Sunglasses Guide: UV400, Polarisation, Lens Categories and Colours

Sunglasses are often treated as a fashion accessory, but they are also a piece of health equipment. Ultraviolet (UV) radiation from the sun can damage the eyelids, the surface of the eye and the structures inside it, and the effects add up over a lifetime. Bright light and glare also reduce comfort and can make driving, cycling or skiing more dangerous. The good news is that effective protection does not have to be expensive, as long as you know what to look for.

This guide explains how UV affects the eyes, what labels such as UV400 and CE mean, how the international filter categories 0 to 4 work, which lens colours suit which activities, the pros and cons of polarised lenses, how to protect children's eyes and the options for people who wear prescription glasses. For a shorter checklist, see our article on how to choose sunglasses that truly protect.

Why the eyes need sun protection

The sun emits UVB (280 to 315 nm) and UVA (315 to 400 nm) radiation that reaches the earth's surface. The cornea and lens of the eye absorb most of it, which protects the retina but exposes these front structures to cumulative damage. According to the WHO and AAO, long-term UV exposure is linked to:

• Cataract: clouding of the eye's natural lens; UV exposure is one of several risk factors. See our page on cataract.
• Pterygium and pinguecula: growths on the white of the eye, common in people who spend a lot of time outdoors in sunny, windy or dusty climates. See pterygium and pinguecula.
• Skin cancers of the eyelids: the eyelids are a common site for basal cell carcinoma.
• Photokeratitis: a painful, temporary sunburn of the cornea after intense exposure, for example on snow or water, also known as snow blindness. Our article on snow blindness and UV damage explains it in detail.

UV levels are highest around midday, in summer, at high altitude and near the equator. Snow can reflect up to around 80 percent of UV, and water and sand also reflect a significant amount, so exposure can be high even when it does not feel hot. Clouds do not block all UV, so protection matters on hazy days too.

UV400 and protection labels

UV400 means the lenses block light with wavelengths up to 400 nanometres, which covers all UVA and UVB. Labels such as 100% UV protection or 99-100% UVA/UVB mean essentially the same thing. In the European Union, sunglasses must meet the standard EN ISO 12312-1 and carry a CE mark; in the UK the UKCA mark is used, while in the US and Australia there are national standards with similar requirements.

Price is not a reliable guide to UV protection. Inexpensive sunglasses from reputable retailers that meet these standards can protect as well as designer brands. The risk lies with unlabelled novelty glasses or counterfeits. An optician can test your sunglasses with a UV meter if you are unsure.

Filter categories 0 to 4

The international standard groups sun lenses into five categories according to how much visible light they let through (luminous transmittance). The category number is usually printed on the inside of the temple arm.

All categories, including category 0 lenses sold as sunglasses, should block UV. The category only describes darkness and comfort in bright light. For driving at dusk or night, no tinted lenses should be worn; the standard restricts night driving to lenses that transmit more than about 75 percent of light, and many experts advise clear lenses only. Our article on night driving vision covers glare and halos after dark.

Lens colours: function and style

Lens colour changes how you perceive contrast and colours, but it does not affect UV protection. Common choices include:

• Grey: reduces brightness evenly with the most natural colour perception. A good all-round choice, including for driving.
• Brown or amber: enhances contrast and depth perception, especially in variable light, and makes greens and blues appear warmer. Popular for driving, golf and fishing.
• Green: a classic option that balances contrast and natural colour perception, reducing some glare.
• Yellow or orange: increases contrast in fog, haze and flat light, for example in skiing in cloudy conditions. Usually lighter categories; they distort colours and are not ideal for bright sun.
• Rose or red: enhances contrast in some outdoor sports and low light; can be pleasant for screen work for some people.
• Blue, purple and mirror finishes: mainly aesthetic, though mirror coatings add some extra light reduction in very bright conditions.

