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Choosing goggles and glassesUVA, UVB, anti-reflective coating, polarised lenses: we have all read these words on the packaging of goggles and glasses, without really knowing what they meant. Ski time has attempted to shed light on these opaque optical terms, which nevertheless are vital for protection of our eyes, because we can always buy a new pair of goggles or glasses, but not new eyes.
Knowing the risksThe sun is the biggest (visible) source of light on earth, but also a powerful (invisible) source of electro-magnetic energy. The human eye picks up less than 40% of solar energy. This visible light is made up of all the light waves whose length falls between 380 and 780 nanometres (1 nm = 0.0000001 metre). Those which fall between 380 and 500 nm are potentially dangerous because, according to a recent theory, the eye cannot visualise these colours as accurately as the others and the blur damages the retina. 60% of solar energy is made up of rays that are invisible but which are still absorbed by the eyes. INFRA-RED rays account for 55%. They are thermal heat-bearing rays and correspond to all light waves above 780 nm). In normal conditions, the eye can tolerate this type of ray without problems. The remaining 5% are ULTRA-VIOLET rays (UVB and UVA), which are the most harmful (their light waves are lower than 380 nm). They contain more energy than light, so it is dangerous for the eye to absorb them. For example, the action of UV rays combined with the wind, which dries the eyes, can cause snow blindness, but also cataracts, retinal disorders, ophthalmia, and other problems. The harmful effects caused by the different UV rays build up as the years go by and are irreversible. Similarly, some people are more sensitive than others to UV rays or can become sensitive over time. UV rays are mainly absorbed by the ozone layer, and we all know what state that is in… They are present even in cloudy conditions (50% of UV rays reach us even when there is thick cloud cover) and 85% are reflected by snow (compared to 20% by water). Furthermore, their intensity is also affected by altitude: the amount of UVB increases by 4% every 300 m. For example, the reflection at an altitude of 2800 metres is 32% greater than at 400 metres.
The different lens coatings
Lenses and colour filters undergo different processes to give them specific properties:
- ANTI-UV COATING: UV absorbers are applied to the lenses, by dip-coating. People often think that dark lenses protect against UV rays. Wrong. The colour of the lens merely serves to provide comfort against dazzling. A dark lens without coating increases the harmful effects of UV rays: they penetrate even further because the pupils are dilated for greater visibility!
- ANTI-REFLECTIVE COATING (also called iridium coating): this is a lens-coating designed to prevent dazzling. It decreases dazzling caused by the reflection of rays from a flat surface toward the eyes. The coating is applied using a high-temperature process in which metal deposits (often chrome) are sprayed on under vacuum. The deposit is applied in single layer or in several layers. The more layers there are, the more efficient the coating will be. It aims to reduce the intensity of “ghost images” but is extremely sensitive to scratching.
- Today, you often hear talk of POLARISED lenses or colour filters, which are especially suitable for snow or water (surfaces on which reverberation is at its highest). They lessen reflection of light to eliminate dazzling. How does it work? Light vibrates both horizontally and vertically except when it is reflected off a surface. Afterwards, the light only vibrates horizontally. Polarised lenses have a filter which cuts off the dazzling horizontal vibrations. Its principle is as follows: a thin layer of polarised plastic (a filter) is uniformly laminated between the two faces of the lenses or colour filters, so that it forms a barrier that prevents reflected light from penetrating into the eye. How can you tell if the lenses or colour filter are polarised? Turn it over above a digital watch (with an LCD display). If at certain angles the display disappears, then the lens is polarised.
- ANTI-SCRATCH COATING: Plastic lenses (in organic plastic, resin or polycarbonate), just like colour filters, are light and resistant but extremely sensitive to scratching. Therefore, anti-scratch coating, which improves resistance to scratches and friction, is either sprayed on under vacuum, deposited by centrifuging, moulded into the lens or applied by dip-coating. Dip-coating seems to be the best technique, because it produces a thicker and therefore more efficient layer.
- WATER-REPELLENT COATING: This is an outer coating which repels water, helping it to flow over and slide off lenses and colour filters without leaving traces and providing constantly impeccable vision.
- WATER-ATTRACTING COATING: This is an inner coating which absorbs moisture, and helps prevent condensation. Similarly, anti-dirt coatings exist which prevent impurities or grease from stagnating on the filter or the lens.
- ANTI-DISTORSION COATING: Today, all colour filters are “double-layered”, i.e., they are more efficient in combating condensation because air can circulate freely between the two layers. However, they are more sensitive to the effects of distortion than single-layer filters. Many manufacturers have tried to solve this problem, with results of varying efficiency. Try on the glasses (or goggles) and look at a rectangular object. If the lines stay straight when you move your head up and down and from left to right, then the distortion effect is limited.
