Gradient sunglass lenses are tinted from the top, all the way down. Hence, the top portion of the lens is the darkest. These lenses are great for driving because they will shield your eyes from overhead sunlight and allow more light.Double gradient sunglass lenses are where the top and bottom portions are dark, and the mid-section is light. These sunglasses are perfect when you want to shield your eyes from reflective surfaces but don't want them to be too dark.