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Sports technology: Ski goggles

One pair of ski goggles for all conditions - is it possible?

For anyone indulging in winter sports, perhaps their most important piece of equipment will not be their skis or snowboard, but the correct eyewear - after all, if you can’t see where you’re going you can’t do much.

Eye protection is essential against sub-zero temperatures, blowing snow and the intense rays of the sun at high altitude and when bouncing back off snow and ice. Snow blindness, or photokeratitis, whilst rarely permanent, is nevertheless extremely painful and will bring your holiday to a grinding halt.

The Inuit developed the earliest method of dealing with the problem by using ‘goggles’ carved from reindeer antlers - they had a thin slit through which the wearer could see and prevented excessive levels of ultraviolet light harming the eyes. In an emergency, a similar method of protection can be used by cutting slits in dark fabric placed across the eyes, or at worst - and as recommended by ancient Egyptians and the SAS - blackening the skin beneath the eyes to reduce reflection.

Modern snow goggles are considerably more comfortable and sophisticated than those of the Inuit, usually having twin lenses as developed in the 1960s by Robert Earl Smith of Smith Optics. This prevents the ‘fogging’ that occurs with a single lens when interior water vapour condenses onto the cold lens - with a double lens the inner lens remains warm enough to prevent condensation.

Most ski goggles, especially more high-end models, come with various lenses which have different tints for different light conditions, but what happens if the weather changes whilst you’re on the mountain? A lens designed for bright, sunny conditions will be far less effective in a snow storm and vice-versa, after all.

Well, you could carry a spare pair, or use goggles with a feature such as the excellent ‘Swiftlock’ system used by Dragon Goggles, which involves flicking up a small switch on either side of the frame, taking out the lens, dropping in a replacement more suitable to the conditions and locking down the switch again.

Or you could simply go for goggles with photochromic lenses, which darken on exposure to UV radiation, so that they are clear in low ambient light conditions but dark in bright sunlight. For example, one manufacturer makes a lens with transmittance reducing from 87 per cent to 20 per cent and another which reduces from 45 per cent to 9 per cent.

Photochromic lenses were developed in the 1960s and made from glass that contained silver-based chemicals which clump together when light falls on them, causing the lens to darken.

Modern photochromic lenses are made of polycarbonate or plastic for obvious safety reasons, and instead of silver chemicals that clump together, they contain carbon-based molecules that change their colour and size in ultraviolet light, reducing the amount of light passing through the lens.

Most manufacturers now offer one or more models with photochromic lenses. Examples include the well-regarded Julbo Zebra and Bollé Gravity, while new for this season is the Nike Transition range of ski goggles, designed after collaboration between Nike and Transitions Optical, who specialise in photochromic lenses.

The goggles are not cheap at £249.90, but they do obviate the cost of buying more than one pair of fixed-tint goggles or a range of interchangeable lenses.

John Ligas, vice president for research and development at Transitions Optical, explains how Nike Transitions adaptive lenses self-adjust from a yellow base tint at night to mid-tint in low light conditions and to dark grey in bright sunlight. “The activation you see is caused by a chemical reaction in the photochromic molecules embedded in our products which allows the lenses to seamlessly change tint in reaction to UV light. The molecules absorb energy from the sunlight, causing a carbon-oxygen bond to break. The molecules re-arrange to the open form, now absorbing not only in the UV region, but also in the visible light region, where colour can be seen.

“When the UV light is removed, such as when a skier goes indoors or at night, thermal energy causes the photochromic molecules to rearrange back to the original form of the colourless state.”

The photochromic dyes are formulated to provide different colours when activated, to suit the desired activity.

Ski-goggle lenses are categorised from 0 to 4. The higher the number, the darker the tint. Category 2-3 are the best all-round option, category 4 is only for the brightest conditions, such as high-altitude glaciers, whilst category 0 is for night skiing and indoor slopes.

Ligas points out that Transitions Optical’s core product development is clear-to-dark prescription spectacle lenses, but Nike approached the firm because it wanted to upgrade its fixed-tint products with photochromic technology.

“We started with our core technology that is used for producing Transitions lenses for the ophthalmic lens market. In order to treat the larger goggle surfaces rather than typical round lenses, we altered the coating formulation and application technique, but used the same photochromic dyes adjusted for the fixed tint of the initial colour of the goggles.”

However, the dyes had been formulated for sports goggles used in normal cool to hot weather conditions, so they had to be modified to reach “peak optimised performance” at temperatures around freezing.

This effectively means that a skier need only have one pair of goggles for any conditions they’re likely to come across, even blizzards, as Ligas explains.

“Certainly we believe that one of the key benefits to our product is that it eliminates the need to carry two pairs of goggles or change your goggle lenses throughout the day depending on light conditions. Typically in blizzard conditions, the sunlight, and therefore the UV light, is much filtered or blocked by the severe weather, but the same principles apply.”

The activation time of all photochromic products is based on several factors, including altitude, latitude, strength of the sun, time of day, direction of the wearer in relation to the sun, amount of UV light present and temperature.
The level of darkness depends on the balance between the UV-driven activation reaction and the temperature-dependent fade reaction.

A standard photochromic ophthalmic lens will typically change from yellow to full grey in a matter of minutes, but the colder it is and the more direct sunlight the lens receives, the faster the lens will activate and stay activated. Therefore, because UV levels are higher whilst skiing due to increased altitude and the reflective surface of snow, ski-goggle lenses react much more quickly than those of regular spectacles.

At first glance, photochromic lenses may appear to be a bit of a gimmick - after all, how long does it take to change your goggles or lenses? However, ski professionals, such as Icelandic mountain guide Jökull Bergmann, are convinced of their efficacy.

“I have been using the Julbo Aerospace goggles [which have photochromic lenses] recently and I must say that it’s quite revolutionary not having to deal with changing lenses. I have most definitely made the transition to one-lens technology whether I’m leading clients or skiing recreationally”.

I have skiied with Jökull in the past on the wild, mountainous terrain of Iceland’s Troll Peninsula, and I can say that if photochromic lenses are good enough for him, then they’re certainly good enough for recreational skiers like me. It seems likely that the majority of keen skiers and boarders will switch to this technology in the future when they buy new ski goggles.

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