Alexzn's Googles 101
So, you want to buy a new pair of goggles? Go to the store (or the your favorite online retailer), take a look at the boxes, or at the product page of the pair that you like. Admire the artfully written copy and carefully constructed diagrams of traced and split color rays. Take a deep breath. Most of this stuff is at best irrelevant and at the worst wrong. There are only two characteristics of a google that should matter to you, and one of them is almost never even mentioned in those descriptions. (There is also a third important parameter-fit-but we will talk about that later).
The first parameter is VLT- Visible Light Transmission- number, which tell you how dark the lens is. Usually it is expressed as a percent of light that passes through the goggle. A VLT of 8 will be a very dark lens that transmits only 8% of the visible light, suitable only for very bright days, and a VLT of 70 will be a "storm" type lens that passes almost all the light through. Normal general-purpose lenses usually have VLTs at around 30 (20-40%), storm lenses tend to be at 60-85 VLT and really bright sunlight lenses are at 20 and below. If you can afford only one pair of goggles, it should be a general purpose lens, your second pair should be a storm goggle. Many manufacturers sell goggles with two lenses included, and in most cases it will be a general purpose lens coupled with a storm lens.
Technical aside 1: Why do goggle lenses need to attenuate the light? Our eyes can detect well only a certain range of light intensities. When the contrast in a scene (the absolute difference between the bright and dark regions) is too high, the eyes stop seeing details in some of those regions. Cutting out a portion of the light preserves the relative intensity differences, but reduces the absolute value of the difference. Suppose, an eye can only differentiate between the values that are at most 1,000 units apart and we are looking at a scene with the sky at 2000 units brightness and shadows in front of bumps that are at 200 units. The contrast value of 1800 units is too much for the eye to handle, and as the result you don't see any details in those shadows. Now lets put on a google with a VLT of 20. Now we see the sky at 400 units and the shadows at 40 units. We now cut the contrast to 360 units, well within our initial 1,000 units "dynamic range" value. The eye can adjust to the reduced brightness and perceive the full contrast range of the scene.
The second parameter is the lens material. This is something that manufacturers don't tell you, or if they do, they wrap it in impenetrable language of proprietary trade and marketing names that feels and sounds like cryptonite. Ptutonite, SR93, ChromaPop, Prizm, NXT, the list does on and on. In reality, an overwhelming majority of the lenses are made of only three materials. The cheapest googles are made for some sort of acetate polymer (those are the goggles where the lens is so thin that you can deform it with your fingers). That material is soft, easy to scratch, and has mediocre optical properties (this is why they have to make it so thin). Those google should only be bought as emergency throwaway replacements, if possible, so go for the better lens materials if you can afford it. By far the most common good goggle lens material is polycarbonate, which is a standard material for any sports - related optics. Every company, Oakley, Smith, Briko, POC, Zeal, etc. uses polycarbonate and calls it something else. It's a great material, clear, scratch-resistant, and light. A newer, and by all accounts better, lens material is Trivex, which has been popularized by the advent of rimless eyeglasses. It is significantly clearer (in fact as clear as glass), and just as scratch-resistant and shatter-proof as polycarbonate. So far only few companies use it in their higher-end goggles and nobody calls it Trivex. POC's NXT and Smith's ChromaPop lenses are Trivex. Anecdotally, all Kaenon's sunglasses have Trivex lenses, as well. If you afford a Trivex lensed google, I highly recommend it, the clarity difference would be noticeable.
Technical aside 2: Why is Trivex Better? One of the key materials characteristics is its propensity to disperse the light of different color, which makes the features slightly blurry. Its is measured by the so-called Abbe number (the higher it is, the better the material is optically). The gold standard is glass with Abbe number of 42. Polycarbonate clocks in at 30, Trivex has the Abbe number of 43, virtually indistinguishable from glass. Some glasses such as crown glass, have even higher Abbe value of 59. Curiously, a common eyeglass lens plastic CR-39 has an Abbe value of 58, but, unfortunately, it is not considered shatterproof (at least I have not heard of goggle lenses made of CR39). One advantage polycarbonate has over Trivex is that it has a higher index of refraction, allowing for thinner eyeglass lenses, but that is irrelevant for nonprescription sunglasses or goggles.
