The Difference between Polycarbonate and Plastic (CR 39) for Prescription Eyewear Lenses
There are a variety of lens materials to choose from when selecting prescription safety glasses. If the eyewear is single vision, progressive no-line bifocal, line bifocal safety glasses, or even fashion safety glasses the lens material is an important element of the eyewear you choose. Glass was the initial lens material for eyewear and therefore has been around a long time. However, glass lens were heavy and strong prescriptions resulted in thick lenses. Then came along plastic lens material known as CR-39, which was introduced in the late 1940’s. The plastic lens material was lighter weight than glass, which was predominately used at that time. Up until the early 1980’s CR-39 was the best choice for light weight glasses. In the early 1980’s, however, polycarbonate lens material was introduced for use in eyewear. It quickly became the lens material of chose due to its lightweight, impact resistance, durability, and shatter resistance properties.
Currently, polycarbonate lens material is the standard for prescription safety glasses, sports glasses, outdoor eyewear, as well as fashion eyewear. Its popularity is due to its light weight, impact resistant, and virtually shatter resistant qualities. Polycarbonate lens are up to ten times more impact and shatter resistant than plastic CR-39 lens material. For the same prescription polycarbonate lens will be significantly lighter than the CR-39 yet more impact resistant. The plastic CR-39 lens is slightly less expensive to manufacture but is not as durable compared to polycarbonate lens material.
Polycarbonate lens material is also very adaptable to adding features to the lenses such as transitions, which are lens that darken when exposed to UV sunlight when the wearer is outdoors. Anti-reflective coating can be easily applied to this lens material as well. The anti-reflective coating reduces glares on both the front and back of the lens surface. This improves your vision making you safer and eliminating eye strain. Sunglasses use polycarbonate lens as well because they are very accommodating for polarized lens. Further, polycarbonate lenses are the superior choice for rimless, semi-rimless, or drill mounted frames.
Strong prescription lens can be a problem with plastic CR-39 material due to the thickness required to produce the higher diopter prescription. Polycarbonate lens material on the other hand is comparatively thinner for strong prescriptions which provides the wearer with a lighter weight pair of glasses.
Polycarbonate lens are soft and flexible which makes them impact and shatter resistant. However, due to the properties being less dense than CR-39 the polycarbonate lens is slightly easier to scratch. Therefore, adding a scratch resistant coating to the polycarbonate lens is highly recommended in an industrial application, sporting endeavors, and outdoor activities. In fact, even fashion glasses benefit from adding a scratch resistant coating to protect your eyewear during everyday use. Polycarbonate lens material are extremely receptive to any kind of coating materials including scratch resistant coatings.
To better understand the differences between polycarbonate and plastic CR-39 lens material it is always a good idea to discuss your choices with a knowledgeable optician. You can get all your questions answered when you consult with an experienced knowledgeable optician. An optician can provide insight you may not have thought of, and this will help you obtain the best pair of glasses with the most suitable lens material for your needs.