Specular reflection is the
mirror-like
reflection of
light (or of other kinds of
wave) from a surface, in which light from a single incoming direction (a
ray) is reflected into a single outgoing direction. Such behavior is described by the
law of reflection, which states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle with respect to the
surface normal, thus
the angle of incidence equals the angle of reflection (
in the figure), and that the incident, normal, and reflected directions are
coplanar. This behavior was first discovered through careful observation and measurement by
Hero of Alexandria (
AD c. 10–70).