent materials, such as plastic.

Light Spectrum
This is how the distribution of energy given off by a light source, most typically the sun, is arranged in order of different wavelengths. Part of the light spectrum can be seen in the form of rainbows.

Metal Alloy Frames
These frames are usually base metal alloys which are then plated to give them an attractive finish.

Mirrored Coating
This is a very thin coating of a metallic material, such as iridium, over a lens which creates a mirror effect.

Nylon
Frames made from nylon are lightweight, flexible and very strong. Nylon frames are very durable.

Photochromic
This is where a material, such as a lens, is able to change colour depending upon the brightness of the light that they are exposed to. Photochromic lenses darken as the light becomes brighter.

Pink Lens
Pink lenses allow very good perception in low light conditions whilst providing a degree of comfortable vision in bright light. They are very good for sporting activities where accurate focus on objects against a dark background is needed, such as archery or shooting.

Polarized Lenses
These lenses have a special filter that reduces glare by only allowing one plane of light waves through them. They are created when a horizontal sheet of material is laminated between two sheets of glass or plastic, or is laminated onto the back of the lens. They eliminate reflective glare which makes them perfect for skiing or water activities.

Polycarbonate
This is a very strong plastic often used in sunglasses frames.

Rim
The rim is the part of the frame that encircles the lens holding it in place. Sunglasses are available as full rim, semi, or half, rim and rimless varieties.

Scratch-Resistant Coating
This puts a durable layer on the surface of the lens which helps resist, but not prevent, scratching.

Side Pieces
The arms of the sunglasses

Titanium
This is a very strong, but lightweight, metal alloy which is sometimes used in sunglasses frames.

Transmission Factor
This is the measurement of the amount of light that passes through the lens.

UVA Rays
These rays can cause damage to the skin. Although there is debate over whether they can cause damage to the eye it is sensible to protect against them by wearing sunglasses.

UVB Rays
These are the rays which have the greatest potential to cause damage to the skin and the eyes. They are known to cause keratitis, an inflammation of the cornea, and have been linked to the development of cataracts. It is always recommended to wear sunglasses that offer protection against UVB rays.

Yellow Lenses
Yellow lenses provide excellent depth perception and contrast in low light conditions. They are ideal for shooting, skiing and sports which require fast reactions.