Color Vision (Part I) [20th July, 2021]

Color Vision

We tried to explore the concept of how we perceive different colors using our eyes and brain using the Phet simulation.


  1. What are photons?
  2. How we perceive the light fallen on our eye?
  3. How filter works?
  4. What light one will see through a yellow filter in a room where there is a bulb of red light?
  5. What is a monochromator and monochromatic light?
  6. How to construct white light using red, blue and green lights?
  7. What are primary and secondary colors?
  8. How to construct different colors using the primary colors?
  9. Share your thoughts, questions and comments regarding the simulation and your experience during exploring the simulation.

We welcome all kind of suggestions and feedback if this was useful and how can be collectively make it better.



Collaborators in video resource creation: Ravi Sinha, Smruti, Swarnava Mitra


PhET Interactive Simulations
University of Colorado Boulder


Here are interesting articles about “How do we see colours?”

The mechanism which helps us see the colours is pretty interesting. The article discusses what happens when light falls on an object (for example, on a ripe red apple). White light comprises waves of different wavelengths. The receptors in our eyes are sensitive to a certain range of wavelength ~ 380-750 nm.

Gringer, Public domain, via Wikimedia Commons

These light sensitive receptors (photoreceptors) are of two types - rods and cones. Rod cells get activated when light is dim (in darkness). Cones are the ones which get activated in bright light. Cones can be again classified into three types based on the range of wavelengths of light they are sensitive to - small wavelength(S-cone), medium(M-cone) and larger ones (L-cone).

BenRG, Public domain, via Wikimedia Commons

How do you perceive the apple as red? When white light falls on the apple, there are certain pigments in the skin of the ripe apple, which absorbs light in shorter wavelength range. The longer ones then get reflected and reach our eyes. This activates a larger proportion of cones cells of L-type as compared to S & M type cones. This signal is then taken by the optic nerve to the visual cortex of the brain where it gets interpreted as “red” by us.

In one eye, the number of rods cells(110 million) are ~18 times that of cone cells (6 million). Also, cones are located in the central region and rods are at the periphery on retinas.

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