One of the things I get asked about a lot is whether to order glass vs plastic prescription sunglasses lenses. Today you can purchase a lot of sunglasses with glass lenses, so it seems natural that when ordering your prescription sunglasses lenses you would ask for glass lenses. But there are some problems to consider when ordering your prescription sunglasses lenses. Let's start with a discussion about the different prescription sunglasses lenses.
Today most high quality (high priced) non-prescription sunglasses use glass lenses. The glass lenses in these sunglasses are very thin for an important reason - to keep them light! Typically most of these lenses are manufactured in one of three different countries: China, Japan or Germany. These are precision ground lenses specially tempered for breaking and shattering to protect your eyes. There are a number of advantages to glass prescription sunglasses lenses:
- Glass lenses will not expand nor contract with hot and cold temperature changes thus retaining their shape;
- Glass lenses are scratch resistant naturally, while plastic lenses must be coated with an anti-scratch coating;
- Glass lenses have the highest optical clarity, which is the primary reason high quality sunglasses use glass lenses;
- Glass will absorb heat and cold better keeping your eyes cooler.
All good reasons to want to have glass prescription sunglasses lenses, right? But there are a number of disadvantages to prescription sunglasses lenses:
- Glass lenses are not as durable as plastic lenses and will break/shatter more easily than plastic;
- Prescription glass lenses are much heavier than plastic lenses, making them more uncomfortable to wear;
- Prescription glass lenses are significantly more expensive than plastic lenses;
- Prescription glass lenses can be significantly thicker than plastic lenses (depending upon the prescription) making them more difficult to fit into some frames.
The reality is that while glass prescription lenses are still being ground here in the United States most optical supply companies no longer grind glass lenses as the demand for glass lenses is so small today versus plastic lenses.
Today most plastic lenses are made from CR-39 plastic. The abbreviation stands for "Columbia Resin #39", which was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940. There are a number of advantages to plastic CR-39 lenses:
- They are slightly better at blocking uv rays because they are more dense than glass lenses;
- Plastic CR-39 lenses are great for sports glasses and sports sunglasses because they are less likely to shatter than glass and can be made extremely strong;
- Plastic lenses are cheaper than glass lenses.
But prescription plastic lenses have their down side as well:
- Prescription plastic lenses will expand and contract with temperature changes, and can even become disfigured in extreme heat;
- To keep plastic lenses from scratching requires that they have coatings applied to the lenses which can wear or peel off over time.
Glass vs Plastic Prescription Sunglasses Lenses
So, which are better - Glass vs Plastic Prescription Sunglasses Lenses? As we can see there are advantages and disadvantages to each choice, but in the end the practical (and perhaps best) choice are the CR-39 plastic prescription sunglasses lenses.
What do you think?
Keep your eyes cool and protected today my friend!