Ski Goggle Science Part 1: Light my way

May 15, 7:15 PMSkiing ExaminerEric Wagnon

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The new Fix goggle is part of the 2009-10 product line from
Scott.                                                          Photo: Scott USA

Seeing the light

Skiing a slope with any amount of confidence first requires simply seeing the slope. Light on the mountain can vary from blinding sunlight to flat light without any defining shadows. Ski goggle lenses help the eyes process visual information in these difficult conditions. How do these lenses really work? Why are certain lenses best for particular light situations? Understanding the answers to these questions requires a detour to the realm of a high-school science class.

Blinded me with science

Light is simply the eye’s interpretation of a small sliver of the electromagnetic spectrum. Going from the longest wavelength to the shortest, the spectrum includes radio waves, microwaves, infrared radiation, visible light, ultraviolet (UV) light, x-rays and gamma rays. Within visible light, the spectrum from longest to shortest wavelength makes up the familiar colors of the rainbow: red, orange, yellow, green, blue, indigo, violet.

The bronze lens in the Iris X Brown goggle from Swedish
maker POC has a VLT of 27 percent.                Photo: POC

Due to the smaller wavelength, the light on the blue end of the spectrum tends to scatter, making it more difficult for the eye to process. As a related side note, the answer to the age-old question of “why is the sky blue?” is Rayleigh scattering, the phenomenon of blue light interacting with air molecules. In overcast or snowy conditions, an overload of blue light bounces around to create what skiers call “flat light.”

ABC’s of VLT

Ski goggle lenses reduce the amount the overall light and often add one or more color tints to balance the spectrum for more contrast and definition. Visible light transmission (VLT) is the percentage of light allowed to pass through a lens. A lens designed for sunny conditions does not let in much light, so it has a low VLT percentage, generally ranging from 5 to 30 percent. A low-light or flat-light lens usually lets in much more light for VLT percentages commonly from 50 to 70 percent. A mirror finish slightly reduces the VLT.

The 2010 model of the Smith Prodigy goggles is available
with a variety of lenses.                          Photo:Smith Optics

VLT measures visible light, so it has no bearing on protection from invisible UV light. “Tinting does not affect the UV protection. Almost all goggles you buy now have UV protection,” said Dr. Eric Snyder, an ophthalmologist and avid skier.

A lens, known as photochromatic or photochromic, adjusts its VLT to the conditions. The effectiveness of photochromatic lenses is a subject of debate within the ski-goggle industry. According to Greg Randolph, communications manager at Smith Optics, his company does not offer a photochromatic lens, because the chemical process that creates the change is temperature sensitive. Randolph said the cold weather common while skiing tends to make the lenses too dark. Critics also contend that photochromatic lenses actually react to UV light and the high intensity of UV light at high altitude and reflecting off snow can make the lenses too dark for skiing.

On the other hand, Michael Jackson, co-founder of Zeal Optics, swears by the versatility of photochromatic lenses. Zeal produces a lens called the PPX, an acronym for polarized, photochromatic. The PPX has a VLT ranging from 16 to 33 percent. While even 33 percent seems rather low, Jackson said, “the visual perception feels like 65 percent, because of the polarization and tint.” The PPX combines tints of rose, brown, yellow and a neutral grey.

The Zeal PPX lens is both photochromatic and polarized.
                                                                   Photo: Zeal Optics

Zeal plans by mid-September to offer the PPX Extreme with a wider VLT range of 13 to 42 percent. “Just like snow conditions and weather conditions constantly changing, by having a versatile lens that combines photochromatic and polarization, we’ve been on the cutting edge and continue to expand on that development,” Jackson said.

Another photochromatic lens on the market is the Julbo Zebra with a VLT from 6.6 to 40.7 percent. While most ski-goggle lenses are made of polycarbonate, the Julbo Zebra lens is made of NXT, a material Julbo developed in the 1990s for the U.S. Army. Laser technology actually infuses the photochromatic dye inside the material.

Bolle produces two photochromatic lenses, the modulator citrus with an orange tint and the modulator vermillion with a reddish tint. The VLT for the modulator citrus goes from 28 to 66 percent. The modulator vermillion has a very similar VLT range of 26 to 66 percent. POC also offers a photochromatic lens in its goggle line.

With a company name derived from “ultraviolet excluded,” Uvex makes the Magic, a goggle featuring a unique way to change VLT in less than a second. The goggle has a double lens that uses liquid crystal technology to allow the switching of the lens from a high-contrast lens for flat light to a darker lens for sunny conditions. When a small electric current from a battery attached to the goggle’s head band is turned on, the liquid crystals turn dark and the VLT drops by about 30 percentage points.

Meant for sunny days, the GPS goggle line from Carrera features a gradient lens that is darker near the top of the lens. Carrera claims that the tint variation cuts down the sunlight while maximizing frontal vision.

Polarization opposites

The term “polarization” refers both to differing opinions and a lens filter that allows certain aligned light waves. In this case, both definitions are relevant, because opinions definitely differ regarding the value of polarized lenses for skiing. “It’s kind of one those personal preference things,” said Hud Knight, director of merchandising for Backcountry.com, an online retailer offering both polarized and non-polarized goggles.

The traditional view asserts that polarized lenses reduce glare more than increase contrast, so they may seem too dark in flat light. Critics also contend that polarization takes away the ability to see glare from an icy patch in the snow.

Zeal Optics SPX lens is polarized but not photochromatic.
                                                                  Photo: Zeal Optics

Several manufacturers, however, tout the benefits of polarized goggles. Oakley, in particular, has plans for increased emphasis on polarized models for next season, according to Knight.

At Zeal Optics, Jackson said the industry created “a myth that it was bad,” because manufacturing polarized goggle lenses can be an expensive, challenging process. Zeal’s lenses designed for snowsports are polarized and the majority are also photochromatic, a unique combination in the marketplace.

Uvex makes polarized lenses with Polarvision, the company’s name for a dark orange polarizer that is designed to eliminate glare but still highlight icy patches. Bolle offers a polarized brown lens with a VLT of 28 percent. Carrera manufactures polarized lenses tinted in yellow or light red.

For more, see Ski Goggle Science Part 2: Hints on tints

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