If red and green cones in our eyes are tiggered simultaneously then our brain makes us see yellow color.

But if two objects which have red and green colors respectively are placed infront of us then in that case also red and green both wavelenghts of light are entering our eyes simultaneously. And red and green cones are being triggered simultaneously.

Then why we see red and green colors seperately and simultaneously instead of seeing yellow ?

  • $\begingroup$ You are lucky you see red and green separately, I am red-green colour blind :( $\endgroup$
    – Courage
    Jan 29, 2016 at 6:42
  • 3
    $\begingroup$ Because eyes can tell what angle things are coming from? If you had a red and green light coming from exactly the same place, it would just look yellow. $\endgroup$
    – knzhou
    Jan 29, 2016 at 6:50
  • $\begingroup$ I think these videos are amazing about color vision. I believe if one watches all the way up to part 9, this question will be easy. Here is part 1. youtube.com/watch?v=iDsrzKDB_tA $\endgroup$ Jan 29, 2016 at 9:10

1 Answer 1


If the 2 objects are at different locations, then the green light is hitting different group of cones in your eye than the red light. You should thank to the lens in your eye which is sending the light rays to different areas on your retina, depending on the direction from which the light is coming. Without the lens, all light would hit all cones at the same time and you would "see" only a homogenous fog. Red and green would mix to yellow.


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