Different shades
Since 1995, a European standard has set out the minimum level of protection to be provided by sun lenses concerning the extent to which they filter light. Their scale ranges from 0 to 4. Category 0 lets through almost all light, whereas class 4 absorbs it completely. People exposed to the sun for long periods and to reflective surfaces should wear lenses which let through only 15% of light or less, i.e., category 3 or 4 lenses. Plastic lenses allow the widest variety of shades, because they are surface-coloured by dip-coating in a suitable tint. Each colour of lens and filter has its own specific characteristics, and affects our vision differently. If you take these properties into consideration, it is possible to find the most suitable eyewear: |
- GREY. This shade is often used, because it accurately reproduces colours, without altering natural vision. In general, the protection indexes vary from 3 to 4, depending on whether the colour has a dark tone or not. Grey is therefore recommended for intense sunshine, snow and glaciers.
- BROWN. Shades of brown (extending to almost golden) are also often used. The have some advantages that shades of yellow boast, in that they also absorb blue light. They produce warm and pleasant tones, increase contrasts in sunny conditions, but slightly alter colour perception. In general, these lenses or colour filters are category 3 or 4 depending on whether they have a dark or light tone.
- GREEN. Green colours provide a transmission curve which is very close to that of the human eye. They improve colour perception with reinforcement of natural green tones. Generally equivalent to a protection index of 3, they can be used for sunny days because they also protect against dazzling.
- YELLOW-ORANGE. They give a highlight effect and increase contrasts in foggy conditions, or as daylight is fading, but tend to alter the portrayal of colours. They are also able to absorb blue light. They usually have protection indexes of 1 to 2. They are therefore not recommended for intense sunshine.
- PINK. Shades of pink are often used in situations where lighting is poor, because they provide increased brightness. Only light shades of pink are used, since dark pinks alter perception of colours, which causes visual discomfort. They have a protection index of 1 to 2.
- TRANSPARENT - COLOURLESS. This type of eyewear only provides protection against projectiles and wind. They are recommended for use against artificial light or for night skiing. Their protection index is 0 and they absorb hardly any light at all.
- BLUE, PURPLE AND RED. In general, these shades of colour do not provide any benefits.
Choosing the right outfit
Materials
- Outer fabrics
This is most important for appearance, but certain technical characteristics must not be neglected. For example, it must be water repellent. Even though water-repellence relies on chemical treatment of the fabric, different treatments may not all react in a similar way to the rain and may vary in their rain-proof efficiency.
- Membranes
Some membranes are benchmarks in the field, such as Gore-Tex, but today, most brands develop there own membranes. It is therefore essential to gauge the impermeability of these membranes and their breathability, i.e., whether they provide adequate protection against heat stress.
- Linings
The lining should be adapted to the other fabrics of your outfit It is the main source of heat for your ski jacket, so you need to choose your outfit in accordance with how you intend to use it. Some lining fabrics are especially worthy of note, like Thinsulate for example.
The fine points
- Zips
Zips can vary in just how technical they are. The best zips are waterproof zips, because they give perfect insulation, but they are sometimes difficult to open. Suitably sized pull tabs are necessary, so that you can open your pockets without taking off your gloves.
- Fasteners
For optimum insulation, you need to be able to adjust your jacket. At the wrists, you need to be able to tighten the end of your sleeves once you have put your hand through. A good fastening collar is also desirable to avoid air or snow going down your neck when riding.
- Aeration
Depending on their size, location and whether they are fitted with netting, they should provide more or less satisfactory ventilation. They should also be adapted to your various outfits and different ways in which you will use them. For example, if you want to go hiking, you will need fairly large ventilation. The same is true for padded jackets.
- Seams
Today, heat-sealed or thread-free seams are common. In such cases, the fabric is not pierced, providing maximum waterproofing. The collar It all depends on the cut: it should hug the body with out being too tight, allowing you to add layers underneath.
- Wrists
The best way to protect your arms is to use Lycra glove sleeves with holes for your thumbs. The Lycra allows good freedom of movement, whilst preventing your sleeves from riding up and allowing the snow to enter.
- Connections
To provide even greater waterproofing for your outfit, today brands produce systems that allow you to zip your jacket to your ski trousers. Once attached, it is like being in a ski-suit, without the old school touch. Some brands even sell garments in Lycra that can be zipped together for even greater freedom of movement.
- Strong points
They are not vital, but the extra comfort is always a plus. The Recco system is a good idea, even if it is better to avoid having to use it: it is a passive reflector which helps you to be located if trapped under snow. Other items are also very practical: hooks for fastening your gloves when not using them, a chamois cloth in your pocket to wipe your goggles clean, special pockets for MP3 players with holes for earphones, a transparent window on your sleeve for checking the time without taking off your jacket, a bottle opener, etc. Each to their own.
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