Angle of incidence

The angle of incidence measures the angle at which incoming light strikes a surface.

  • When light is travelling towards something it is said to be incident to that surface or object.
  • The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • Expressed more formally, in optics, the normal is a geometric construct, a line drawn perpendicular to the interface between two media at the point of contact. This conceptually defined reference line is crucial for characterizing various light-matter interactions, such as reflection, refraction, and absorption.
  • Incident light may have travelled from the Sun or a man-made source or may have already been reflected off another surface such as a mirror.
  • When incident light strikes a surface or object it may undergo absorption, reflection, refraction, transmission or any combination of these optical effects.
About lines that are normal to one another
  • If one line is normal to another, then it is at right angles.
  • In geometry, a normal (or the normal) refers to a line drawn perpendicular to and intersecting another line, plane or surface.
  • In the field of optics, the normal is a line drawn on a ray-tracing diagram perpendicular to (at 900 to), the boundary between two media.
  • If the boundary between two media is curved then the normal is drawn at a tangent to the boundary.
Related diagrams

Each of the diagrams below can be viewed on its own page with a full explanation.

References
  • The angle of incidence measures the angle at which incoming light strikes a surface.
  • The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
  • See this diagram for an explanation: Reflection of a ray of light
  • In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (900), the boundary between two media.
  • If the boundary between the media is curved, then the normal is drawn at a tangent to the boundary.