2020 vision
Sunglasses are about more than just protecting your eyes from the sun
Picture the scene: your midwinter Sunday morning has dawned still and crisp. Low, piercing sunlight shines down from a bluebird sky. Your choice of eyewear is easy because your regular, iridium-coated, high-contrast sunglasses will shade your eyes. But what about when the weather changes?
Cloud, drizzle and low light create uncertainty. Will normal sunglasses help or hinder? Is a different coloured lens required? Should you use a clear lens? Or maybe even ride with no shades at all? When it comes to that last point, the experts we talked to at Oakley, 100% and Roka are all in agreement.
‘I’d always suggest wearing a pair of sunglasses even in really murky conditions,’ says Tatiana Kalache,
R&D project manager at Oakley. ‘It’s impossible to manufacture light, but low-light lenses boost contrast with little ambient light, and even with a clear lens your eyes are still getting the physical protection of the glasses as well as 100% UV protection.’
It’s in a sunglasses manufacturer’s interest to recommend that riders wear more sunglasses more of the time, but the rationale is sound. Anouk Willmen, eyewear product manager at 100%, explains further. ‘Each colour has its own wavelength. By blocking out certain wavelengths we change which colours reach the eye and thus change what you see. By carefully formulating the base tints of our lenses, combined with the mirror coatings, we are able to filter specific colours to create a more vibrant perception with higher contrast and better depth.’
Base tint formulation is a rather tricky game to master, however, relying on experience and labs full of sophisticated hardware.
‘One piece of field equipment we use is called a hyperspectral camera,’ says Kalache. ‘It tells you which wavelengths are reflecting off what surfaces, which is useful because then we know what we need to filter to create contrast – particularly on road surfaces because they’re typically quite dark in that they absorb a lot of light. We do that by creating a recipe of our Prizm dyes and lens coatings. Between them they precisely absorb the wavelengths that would obscure the detail in a surface.’
‘You’ll see the term VLT mentioned in this regard,’ adds Willmen. ‘It stands
for “visual light transmission” and explains how much light a lens lets through to the eye. Our HIPER Coral lens, for example, passes 52% of the incoming light while ramping up contrast because of its base colour formula. Higher VLT figures suit murkier conditions.’
The dyes and coatings are typically mixed in and applied to some form of polycarbonate or nylon.
‘ We choose nylon for its premium optics, light weight, chemical and stress resistance, and impact properties,’ says David Ginther, VP of engineering at Roka. ‘ Polycarbonate is used for models requiring a very specific impact standard.’
Even lens shape plays its part in optical clarity. ‘Spherical’ lenses were common when glasses were highwrap, small frames with dual lenses.
‘Spherical lenses have a uniform base curve in all directions,’ says Ginther. ‘As sunglasses have trended towards bigger, flatter, shield-like lenses, the “toric” shape has become more common. These have a different base curve along the horizontal and vertical axes. We think the shape allows for an optimised field of vision.’
Kalache says Oakley agrees. ‘ Some of our newer designs, like the Sutro glasses, use a cylindrical shape, which is curved horizontally but flat vertically.’
100% is a big proponent of the cylindrical shape lens. ‘ Coming from the dirt bike goggle industry we wanted to keep that bold, oversized statement design,’ says Willmen. ‘Our frames are quite big so we don’t need a spherical or toric lens to get great coverage.’
Seeing clearly
Tint, VLT and shape aside, many performance lenses are now treated as standard with anti-fog, hydrophobic (water-repelling) and oleophobic (oilrepelling, like finger smudges) coatings. Sunglasses can also include polarised lenses or photochromic lenses that darken when exposed to bright light, although both these technologies can have their downsides.
‘ Polarised lenses cut glare,’ says Kalache. ‘When light wavelengths hit a reflective surface they bounce back off it horizontally, which causes glare. Imagine polarised lenses like a picket fence. Normal vertical light wavelengths can pass through to your eyes, but the horizontal wavelengths are blocked. We intentionally don’t make Prizm lenses polarised because we believe glare might be a cue for a slick surface that you need to avoid.’
Oakley takes a similarly measured stance when it comes to photochromic lenses: ‘UV triggers photochromic lenses to adjust their tint, but we still think the tech has a way to go. The swing rate from light to dark is too slow for cyclists flitting in and out of shade at speed, but we’re always looking at how to improve things,’ says Kalache.
‘Photochromic’s price is a barrier, as is its appearance. Photochromic lenses aren’t as cool as mirrored,’ says Willmen. ‘ But if you don’t want the hassle of swapping lenses or you’re using them on a day with variable light conditions they can be great.’
There is clearly so much more to sunglasses than meets the eye, and plenty to consider when choosing a pair. But find the right ones and they can turn another grey day into a ride filled with technicolour wonder.
‘Photochromic lenses aren’t as cool as mirrored, but if you don’t want the hassle of swapping lenses they can be great’