How do unpolarized sunglasses reduce brightness?

[dan1]

Hi everyone!

I've been reading up on light and transmission, absorption and reflection and I was wondering how unpolarized sunglasses are able to reduce brightness. I tried Google-ing this but all I found was information about polarized sunglasses and how they reduce glare and work as UV protection but I have a fairly solid understanding of that. How do basic sunglasses work? Do they reflect some frequencies of light but let others through? If so, which ones?

Thanks for all your help!

 

[mathman]

Ordinary sunglasses absorb some of the light. That's why they look dark.

 

[dan1]

If you don't mind me asking, how are they able to do this and which frequencies of light do the absorb?

 

[fluidistic]

If you don't mind me asking, how are they able to do this and which frequencies of light do the absorb?

I typed in google "sunglasses materials", the first link was http://www.madehow.com/Volume-3/Sunglasses.html.
There you can read

Soluble organic dyes and metallic oxide pigments are added to the lens material to absorb or reflect light of certain frequencies.

The frequencies absorbed depend on the material composing the glass. If you really want to know why some material are transparent and others not, I suggest to take a look at http://www.quora.com/Why-are-some-materials-transparent-and-others-not and http://en.wikipedia.org/wiki/Transparency_and_translucency.