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Article: Reflection (physics)

Reflection (physics)

Reflection of light

  • Reflection of light can be either specular (mirror-like) or diffuse (retaining energy but losing the image).
  • Specular reflection occurs at the surface of a mirror or transparent media like water or glass.
  • The angle of incidence equals the angle of reflection, according to the law of reflection.
  • Reflection can occur when light travels from a medium with one refractive index to a medium with a different refractive index.
  • Total internal reflection occurs when the angle of incidence is greater than the critical angle, and it is used in applications like X-ray telescopes.

Laws of reflection

  • Specular reflection occurs when the reflecting surface is very smooth.
  • The incident ray, reflected ray, and normal to the reflection surface lie in the same plane.
  • The angle of incidence is equal to the angle of reflection.
  • The reflected ray and the incident ray are on opposite sides of the normal.
  • These laws can be derived from the Fresnel equations.

Diffuse reflection

  • Diffuse reflection occurs when light strikes the surface of a non-metallic material and bounces off in all directions.
  • It is caused by multiple reflections by microscopic irregularities inside the material and on its surface.
  • The exact form of diffuse reflection depends on the structure of the material.
  • Lambertian reflectance is a common model for diffuse reflection, where light is reflected with equal luminance or radiance in all directions.
  • Diffuse reflection is the primary mechanism of physical observation for most objects we see.


  • Retroreflection is a phenomenon where light is returned in the direction from which it came.
  • Some surfaces exhibit retroreflection, such as those with curved droplets or corner reflectors.
  • Retroreflection can be seen when flying over clouds or with dew on grass.
  • Animals like cats and dogs have retinas that act as retroreflectors, improving their night vision.
  • Retroreflective surfaces can be created using mirrors or by depositing refractive spheres or pyramid-like structures.

Light-matter interaction

  • In classical electrodynamics, light is considered as an electromagnetic wave described by Maxwell's equations.
  • Light waves induce small oscillations of polarization in atoms or electrons, causing each particle to radiate a small secondary wave.
  • The combination of these secondary waves gives rise to specular reflection and refraction.
  • In dielectrics like glass, the electric field of light acts on electrons, generating forward and backward radiation that contributes to refraction and reflection.
  • In metals, free electrons oscillate with incident light, resulting in cancellation of forward radiation and reflection of backward radiation.

Multiple reflections (subtopic)

  • Light reflects off a mirror, creating one image.
  • Two mirrors placed face to face produce an infinite number of images along a straight line.
  • Multiple images between two mirrors at an angle lie over a circle.
  • Four mirrors placed face to face create an infinite number of images in a plane.
  • Multiple images between four mirrors forming a pyramid lie over a sphere.

Complex conjugate reflection

  • Phase conjugation causes light to bounce back in the opposite direction.
  • Wavefronts are reversed in complex conjugate reflection.
  • Conjugate reflectors can remove aberrations from a beam.
  • Looking into a complex conjugating mirror would appear black.
  • Only photons that left the pupil would reach the pupil in a complex conjugating mirror.

Other types of reflection

  • Neutron reflection
  • Beryllium and other materials reflect neutrons.
  • Neutron reflection is used in nuclear reactors and weapons.
  • Reflection of neutrons off atoms helps determine internal structure in science.
  • Sound reflection
  • Longitudinal sound waves reflect in a coherent manner on a flat surface.
  • Reflection of sound depends on the texture and structure of the surface.
  • Porous materials absorb some sound energy.
  • Rough surfaces scatter sound energy in many directions.
  • Sound reflection affects the acoustic space and is important in architectural acoustics.
  • Seismic reflection
  • Seismic waves produced by earthquakes are reflected by layers within the Earth.
  • Reflection seismology uses shallow reflections to study the Earth's crust and prospect for petroleum and gas deposits.
  • Deep reflections of earthquake waves help determine the layered structure of the Earth.
  • Seismic reflection has contributed to understanding the Earth's composition.
  • Reflection seismology is used in oil and gas exploration.

Reflection (physics) Data Sources

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