There are two factors you must always keep in mind if you want to choose a pair of good running sunglasses. First of all, you must choose sunglasses lenses that can protect the eyes from any harmful rays, and shield your eyes from wind, sands, insects and other particles in the air. So, polarized lenses are recommended. Second, choosing eyeglasses frames made of strong and light weight materials so as to hold the lenses well and give you comfortable wearing.
A good pair of running sunglasses should have 100% UV protection to prevent all UVA and UVB rays damaging eyes. The color of the lens should depend on the weather condition. If you often run on sunny days, dark-tinted lenses like green and gray are best for you. If you go running on overcast days, brown-tinted lenses will be a better choice for you. CLear lens is also good for running on an overcast windy day. Anyway, make sure the running sunglasses are comfortable to wear.