Sunlight is the primary source of UV light. Too much exposure to UV results in various long-term eye issues. People usually buy sunglasses as a preventive measure to these problems. As much as they may labeled to provide UV protection, most sunglasses do not. For the sunglasses that have reliable safety ratings, their UV protection wears off with time.
How can people tell if their sunglasses are 100% UV protected? This is a question that has troubled many minds. There exists no independent verification of the UV protection claims made by various brands. It is important to note that a higher price provides no guarantee of UV protection. I have tested numerous expensive sunglasses that have claimed to offer 100% UV protection only to bear witness to their shameless deception to the public. Surprisingly enough, I found some relatively cheap glasses, ranging from $8 to $25 offering effective UV protection.
Testing can be one with a simple trick that will require access to a UV flashlight. You can find an affordable UV flashlight online or borrow one. Once you have it, go with it into a darkroom together with the sunglasses and paper money or a credit card. Turn on the flashlight and beam it on the credit card or money. Various strange symbols that you do not usually see in ordinary light will become visible. They include a line on the paper money and letters on credit cards. These are watermarks that the government and banks use to identify counterfeits.
After confirming the appearance of the strange symbols, you can proceed with the testing of your sunglasses. Beam the UV light through one of the lenses and onto the credit card or money. If the symbols are still visible, your glasses are not 100% UV protected. This means the lens is letting the UV light through and as a result, the symbols become noticeable. However, if you cannot see the symbols, the sunglasses offer 100% UV protection. The lens is blocking the UV; hence, the symbols are no longer visible.
Sadly there is little regulation of sunglasses as labelling can be deceptive. Over the years, this test has led me to discover that many expensive sunglasses which are said to provide 100% UV protection do not. I would advise all buyers, if possible, to test their sunglasses at the store. If you have already bought them, return them immediately for a refund.