It clicks! and the clock starts running. Numbers flicker through a small display. Click again! The clock and the light meter stand still. The lens is as dark as if someone had poured black ink over it. 15 seconds of UV radiation were enough to catapult a previously clear pair of cycling glasses into "protection class 3", where sunglasses for the beach and mountains are normally found. The most efficient "self-tiners" no longer change their filter colour from light to dark grey, but from white to almost black.
Next door are the latest models with interchangeable lenses. The challenge here: changing the lenses to a tint that suits the situation should be no more complicated than putting on a crash helmet, for example. Glasses where you have to fumble around on the lens with all your fingers to change the lens and have to worry about breaking the frame are no longer in keeping with the times. With separable frames or ingenious little latches, it should finally be possible to ensure that the colourful plastic lenses supplied do not rot away unused in the case.
"Photochromatic" or interchangeable lenses - so which is the better option in 2015? One factor that helps to answer this fundamental question is the physiology of vision. The filter tint of cycling goggles not only serves to darken and thus protect against glare, but also to optimise perception. And this depends on the respective light situation. At dusk, when the colours fade, the matter is clear: untinted is best because it does not "swallow" any light. We therefore ordered the self-tinting glasses in the test with the lowest possible initial tint; most of them are practically untinted. Sunglasses are categorised into protection classes according to the European standard, depending on their light transmission. The lowest protection class, S0, extends to a darkening of 20 per cent.
If the light is brighter but very dull, yellow and orange lenses can create the illusion of greater brightness, as the eye has a particularly large number of receptors for yellow. However, the range of use for yellow lenses in particular is narrow: when the sun comes out, vision becomes harsh. Orange is less "brightening", but more versatile. Many interchangeable lens models in the test therefore have an orange lens for bad weather in the pack.
In this country, the weather is particularly often "clear to cloudy", or alternating between light and shade on the route. The ideal cycling lens for these conditions is a moderately darkening, so-called blue blocker or blue absorber. These lenses are reddish to brownish in colour. Because they filter out a large proportion of the blue light, they create a sharper visual impression with greater contrast, especially in the shade. The fact that they display many natural colours more vividly can also improve your mood. A lens of protection class S2 (57 to 82 per cent darkening) is probably the most universal lens for those who are normally sensitive to light. However, most cycling goggles come with a lens in protection class S3 as standard. With a darkening effect of 82 to 92 per cent, this is particularly suitable for bright sunshine. Neutral grey tints are common here, often with a mirror coating.
But when it comes to the colour spectrum of the lenses, the self-tinting lenses have a problem. The contrast-enhancing tints popular in cycling can hardly be achieved with photochromic lenses. With them, more or less black is simply added to the initial tint. With a clear initial tint, the result is a versatile, neutral grey, but with reddish initial tints, strange violet tones can emerge. The basis of the darkening reaction are silver compounds, the colour of which becomes visible primarily through UV radiation (intensified by low temperatures). This works well in reasonably pleasant cycling conditions, but in winter self-tinting lenses are often darker than desired, and in summer heat they may be too light. And because UV radiation is not directly linked to brightness, the dimming does not always match the rider's needs.
Added to this is the reaction time of the materials. In the UV light of the laboratory, many glasses changed from clear glass to protection class S3, which protects against bright sunlight, within 10 to 20 seconds. At room temperature, however, the return journey usually takes five to ten times as long. The new ImpactX2 lenses from Rudy Project are a surprise among the self-tinting lenses. They change from a clear lens to an increasingly intense reddish brown, which sets them apart from their grey competitors and makes them test favourites. The self-tinting lenses are generally perfect for riding at night or for an ambitiously early start to the day - they cannot react quickly to sudden changes in brightness, for example in a forest passage or a tunnel.
In view of these limitations of self-tinting glasses, anyone who prefers to adjust their glasses to the conditions themselves should definitely make the purchase decision at a specialist retailer. How practicable it is to change lenses is also determined by the practice in the shop. It should be possible to change the lenses on the right model without having to clean the glasses afterwards. And it should work so smoothly that you can trust the mechanism to handle many, many lens changes. The quality of this mechanism is a key argument in the battle between the two types of glasses. The price, on the other hand, takes a back seat: a good pair of glasses with three interchangeable lenses enclosed need not be more expensive than one with a single, self-tinting lens.
The complete article was published in Trekkingbike issue 5/2015.
You can download the individual articles as PDF files here.