Lens tints. There is no other area that is so full of misconceptions and outright BS as lens tints. Every company claims to have a proprietary lens tint that increases contrast and give you magical powers to see through the fog, behind bumps, and right through the soul of your fellow skier. Most is just marketing hot air. The overwhelming majority of the lenses have reddish-yellow tint that is designed to remove light in the blue region of the spectrum and increase contrast (see Technical Aside 3 to why this works). The game is finding a compromise between maximizing contrast enhancement and minimizing overall color distortion at a given VLT. Smith and POC prefer to compromise on amber/sienna tints. Oakley recently went all out to the "more contrast" camp by coming out with the Prizm tints that are all VERY red. in general VLT and the lens material are much more important for the overall experience than the tint. (Note- never judge the tint from how the goggles look, always look THROUGH them. Mirror coatings are sometimes used to drop VLT further down, but usually they are there for aesthetic purposes, i.e. to make your goggle look cool).
Technical aside 3: A single physical law is responsible to why the sky is blue and military tactical lights are red. The Rayleigh law says that the scattering efficiency of the light is inversely proportional to the 4th power of wavelength, which means that blue light scatters much more than red. This is why military uses red lights to read maps, to minimize the scattered light that can be picker up by an enemy. Scattered light robs a scene from contrast, this is why most goggle lenses are reddish. Red tints also darken the sky to reduce distraction for a skier. I suspect that this is all there is to the Oakley's Prizm technology. It is simple, but it works.
Photochromatic lenses. Photochromatic lenses are lenses that change their VLT depending on the light conditions. This is desirable property that stretches the versatility of a google lens. POC NXT lenses are photochromatic with VLT that goes from 10-50. This is what I have, and although I have a dedicated (polycarbonate) storm lens, I all but stopped using it. The combination of convenience of adjustable VLT and increased clarity from Trivex makes it work well enough in every light conditions, and if the weather changes from foggy to sunny, I don't have to worry about switching goggles. Zeal also makes photochromic goggles. Smith makes photochromatic sunglasses, but I do not think they make photochromatic google lenses. One drawback is that tint adjustment takes time; thus, if you dive into dark trees form a sunny ridge, the lenses cannot adjust fast enough.
Polarized lenses. Unlike hiking, fishing, sailing, hunting, or driving sunglasses where polarized lenses are desirable, skiing derives very little functional benefit from polarized lenses. The reason is that snow is composed of billion of tiny randomly-oriented ice crystals that scramble polarization of the reflected light. Polarized goggles ill still darken the sky and reduce reflections from foliage, but they would do nothing for the snow contrast. Don't waste your money.
Goggle fit. This is a key point that a lot of people miss. If you wear a helmet (you should), buy the helmet first and then make sure that the goggle you buy fits your helmet in a way that there is no gap between the top of the goggles and a helmet (if you ever heard the term "gaper gap", this is it. Make sure also that the goggle does not pressure your nose and that the gap with helmet on the sides is not too big.
Classic gaper gap
Interchangeable lenses or separate goggles? Last few years saw a trend of manufacturers including an extra lens with their higher end googles and making the lens change much easier. It arguably started with Smith I/O goggles which promised (and delivered) easy lens changes in minutes for everyone. Arguably the coolest solution is Anon's M2/M3 googles where the lenses are held to the frame with 8 powerful rare earth rare earth magnets and can be changed in seconds. I am personally split on the utility of this approach, I would much rather just carry a second pair of goggles with me instead of messing around with lens switching on the lift, but many people like the increased compactness of having to carry only a lens in their pockets. A photochromic lens made it a mute point.
Sunglasses or goggles? Many people ski in sunglasses because googles are too hot on a sunny day. Its a personal choice, but I would not recommend it for the following reasons:
Durability and failure modes. Aside from crash damage the most common failure mode of goggles has nothing to do with lenses, they usually are retired when the face foam degrades, when the strap gets stretched too much and loses elasticity, of when the lens gets too many scratches. Another common mode is when the seal between the inner and outer lens sheet fails and moisture gets in between the lenses, giving rise to a royal size fogging issues. Smith's unique Porex filter design that they use in their lenses seems to be more effective in reducing those incidents, but other companies are usually very good at warranting this type of failure. Contrary to the conventional wisdom goggles are usually scratched when you not skiing, so keep them in a protective bag in your backpack and don't throw them on the lunch table.
Happy (and clear-eyed) skiing!
So, you want to buy a new pair of goggles? Go to the store (or the your favorite online retailer), take a look at the boxes, or at the product page of the pair that you like. Admire the artfully written copy and carefully constructed diagrams of traced and split color rays. Take a deep breath. Most of this stuff is at best irrelevant and at the worst wrong. There are only two characteristics of a google that should matter to you, and one of them is almost never even mentioned in those descriptions. (There is also a third important parameter-fit-but we will talk about that later).
