Optics 101

What is a Prism?

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A prism is a transparent, geometric, optical object with a minimum of two polished plane faces inclined relative to each other, from which light is reflected or refracted. Prisms are made from transparent materials such as glass, plastic and fluorite.

They are used to redirect light at a designated angle. They have the capacity to reverse the direction of light by internal reflection.

Prisms are usually categorized based on the shapes of their bases. For example, there are triangular, rectangular, hexagonal prisms. Its design determines how light interacts with it. An ordinary triangular prism can separate white light into its constituent colors.

When light enters a right angle prism, it reflects off a single surface, thereby causing light to be redirected at 90°. Similarly, when light enters a wedge prism, it causes the light to deviate through refraction.

Prisms have to be manufactured with very strict tolerances and accuracies, and hence require a skilled optician to manually inspect and adjust the prism surfaces being created.


Different types of prisms include dispersive prisms, which are used to break up light into its constituent colors, reflective prisms, which are used to manipulate beams of light to flip them, invert them etc., beam-splitting prisms, which are used to split a beam of light into two separate beams, polarizing prisms, which split light into different components based on their varying polarizations and finally deflecting prisms, which are set at a fixed angle usually and deflects light according to it's specific angle.


There are various applications for prisms. They are made in many different forms and shapes to suit specific applications. Prisms are heavily used in optical applications such as microscopes, lenses, telescopes and laser diodes. Other examples include:

  • Interferometry
  • Pattern recognition
  • Rangefinders
  • Laser instrumentation
  • Beam steering
  • Tunable lasers
  • Forestry
  • Stereo microscopes
ABC Zoom - Refraction: why glass prisms bend and separate light

Refraction: why glass prisms bend and separate light.
Video sourced from YouTube -


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