As light passes through a spectacle lens, a percentage of it is reflected back from the surface of the lens, rather than being passed through the lens. Light can also be reflected off the back surface of lenses, towards your eyes, especially in situations where you are under overhead fluorescent lighting, or when driving at night with other car’s headlights around you. These reflections cause glare, which is uncomfortable, and also reduce the contrast of what you are looking at, making objects less easy to see.