A lens has a concave shape or a convex shape in either vertical cross
section or transverse cross section. Thereby light passing through the
lens is largely refracted and the interior is harder to be seen even if a
prism is not formed. As a result, there is no need to give a finish more
than optical performance required for reflection to the front surface of
the reflecting surface of a reflector, which is for the purpose of
enhancement of its appearance, and thereby the machining work is simpler
than the conventional way. Further, since the lens has a flat shape in
either vertical cross section or transverse cross section, the lens is
easily polished when it is made of glass, which is excellent in
manufacture of the lens.
