UV, snow blindness, and why a dark lens is not the same as a safe one

Why snow doubles the exposure

Fresh snow is one of the most reflective natural surfaces there is. A large proportion of the ultraviolet light that reaches it bounces back up, which means that on a snowfield you are being illuminated from above by the sky and from below by the ground at the same time.

Altitude compounds it. There is less atmosphere above a mountain to absorb UV, so the light arriving at 9,000 feet is more intense than the same sunlight at sea level. Put the two together and a bright day on a high snowfield is one of the highest UV environments most people ever stand in.

What snow blindness actually is

Photokeratitis is sunburn of the cornea, the clear surface at the front of the eye. Like sunburn of the skin, it is caused by UV exposure and, like sunburn, it does not hurt while it is happening.

The symptoms turn up several hours later, typically that evening: a gritty feeling as though there is sand in the eye, pain, watering, redness, blurred vision and genuine sensitivity to light. It is temporary and the surface heals over a day or two, but for those days it is disabling, and it is entirely preventable by wearing eye protection you almost certainly already own.

Children are at higher risk, both because they have less lifetime accumulation of eye lens changes that filter some UV in adults, and for the simple practical reason that a child in a lesson spends three hours in the open and will not tell you their eyes hurt until later.

Tint and UV protection are unrelated

This is the part that matters most and is least understood. The darkness of a lens is about visible light. UV protection is a separate coating or material property, dealing with a wavelength you cannot see at all.

Read the second row. A dark lens with no UV filter is actively worse than nothing, because your pupil opens up in response to the dimmer image and admits more of the radiation that does the damage. That is the reason to check the published figure rather than judging by appearance, and it is the reason cheap novelty eyewear is a genuine hazard rather than merely a poor product.

What to check, and the good news

Look for a maker publishing 100 percent UV protection, or the equivalent phrasing of UV400, which means blocking wavelengths up to 400 nanometers. That covers UVA and UVB.

The good news is that this is not the expensive part of a goggle. Every goggle in this site’s ledger publishes 100 percent UV protection, from the most expensive adult model down to the cheapest kids frame, which publishes it alongside an anti-fog coating at the lowest price in the category. There is no reason to make a trade here and no budget at which you should.

• Check the published figure, not the tint. If a maker does not state UV protection at all, that absence is information.
• VLT is a separate number. It describes visible light and it is how you match a lens to conditions. The VLT guide covers it.
• Polarization is a third, unrelated thing. It cuts glare and says nothing about UV. The comparison is here.

Wear them all day, including the gray days

The behavior that causes most snow blindness is not skiing without goggles. It is pushing goggles up onto the helmet on an overcast morning, because there is no glare to make you want them, and leaving them there.

If the light is flat, the answer is a higher-VLT lens rather than no lens: a yellow or rose lens above about 50 percent lets in plenty of visible light while still blocking UV. The youth goggle in this ledger publishes 36% VLT, which is a deliberately middling figure chosen so that a child who owns one lens is never in the position of taking it off.

Parking goggles on a forehead has a second cost as well: warm damp skin against a cold inner lens is the classic fogging setup, which is why the anti-fog page gives the same advice for completely different reasons.

Children, specifically

• A kids frame, not a small adult one. An adult frame gaps under the cheekbones and lets reflected light in from below, which is the direction the snow is sending it. The fit guide has the checks.
• Published UV protection is the only non-negotiable specification. Everything else on a first goggle is optics rather than safety.
• Buy a spare. Goggles get lost, and the alternative to a lost goggle is a child skiing without one.
• Check they are actually wearing them. Children push goggles up when they cannot see well, which usually means the lens is too dark or the goggle is fogging.

The kids goggle roundup ranks the field on exactly these published figures, and the cheapest one on it publishes everything that matters.

Sunglasses are not equivalent

Good sunglasses with a published UV filter protect against light from in front. On snow, a large share arrives from below and around the sides, which is why goggles seal against the face and sunglasses do not. Add that sunglasses fall off, do not stop wind, and are useless in falling snow, and the full comparison lands where you would expect.

For standing around at a base area, sunglasses are fine. For a day on the mountain, goggles, and for a bright day at altitude, goggles with a published UV figure and a lens dark enough that nobody wants to take them off.