Definition of a Prism

• A prism is a transparent polyhedron (many-sided) that has two non-parallel faces and is used to either deviate or disperse a beam of light.
  
  

Total Reflection Prisms

• The most common type of prism is a total reflection prism, which is made of glass with two 45-degree angles and a 90-degree angle to the three faces of the crystal. This is the classic prism used to introduce students to the physics of light.
  
  

Lummer-Brodhun Cube Prisms

• The Lummer-Brodhun cube prism actually combines two types of crystals to develop the desired properties. One crystal is a total reflection prism, and the second has the face determined by the 45-degree angles ground to a curve. This allows physicists to do photometric studies when comparing the illumination of two surfaces.
  
  

Polarizing Prisms

• Passing a beam of light through a calcite crystal cut to form a prism results in polarized light, which is light that has been broken (refracted) into separate frequencies and emerges from the crystal in parallel. Polarizing prisms are used in optical microscopy and for spectroscopic analysis.
  
  

Prisms on the Moon

• Physicists studying the movements of spatial bodies make use of prisms by taking advantage of their light reflecting properties. In the 1970s, astronauts placed a prismatic construct on the surface of the moon. These prisms reflect light from a laser that is been beamed from the Earth to the moon to calculate the rate of movement of the moon away from the Earth.
  
  

Practical Application

• Ophthalmologists make use of two thin prisms of equal power that can be rotated to measure binocular accommodation. This allows an ophthalmologist to diagnose eye diseases.