Performance oriented sunglasses, suitable for activities such as skiing, climbing, or mountain biking need to be lightweight, flexible, and durable. More importantly, they should have deluxe optical-quality lenses that offer adequate UV protection.
Sunlight contains a spectrum of Ultraviolet (UV) rays, the invisible part of light. Within the spectrum, UVA and UVB are of greatest concern. UVA rays can penetrate deep into the skin and eyes, and are believed to cause cell structure damage, eye cataracts, and other forms of eye damage. The damaging effects of UVB rays are more immediate. They are responsible for sunburns, accelerating surface skin aging, and are closely linked to the development of skin cancer and cataracts. UVB rays are more intense in the summer months, while UVA rays are relatively constant year-round.
The Canadian Standards Association (CSA) has adopted the voluntary American National Standards Institute (ANSI) standards for UV-protective eyewear. According to these standards, for a lens to be rated 100% UV protective, it must block 99% of UVB radiation. UVA can be no more than half the visible transmission. Another reliable definition of UV protection is known as “UV400.” This term refers to the UVA radiation that extends into the blue-violet part of the visible spectrum. In simpler terms, UV400 blocks a minimum of 99.9% UVB and 99% UVA. It is the UV400 rating that distinguishes high-quality sunglasses from cheaper sunglasses. All MEC lenses are given a UV400 rating. Additionally, MEC glass lenses are tempered in accordance to impact standards. However, MEC still recommends polycarbonate lenses for outdoor activities where there is a chance of impact (skiing, climbing, etc.).
All MEC lenses are rated for light transmission as well as UV protection.
Plastic lenses are less expensive to manufacture than glass. You'll find them in most discount sunglasses. They are heavier, less impact-resistant, and although some have a reasonable level of UV protection, they aren't the best choice for outdoor pursuits.
Polycarbonate lenses are optically superior to regular plastic. They are tough, light, and impact-resistant. Additionally, they can offer excellent optical quality and the material is naturally UV resistant. Polycarbonate is a relatively soft plastic that can be shaped without compromising optical quality. Although polycarbonate lenses are not as scratch-resistant as glass, they are lighter, and much more impact-resistant.
Glass lenses are the gold standard in optical quality, they are also very scratch-resistant. That being said, they tend to be quite heavy which makes them less suited to aggressive activities like skiing, mountain biking, or whitewater kayaking. In addition, despite being hardened or tempered, they can still shatter on sudden impact.
Polarized lenses reduce the distracting glare from light reflected from surfaces like snow, pavement, and water, alleviating eyestrain and fatigue. However, because they are so effective at reducing glare, they may not be suitable for activities that require a high level of light/dark contrast definition, like downhill skiing or mountain biking. Also, polarizing filters can somewhat reduce optical clarity.