Polycarbonate lenses: Advantages and disadvantages

When eye safety is a concern, polycarbonate or Trivex lenses usually are the best choice for your glasses, sunglasses, and sports eyewear.

Both polycarbonate and Trivex lenses are thinner and lighter than regular plastic lenses. They also offer 100 percent protection from the sun's harmful UV light and are up to 10 times more impact-resistant than plastic or glass lenses.

This combination of lightweight comfort, UV protection and impact resistance also makes these lenses an excellent choice for children's glasses and safety glasses.

Polycarbonate and Trivex lenses both will provide clearer, more comfortable vision if anti-reflective (AR) coating is applied to the lenses. AR coating eliminates distracting lens reflections that can interfere with vision, particularly when driving at night or in other low-light conditions when glare sources are present.

Polycarbonate lenses

Polycarbonate was developed in the 1970s for aerospace applications and is currently used for the helmet visors of astronauts and for space shuttle windscreens.

Eyeglass lenses made of polycarbonate were introduced in the early 1980s in response to a demand for lightweight, impact-resistant lenses.

Since then, polycarbonate lenses have become the standard for safety glasses, sports goggles and children's eyewear.

Because they are less likely to fracture than regular plastic lenses, polycarbonate lenses also are a good choice for rimless eyewear designs where the lenses are attached to the frame components with drill mountings.

Most other plastic lenses are made from a cast molding process, where a liquid plastic material is baked for long periods in lens forms, solidifying the liquid plastic to create a lens.

But polycarbonate is a thermoplastic that starts as a solid material in the form of small pellets. In a lens manufacturing process called injection molding, 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 lenses

Despite its many advantages, polycarbonate isn't the only lens material suitable for safety applications and children's eyewear.

Trivex lenses were introduced in 2001 by PPG Industries. Like polycarbonate lenses, lenses made of Trivex are thin, lightweight and much more impact-resistant than regular plastic or glass lenses.

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, according to PPG.

Polycarbonate vs. Trivex lenses: A quick comparison

Here is a brief comparison of polycarbonate and Trivex lenses to help you decide which lenses might be best for you:

Thickness

Polycarbonate has a higher index of refraction than Trivex (1.58 vs. 1.53), so polycarbonate lenses are about 10 percent thinner than Trivex lenses.

Weight

Trivex has a lower specific gravity than polycarbonate, making Trivex lenses about 10 percent lighter than polycarbonate lenses.

Optical clarity (central)

Trivex lenses have less internal stress and may produce sharper central vision than polycarbonate lenses.

Optical clarity (peripheral)

Trivex lenses have a higher Abbe value and may produce sharper peripheral vision with less chromatic aberration than polycarbonate lenses.

Impact resistance

Polycarbonate and Trivex lenses have comparable impact resistance.

UV protection

Polycarbonate and Trivex lenses both block 100 percent of the sun's UV rays without the need for special UV-blocking lens coatings.

Availability

Polycarbonate lenses are available in a wider variety of lens designs (e.g., progressive lenses and other multifocals) than Trivex lenses. Photochromic lenses are available in both materials.

Cost

The cost of polycarbonate and Trivex lenses can vary considerably, but many opticians charge more for Trivex lenses than polycarbonate lenses.

Your optician can discuss the pros and cons of polycarbonate and Trivex lenses, and help you decide which lens material is the best choice for your needs and budget.

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Page published on Wednesday, 26 June 2019