Prism is used as a mirror to deviate light through 90 degree,
and also as a retroreflector to deflect light throgh 180
degree by total internal reflection.
90 degree deflection occurs at the
hyotenuse face.The image is erected and reversed.
degree deflection uses with hypotenuse as the entrance and
exit face.The mail application of it is used as a retroreflector
provided that the plane of incident beam includes the vertex.