When you are spending lots of time outdoors, looking after your eyes is crucial. If you don’t have technical sunglasses yet, you should consider buying them.
Technical sunglasses for expedition or sports use are among the most under-rated items in an outdoor equipment. Everybody has to protect themselves from the sun and, while skin usually gets the most attention, eye care is equally, if not more, important.
Sunglasses for active use need to have frames shaped to allow ventilation in tandem with side protection: light reflected off bright surfaces such as water, snow, or even shiny rock can affect the eyes both from the sides and the front.
Most lenses for active use are made of polycarbonate or Trivex. These materials are lightweight, thin, ten times more impact-resistant than traditional lenses and offer complete protection for eyes from the sun. What is more, they are virtually shatterproof, with treatments including oleophobic (resistant to oil contaminants such as fingerprints), hydrophobic, and anti-fog.
Polycarbonate lenses are extremely strong, made from injection-molded thermoplastic and the material of choice until Trivex was created in 2001. In comparison to polycarbonate, Trivex is a molded, urethane-based monomer which uses a different construction process; it is thinner, lighter, and with glass-like clarity.
When it comes to performance, lenses are classified into categories from 0 to 4:
- Category 0: stops up to 20% visible light
- Category 1: stops 20-57%; for use in weak sunlight (usually yellow/orange lenses)
- Category 2: stops 57-82%; for use in moderate sunlight
- Category 3: stops 82-92%; for use in strong sunlight
- Category 4: stops 92-97%; for use in extremely strong light (not suitable for driving)
All photographers who use filters know that light rays spread in all directions when they hit a flat surface. This can be dealt with in sunglasses by incorporating a polarized filter into each lens, which results in reduced glare.
Beside category ratings, some brands refer to base curve, which is the width of lens curvature. Wider lenses offer the widest field of vision and eliminate sun from the sides, so 1-base curve is almost flat, while 10-base curve has the maximum wraparound; 8-base curve is standard for sports glasses.
Optical quality it shown mainly in lens clarity: the best provide crystal-clear vision, some are less crisp, with vision being smoky, or almost smudged.
Prescription sports sunglasses are becoming more widely available, as clip-in inserts or glazed lenses.
When buying new technical sunglasses, pay attention to the following:
- Lenses: Photochromic lenses change category by becoming darker or lighter as light conditions vary. Orange lenses offer better vision in low or flat light, absorbing less light and creating a brightening effect. Some are treated to ensure scratch, impact and/or fog resistance.
- Fit: A close frame fit provides more protection against light but less airflow. Anti-fog treatments and mechanical venting help prevent (or reduce) lens fogging during active use.
- Comfort: Make sure that your sunglasses fit your face shape. Pay attention to grip of nosebridge and arms, flex and adjustability of frames, and how the lenses sit on your cheeks. Chunky or bowed arms aren’t appropriate for use under helmets.
- Cleaning: When you clean lenses, first blow off debris, then use an optical cloth or wash in warm, soapy water, and rinse. Don’t wipe with paper products and never use chemical glass cleaners.
- Rays: Sunlight consists of electromagnetic rays in three wavebands: visible light, infrared (IR) and ultraviolet (UV). Radiation can be direct, diffused by the atmosphere or reflected by clouds, snow and sea.