Reflection

Reflection, bouncing back of energy waves (e.g., light radiation, sound or water waves) from a surface. If the surface is smooth, “regular” reflection takes place, the incident and reflected wave paths lying in the same plane as, and at opposed equal angles to, the normal (a line perpendicular to the surface) at the point of reflection. Rough surfaces reflect waves irregularly, so an optically rough surface appears matt or dull, whereas an optically smooth surface looks shiny. Reflected sound waves are known as echoes.