The first parameter is VLT- Visible Light Transmission- number, which tell you how dark the lens is. Usually it is expressed as a percent of light that passes through the goggle. A VLT of 8 will be a very dark lens that transmits only 8% of the visible light, suitable only for very bright days, and a VLT of 70 will be a "storm" type lens that passes almost all the light through. Normal general-purpose lenses usually have VLTs at around 30 (20-40%), storm lenses tend to be at 60-85 VLT and really bright sunlight lenses are at 20 and below. If you can afford only one pair of goggles, it should be a general purpose lens, your second pair should be a storm goggle. Many manufacturers sell goggles with two lenses included, and in most cases it will be a general purpose lens coupled with a storm lens.
Technical aside 1: Why do goggle lenses need to attenuate the light? Our eyes can detect well only a certain range of light intensities. When the contrast in a scene (the absolute difference between the bright and dark regions) is too high, the eyes stop seeing details in some of those regions. Cutting out a portion of the light preserves the relative intensity differences, but reduces the absolute value of the difference. Suppose, an eye can only differentiate between the values that are at most 1,000 units apart and we are looking at a scene with the sky at 2000 units brightness and shadows in front of bumps that are at 200 units. The contrast value of 1800 units is too much for the eye to handle, and as the result you don't see any details in those shadows. Now lets put on a google with a VLT of 20. Now we see the sky at 400 units and the shadows at 40 units. We now cut the contrast to 360 units, well within our initial 1,000 units "dynamic range" value. The eye can adjust to the reduced brightness and perceive the full contrast range of the scene.
The second parameter is the lens material. This is something that manufacturers don't tell you, or if they do, they wrap it in impenetrable language of proprietary trade and marketing names that feels and sounds like cryptonite. Ptutonite, SR93, ChromaPop, Prizm, NXT, the list does on and on. In reality, an overwhelming majority of the lenses are made of only three materials. The cheapest googles are made for some sort of acetate polymer (those are the goggles where the lens is so thin that you can deform it with your fingers). That material is soft, easy to scratch, and has mediocre optical properties (this is why they have to make it so thin). Those google should only be bought as emergency throwaway replacements, if possible, so go for the better lens materials if you can afford it. By far the most common good goggle lens material is polycarbonate, which is a standard material for any sports - related optics. Every company, Oakley, Smith, Briko, POC, Zeal, etc. uses polycarbonate and calls it something else. It's a great material, clear, scratch-resistant, and light. A newer, and by all accounts better, lens material is Trivex, which has been popularized by the advent of rimless eyeglasses. It is significantly clearer (in fact as clear as glass), and just as scratch-resistant and shatter-proof as polycarbonate. So far only few companies use it in their higher-end goggles and nobody calls it Trivex. POC's NXT and Smith's ChromaPop lenses are Trivex. Anecdotally, all Kaenon's sunglasses have Trivex lenses, as well. If you afford a Trivex lensed google, I highly recommend it, the clarity difference would be noticeable.
Technical aside 2: Why is Trivex Better? One of the key materials characteristics is its propensity to disperse the light of different color, which makes the features slightly blurry. Its is measured by the so-called Abbe number (the higher it is, the better the material is optically). The gold standard is glass with Abbe number of 42. Polycarbonate clocks in at 30, Trivex has the Abbe number of 43, virtually indistinguishable from glass. Some glasses such as crown glass, have even higher Abbe value of 59. Curiously, a common eyeglass lens plastic CR-39 has an Abbe value of 58, but, unfortunately, it is not considered shatterproof (at least I have not heard of goggle lenses made of CR39). One advantage polycarbonate has over Trivex is that it has a higher index of refraction, allowing for thinner eyeglass lenses, but that is irrelevant for nonprescription sunglasses or goggles.
Lens tints. There is no other area that is so full of misconceptions and outright BS as lens tints. Every company claims to have a proprietary lens tint that increases contrast and give you magical powers to see through the fog, behind bumps, and right through the soul of your fellow skier. Most is just marketing hot air. The overwhelming majority of the lenses have reddish-yellow tint that is designed to remove light in the blue region of the spectrum and increase contrast (see Technical Aside 3 to why this works). The game is finding a compromise between maximizing contrast enhancement and minimizing overall color distortion at a given VLT. Smith and POC prefer to compromise on amber/sienna tints. Oakley recently went all out to the "more contrast" camp by coming out with the Prizm tints that are all VERY red. in general VLT and the lens material are much more important for the overall experience than the tint. (Note- never judge the tint from how the goggles look, always look THROUGH them. Mirror coatings are sometimes used to drop VLT further down, but usually they are there for aesthetic purposes, i.e. to make your goggle look cool).
