It depends on the sunglasses quality. You need a special facilities to filter the dangerous lights from the sun, which are certified for visual use. I mean, they can block the sun and protect your eyes, by a special coating that locks UV light. But you may get a pair of sunglasses without ability to protect your eyes because there is a relatively poor law system to enforce the quality of the sunglasses on the market, even if it costs you a lot of money. Further, your may suffer gradually retinal burns if the sunglasses fail to filter the invisible infra-red or ultra-violet radiation with dangerous amount. Well, the high quality eyeglasses products will reduce the sunlight to a comfortable level and the heat so that you eyes feel better in intensive lights.