(This is related to, but different from, this question.)
Cost is never a guarantee of quality. But for some products, low cost is a guarantee of lower quality. For example, while not all $300 speakers necessarily sound good, no $30 speaker can sound as good as a good $300 speaker, due to physical limitations of what can be manufactured at that price point.
Compare that to, say, handbags, where price is primarily a matter of branding, but an inexpensive model might function just as well as an expensive one.
So: Are sunglasses like speakers, or like handbags? What features might I find in $300 sunglasses that could never be available in $30 sunglasses?
I know several people who swear that they hated wearing sunglasses for years until they got a $200-$300 pair and looking through them was a revolutionary experience, and they've worn sunglasses daily ever since. But, knowing how powerful branding can be, I'm skeptical.
This site claims that there are four factors that affect sunglass quality:
- Sunglasses provide protection from ultraviolet rays in sunlight.
- Sunglasses provide protection from intense light.
- Sunglasses provide protection from glare. (i.e. polarization.)
- Sunglasses eliminate specific frequencies of light.
I'd add a fifth criterion - Sunglasses might be more useful if they block more light from certain angles, i.e. sunglasses with gradients, since the brightest light is generally coming from above.
However, the linked article suggests that expensive sunglasses do those things better than cheap ones, which doesn't fit with my experience.
Zenni Optical, for example, sells sunglasses with prescription lenses starting at $15 with UV blocking and a brown gradient tint, one of the most popular styles for expensive sunglasses. (They charge $33 for polarized lenses, so that's still not expensive. And, I'd add that many much more sunglasses forgo polarization, so it's not necessary for quality lenses, and it has its disadvantages too.)
The only reason I can think that expensive lenses might give better quality are in the specific absorption spectrum of the tint. The ideal lenses for most people would block as much as possible of the specific blue frequencies that come from the sky, which is usually the brightest part of any outdoor scene, and would probably block as little as possible of flesh tones, so you can still see faces clearly. This is why brown lenses are so popular in high-end sunglasses - they do exactly that.
It is entirely possible, in theory, that expensive lenses could use rarer pigments that, while they look at a glance like the same color, block different specific frequencies. However, I haven't found a single claim that this is true - even from companies that sell expensive sunglasses!
So, is there anything to this claim?