Technical aside 3: A single physical law is responsible to why the sky is blue and military tactical lights are red. The Rayleigh law says that the scattering efficiency of the light is inversely proportional to the 4th power of wavelength, which means that blue light scatters much more than red. This is why military uses red lights to read maps, to minimize the scattered light that can be picker up by an enemy. Scattered light robs a scene from contrast, this is why most goggle lenses are reddish. Red tints also darken the sky to reduce distraction for a skier. I suspect that this is all there is to the Oakley's Prizm technology. It is simple, but it works.
Photochromatic lenses. Photochromatic lenses are lenses that change their VLT depending on the light conditions. This is desirable property that stretches the versatility of a google lens. POC NXT lenses are photochromatic with VLT that goes from 10-50. This is what I have, and although I have a dedicated (polycarbonate) storm lens, I all but stopped using it. The combination of convenience of adjustable VLT and increased clarity from Trivex makes it work well enough in every light conditions, and if the weather changes from foggy to sunny, I don't have to worry about switching goggles. Zeal also makes photochromic goggles. Smith makes photochromatic sunglasses, but I do not think they make photochromatic google lenses. One drawback is that tint adjustment takes time; thus, if you dive into dark trees form a sunny ridge, the lenses cannot adjust fast enough.
Polarized lenses. Unlike hiking, fishing, sailing, hunting, or driving sunglasses where polarized lenses are desirable, skiing derives very little functional benefit from polarized lenses. The reason is that snow is composed of billion of tiny randomly-oriented ice crystals that scramble polarization of the reflected light. Polarized goggles ill still darken the sky and reduce reflections from foliage, but they would do nothing for the snow contrast. Don't waste your money.
Goggle fit. This is a key point that a lot of people miss. If you wear a helmet (you should), buy the helmet first and then make sure that the goggle you buy fits your helmet in a way that there is no gap between the top of the goggles and a helmet (if you ever heard the term "gaper gap", this is it. Make sure also that the goggle does not pressure your nose and that the gap with helmet on the sides is not too big.
Interchangeable lenses or separate goggles? Last few years saw a trend of manufacturers including an extra lens with their higher end googles and making the lens change much easier. It arguably started with Smith I/O goggles which promised (and delivered) easy lens changes in minutes for everyone. Arguably the coolest solution is Anon's M2/M3 googles where the lenses are held to the frame with 8 powerful rare earth rare earth magnets and can be changed in seconds. I am personally split on the utility of this approach, I would much rather just carry a second pair of goggles with me instead of messing around with lens switching on the lift, but many people like the increased compactness of having to carry only a lens in their pockets. A photochromic lens made it a mute point.
Sunglasses or goggles? Many people ski in sunglasses because googles are too hot on a sunny day. Its a personal choice, but I would not recommend it for the following reasons:
- Modern goggles are vented very well. (As an aside, the rather "drafty" nature of the Smith I/O design probably contributed to their popularity as much as their pioneering design, because it virtually eliminated fogging).
- Sunglasses have a decidedly lower speed limit than googles. At higher speed your eyes will start tearing up if you wear sunglasses.
- Goggles are designed to protect your nose and face in a crash. Sunglasses frames can break and injure your face or eyes in a crash.
- Goggles have double lenses that reduce fogging. If you crash in sunglasses and get snow to cool the inside surfaces of your lenses, they will start fogging like crazy.
- Sunglasses may have glass lenses. Do NOT ski in glass-lensed sunglasses! Ditto for cheap sunglasses which may be made from wonderfully clear CR39 plastic which is NOT shatterproof.
Durability and failure modes. Aside from crash damage the most common failure mode of goggles has nothing to do with lenses, they usually are retired when the face foam degrades, when the strap gets stretched too much and loses elasticity, of when the lens gets too many scratches. Another common mode is when the seal between the inner and outer lens sheet fails and moisture gets in between the lenses, giving rise to a royal size fogging issues. Smith's unique Porex filter design that they use in their lenses seems to be more effective in reducing those incidents, but other companies are usually very good at warranting this type of failure. Contrary to the conventional wisdom goggles are usually scratched when you not skiing, so keep them in a protective bag in your backpack and don't throw them on the lunch table.
Happy (and clear-eyed) skiing!
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