Automotive rearview mirrors are classified by their mounting location into exterior mirrors, downward-facing mirrors, and interior mirrors. In terms of function, exterior mirrors show the area to the rear and side of the vehicle; downward-facing mirrors show the area in front of and below the vehicle; and interior mirrors show the area directly behind the vehicle as well as the vehicle's interior. Differences in function lead to differences in mirror surface structure. There are two main types of mirror surfaces: flat mirrors and convex mirrors. Flat mirrors-as the name implies-have a flat surface (technically described as having a surface radius of curvature of infinity). Like standard household mirrors, they produce an image that matches the size of the object as seen by the naked eye; these are commonly used as interior rearview mirrors.
The other type is the convex mirror, which has a spherical surface with a specific radius of curvature. These mirrors produce images that appear smaller than the actual objects but offer a wider field of view-functioning much like a camera's wide-angle lens. Convex mirrors are commonly used for exterior and downward-facing mirrors. Sedans and other light passenger vehicles are typically equipped with exterior and interior mirrors, whereas large commercial vehicles (such as buses and heavy trucks) are generally equipped with exterior, downward-facing, and interior mirrors.