Polarised lenses: pros and cons

When sunlight reflects off flat surfaces such as water, wet roads, car bonnets or snow, the reflected light becomes partly polarised horizontally and creates intense glare. Polarised lenses contain a filter that blocks this horizontally polarised light. The result is less glare, more comfortable vision and better visibility into water.

Advantages

• Greatly reduced glare from water, roads and snow.
• Improved comfort and reduced squinting on bright days.
• Better visibility beneath the water surface for anglers and boaters.
• More relaxed driving in bright, reflective conditions for many people.

Disadvantages

• LCD screens, including phones, some car dashboards, GPS units and cash machines, may look dark, patchy or rainbow-coloured at certain angles.
• Polarisation can mask the glare that signals ice on roads or slopes, making hazards harder to spot.
• Pilots are generally advised not to use polarised lenses, because they can interfere with instrument displays and seeing glints from other aircraft.
• They usually cost more than non-polarised lenses.

Polarisation does not by itself mean UV protection, although most quality polarised sunglasses also block UV. Check both labels.

Frame shape and fit

A meaningful share of UV can reach the eye from the sides, top and from reflections off the back of the lens. Larger lenses and wraparound or close-fitting frames reduce side exposure. A back-surface anti-reflective coating reduces reflections from behind. Combine sunglasses with a wide-brimmed hat, which the WHO and many health organisations estimate can substantially cut the UV reaching the eyes. If you are choosing between frames, our frame guide covers sizes and fit.

Sunglasses for children

Children spend more time outdoors than most adults, and the lens of a young child's eye transmits more UV to the retina than an adult's lens. Much of a person's lifetime UV exposure is thought to occur before adulthood. Protecting children's eyes is therefore important.

• Choose sunglasses labelled UV400 or 100% UV protection that meet recognised standards, not toy sunglasses.
• Pick impact-resistant polycarbonate or Trivex lenses and flexible, unbreakable frames, with a strap for toddlers.
• Category 2 or 3 lenses are usually suitable for sunny days; category 4 is for special situations only.
• Combine sunglasses with a wide-brimmed hat and shade, especially around midday.
• Babies under six months should mainly be kept out of direct sunlight.

Outdoor play remains very beneficial: daylight is linked to a lower risk of developing myopia. The aim is to protect children's eyes outdoors, not to keep them inside. Read more in our page on glasses for children.

Prescription sunglasses and other options for glasses wearers

If you wear glasses, you have several ways to protect your eyes in the sun:

• Prescription sunglasses: tinted or polarised lenses made to your prescription, available in single vision and progressive designs. They give the best optics and wide coverage. Strongly curved wraparound frames may be limited with higher prescriptions.
• Photochromic lenses: clear indoors and darken in UV light. Convenient, but most darken little behind a car windscreen and are rarely as dark as category 3 sunglasses. See our page on lens coatings and treatments.
• Clip-on or magnetic sun lenses: attach to your regular frames; affordable and practical, but quality varies.
• Fit-over sunglasses: large sunglasses worn over your glasses. Useful after eye surgery or for occasional use.
• Contact lenses with sunglasses: standard sunglasses can be worn over contact lenses. Some contact lenses contain UV blockers, but they do not cover the whole eye and do not replace sunglasses.

Special situations

After eye surgery or with certain conditions

After cataract surgery, laser refractive surgery or in conditions such as uveitis, some people are more sensitive to light. Certain medications, including some antibiotics and other drugs, can increase sensitivity to sunlight. Your eye doctor may recommend specific protection.

Snow, mountains and water sports

On snow and at altitude, use category 3 or 4 wraparound sunglasses or goggles with full UV protection. For water sports, polarised lenses and a floating strap are practical. Never look directly at the sun, including during a solar eclipse, without certified eclipse viewers; ordinary sunglasses are not safe for this purpose.

When to see a doctor

See an eye care professional if you develop a growth on the white of the eye, a persistent lesion or change on the eyelid skin, increasing glare or blurred vision, or if you are very sensitive to light. Regular eye examinations help detect sun-related changes early.