Understanding Lenses

Lens Material

The material used in your sunglass lenses will affect their clarity, weight, durability and cost.

  • Glass—PROS: Superior optical clarity; superior scratch-resistance. CONS: Heavier than others; expensive; glass will "spider" when impacted (but not chip or shatter).

  • NXT polyurethane—PROS: Superior impact-resistance; excellent optical clarity; flexible and lightweight. CONS: Expensive.

  • Polycarbonate—PROS: Excellent impact-resistance; very good optical clarity; affordable; lightweight and low bulk. CONS: Less scratch-resistance; slightly less optical-clarity than glass or NXT.

  • Acrylic—PROS: Inexpensive alternative to polycarbonate, best suited for casual or occasional-use sunglasses. CONS: Less durable and optically clear than polycarbonate or glass; some image distortion.

Lens Color (Tint)

All sunglass lenses are tinted to cut down on overall brightness and enhance terrain definition. But your choice of tint colors affect your vision by influencing 1) how much visible light reaches your eyes, 2) how well you see other colors, and 3) how well you see contrasts.

  • Brown/gray/green—Brown, gray and green lenses are color-neutral, which means they cut down on overall brightness without distorting colors. These darker shades are intended primarily to cut through the glare and reduce eyestrain in moderate-to-bright conditions.

  • Yellow/gold/amber—Yellow, gold and amber lenses provide less overall brightness protection, but excel in moderate-to-low level light conditions. They provide excellent depth perception, which makes them perfect for skiing, snowboarding and other snow sports. They also enhance contrasts in tricky, flat-light conditions.

  • Rose/vermilion—Rose- and vermilion-colored glasses really do make the world seem brighter. They provide excellent low-light visibility and enhance contrast (perfect for skiing and snowboarding in cloudy conditions). They also enhance the visibility of objects against blue and green backgrounds, which makes them ideal for driving or exploring in forested areas.

  • Mirrored or flash coating—This refers to a reflective film applied to the outside surfaces of some sunglass lenses. They reduce glare by reflecting much of the light that hits the lens surface. Mirrored coatings make objects appear darker than they are, so lighter tints are often used to compensate for this.

Lens Coatings

The more expensive the sunglasses, the more likely it has several layers of coatings. These can include a hydrophobic coating to repel water, an anti-scratch coating to improve durability and an anti-fog coating for humid conditions or high-energy activities.

Lens Constructions

Two methods are commonly used. Lenses made via the injection process offer the best in optical clarity, but are more expensive. The bent-sheet process is used to make both performance and inexpensive glasses. High-end styles use a longer process to offer similar optical clarity as injected models, while lower-cost styles used a simplified process that yields a bit less clarity.

Interchangeable Lenses

Some styles come with interchangeable (removable) lenses of different colors. These multi-lens systems allow you to tailor your eye protection to your activities and current conditions. Consider this option if you need reliable performance in a wide variety of situations.

Polarized Lenses

Polarization is a great feature if you enjoy water sports or are especially sensitive to glare. When light reflects off of flat surfaces, such as a lake, the light waves align in horizontal patterns, creating intense glare. The filters in polarized lenses block these horizontal light waves, substantially reducing blinding glare and its resulting eyestrain.

In some instances, polarized filters react with the tints in windshields, creating blindspots and diminishing the visibility of LCD readouts. If this occurs, you should consider mirrored lenses as a glare-reducing alternative for driving.

The method used to polarize lenses affects both the optical-quality and cost of the sunglasses.

  • Inexpensive casual styles have the polarizing filter applied as an external film coating.

  • More durable and expensive sport styles sandwich the polarizing filter between layers of the lens.

  • The newest high-end technology combines the polarizing filter with the lens material while the latter is in a liquid form. This allows the filter and lens to bond without the use of adhesives and sustains an exceptionally high optical quality.

1 comment:

MITCH said...

Why do you not mention blue tinted lens. Are they truely harmful to the eyes. Is there scientific evidence to this.

Thanks
I want my regular eye glasses tinted blue.