How much light transmission at a given elevation?

I have done some searching to see how much light transmission is ok at a certain elevation for your eyes, but can't come up with a comparison or chart. I see where "mountain climbers" need 5% to 8% light transmission in glacier glasses/sun glasses, but would like a chart or comparision table for any given elevation. I just found out, that permissible light changes by 5% percenage points for every 1000'. I would like some eye protection good for an elevation of around 8000' or less, since my winter trips are at a lower elevation than that, but could go close to that if going to Lassen Volcanic National Park. I'm going to AK in a little bit and I guess we may visit a glacier while there and I want something finally to give my eyes decent protection that I can use in the future. Does anyone know, or have a chart? If I knew what the elevation was where a maximum of 5% light transmission starts at and could figure downward, I could figure this out.

Also, I need something to fit over my small glasses, someone mentioned Cocoons, but I can't find any info on their light transmission.

Interesting question. I've never seen such a chart.

I prefer sub 10% transmission for any mountain travel. Most important: the glasses need 100% UV cutoff. While the sun is definitely more intense up there, it's only a true problem when traveling on snow, where you need to deal with reflection from below in addition to the direct sun. For that I like gradient tint lenses that are darker below and above, as well as more complete coverage (larger, wraparound lenses). Even better if they're also polarized (polarized and tinted lenses can be difficult to find, but some makers have them). That and a dark brimmed hat or cap and I'm good to go.

Info I have read, says a wrap around design gives better coverage and a better view to the sides, not sold on polarized lenses as it seems they don't give very good depth perception, where as a grey or brown works better. 100% UV protection is what I want also. I definitely need something, as the last couple years on snow camp trips, around my eyes I get pretty puffy the next day. Look funny, like I had allergies real bad. I may go with some Cocoons, I need to go in and see what they offer in light transmission soon, as my trip starts early August. I know Cocoons don't offer sub 10% light transmission.

Well, not that I'm very experienced in the details of this, but I'll try and contribute as far as suggestions go.

I've got a pair of Oakley M-Frames with polarized lenses(thank you Army) that I used a lot in Iraq as well as when I got back to Alaska and we did a lot of winter training. Now I'm not sure if these are considered " wrap arounds" but they cover a lot of space on the face. They did however work great in both enironments, Iraq with its ruthless, never ending sunlight and Alaska in the winter when it was sunny got pretty darn bright and snow blindness was almost instant once you walked outside.

As for polarized lenses depth perception thing, I don't know that I can believe that. But as I said, I'm not sure if M-Frames are considered wrap arounds which if they are not, might be why I didn't notice any affect on my depth perception.

But anyway, that's my own experience, whether it's applicable or not I guess is up to you, lol.

Since you mention Oakley, I have some A-Wires with Black Irridium lenses that are both pola and tinted, totalling 9% transmission (they need repair now, but hey...).

Anyway, they're the best high-altitude glasses I've ever had. They stay put on my face and provide very good coverage.

FWIW light reflecting from the snow and water and to an extent from haze is polarized, and polarized lenses definitely help cut glare and enhance details. But a solely polarized lens does not provide a 90% block, which is why it should also be tinted, otherwise transmission can be as high as 35%.

Cheers,

I have no idea as to the transmission factor, but I have an old pair of Bolle glacier glasses with the leather side panels. They are super dark and work great in the snow or even at the beach.

I also wear a pair of goggles over my prescription sunglasses when I ski. I can swap out the lenses depending on the weather. I have yellow and dark gray lenses. The combo works well.

Make sure you wear something, though. You can get "snowburned" really quickly at altitude and it will fry your eyes for sure.

I never heard of light transmission either until I started checking out glacier glasses. Pretty important at higher elevations and on snow. Just because the lenses are dark, does not mean they are protecting the eyes, as that will allow the pupil? to open up and allow more damage. Lenses need to stop UV, IR and a sufficient amount of light also to protect eyes from damage. So much to digest! Arrgh! Let me out of here! Ahhhh!!!

I think you really have 2 questions to answer. The first is about the level of light that will damage your eyesight, and the second is about how dark is comfortable for you. the second question has a different answer for each person, as there is definitely a difference in light sensitivity from one person to the next. I, for instance, like very dark lenses. I'm the first guy to put on shades while others are doing fine without. I have a pair of Julbo Colorado glacier glasses, 5% transmission, and I often with they were darker. I use them year round, with the side shields for backcountry skiing, and without for backpacking in the summer. At 12,000 feet in early May on the snow, I wish they were darker. In August, on the dirt and granite, they are about right, and I use them at elevations down to about 6000 feet just fine. Your eyes my be more or less sensitive than mine, so your needs may vary. I tried some photocromic Julbos. which adjusted from something like 7 to 3 or 4%, but they did not fit me as well. I can defintely recommend the Colorados as a good value, only about $50 for a quality pair of glasses. I would suggest that any pair of glasses for which you can't find out the light transmission should be ruled out right away. Don't take any chances with your eyes. Better to get a pair of glasses that may turn out too dark for you than the other way around.