Originally Posted by
gsa103
Plastic is inherently UV absorbing (even clear plastic). As a result almost any pair of sunglasses provides decent UV protection. You would actually have to work fairly hard to find glasses that didn't block UV. The only way sunglasses wouldn't block UV is if they were really really thin and obviously flimsy.
» Blog Archive » UV Measurement of Sunglasses using a Back-thinned CCD Spectrometer
Basically, every single pair they tested blocked >99% of UV (OD>2 for wavelength <400 nm).
Cheap sunglasses can suck for all sorts of reasons, but UV protection is likely the least important reason.
Consumer Reports also came to the same conclusion in their testing, a few years back.
The bigger problem with cheap glasses (in addition to lack of durability) is lens distortion.