Reflected sunlight (from the water, for example) is particularly dangerous. There is also evidence that exposure to UV light can contribute to the development of eye diseases that commonly occur as we age, such as cataract and macular degeneration.
Visible light is the part of the sun's energy that you can see. It is made up of a spectrum of colors: red, orange, yellow, green, blue, and violet. The eye is not equally sensitive to all of these colors. It is most sensitive to yellows and greens which it can see the best. The eye is less sensitive to reds and blues. Different Ultraviolet Rays Ultraviolet rays have shorter wavelengths and more energy than visible light rays. They can have a harmful effect on the eyes immediately or cumulatively from regular exposure over a number of years. The industry has set standards for how much UV may be transmitted (passed) by types of sunglasses. Ultraviolet (UV) rays are strongest at high altitudes, low latitudes, and in open or reflective environments (like sand, snow, or water). They are also strongest at midday. Scientists divide UV rays into three bands according to wavelength: UVA, UVB, and UVC.
UVA rays have been shown to penetrate the under layers of the skin, causing damage and contributing to the skin's aging and cataracts. Therefore, it is certainly wise to require protection from them in sunglasses.
UVB rays, the sunburn rays, are the ones that cause the most concern. They can cause keratitis, which is similar to sunburn on the eye, and also have been linked to the development of cataracts.
UVC rays are the shortest, the most energetic, and may be the most harmful. Fortunately, they are blocked in the upper atmosphere and never reach the earth. If sunglasses protect against UVB, we can assume they protect against any possible exposure to UVC.