Glass used to the main material to make lenses. Not anymore, thanks to plastic. Yes, for a simple term we called it plastics but there are many names for these sorts of plastics. Let’s name a few which you might come across, High-Index, Polycarbonate, CR-39, MR-7, NK-55, Trivix, ok just to name a few and not list everything. You must be wondering why so many different types? It all due to the way they are being manufactured, the process steps and the desired function of the lenses.
High Index lens is a much lighter and thinner lenses. The best part is that it allows high prescriptions in Sphere and Cylinder section, typically from -4 to -8. Typically, the stronger your prescription the thicker the edges of the lens. But you do not want to wear spectacle with thick lenses as it spoils your appearances. Therefore, if you have a high prescription, best is to go with High Index lenses and they are more expensive, unfortunately.
Polycarbonate differs from high index. This is a much more common lens partly due to its price comparing to high index. Polycarbonate lenses are hardy, meaning it is strong and impact resistant. If you are into safety, then this lens could be the one for you. Most sports eyewear’s use Polycarbonate as they are thinner and lighter than conventional plastics. Highly recommended for kids eyewear.
Polycarbonate is a thermoplastic that starts as a solid material in the form of small pellets. In a lens manufacturing process called injection moulding, the pellets are heated until they melt. The liquid polycarbonate is then rapidly injected into lens moulds, compressed under high pressure and cooled to form a finished lens product in a matter of minutes.
Trivex is similar to Polycarbonate in attributes. They are both thin, light weight, impact resistant. The difference would be the way Trivex is being produced. Trivex lenses, however, are composed of a urethane-based monomer and are made from a cast moulding process similar to how regular plastic lenses are made. This gives Trivex lenses the advantage of crisper optics than injection-moulded polycarbonate lenses.
CR-39 lens is very similar to Polycarbonate but with slight variance. Its optics are better than polycarbonate as it is nearly as good as glass. It is also less lightly to break, and it retains some hardiness from polycarbonate lens. Let’s see a simple matrix to help you to decide which type of lens you should buy.
|Optics||Best quality||Poor||Close to glass|
|Hardness||Poor||Very strong||Close to very strong|
Ok I’m stopping here for now. Happy reading and come back again for more.