To tell if a pair of sunglasses is UV protected, you've got twe ways:

1) If there is a tehnical UV tester sunglasses uv tester, it can easily tell if you have bought a sunglasses that is VU protected. The only problem is that we ordinary people don't have to own a professional machine at home, and it may cost you much money while you don't have to use it often at all. 

2) You can shine a blacklight flashlight on something that fluoresces. When you place the lens in front of the flashlight (in the middle of the object fluorescing and one of your sunglasses lenses), if it blocks the light, then your sunglasses has the UV protection coating!

What is a 'Blackligh Flashight'? It is a flashlight that gives ultraviolet itself! That means you can use that kind of flashlight like a sun with ultraviolet rays.

What kind of thing that fluoresces and you can get it with ease? Acutally most of cashes (for emample US dollars or Chinese yuans) have the fluorescent thing hidden in it and your naked eyes don't tell. When you put a ultraviolet flashlight over the cash, it fluoresces somewhere!

The last thing that you need to do, is to get such a cash, and turn on an ultraviolet flashlight and put it over the cash, when it fluoresces, put your sunglasses in the middle, then see what happended. If the cash stop fluorescing, then your sunglasses is UV protected!

uv protected sunglasses Here is an illustration, when a cash fluoresces (where there is tiny fluorescing number 100 occurs above a big printed number 100) under an ultraviolet flashlight, put a sunglasses that is NOT UV protedted in the middle, that tiny 100 is still there.

non uv protected sunglasses Replace that sunglasses with another UV protected one, that tiny 100 disappears!