Anyone know about light transmission in sunglasses?

[Melchett]

What I mean is, does the quoted % of light transmission directly equate to the 'category' or 'protection index', e.g. cat 1 to 4?

The reason I ask is because im going climbing at altitude and need some cat 4 glasses. But, I have found glasses that are reportedly 'cat 4' but let through 10% of the light. Whereas others are cat 3 and let through 9% of the light. Whats the score here?

Cat 3, 9% transmission (see lens tints tab at bottom)
http://www.oakley.com/pd/4672/22505

Cat 4, 10% transmission
http://www.sports-sunglasses-eyewear.co.uk/prescri...

[Yoshiwaan]

I think many people are going to see that topic and think it's a physics question... I did.

[jshell]

It's possibly the difference between 'visible light transmission' v's 'uv light transmission'. The first one lets you see, the other one can damage your eyes. Not sure, but that could be the reason for the varying ratios.