Green Shadows


Activity:  Is it really green?

Kind: individual or with a friend, can be a child

Duration: 5-10 minutes


  1. Indoors, in dim light, at a table or on the floor.  You need two lights, either table lamps or flashlights and a way to hold everything in position.


  1. 1)In your course package you will find a pinkish red plastic folder.  Take out the stickers that were packaged inside for protection, you will need them later for another activity.  For now you need only the red plastic. (The colour of this plastic is not ideal, if you have red cellophane on hand that might be better. This was just the best I could find for you at the time - and it works OK, though not dramatically.)

  2. 2)set up your lights so both shine on a white surface from different angles.  I demonstrate one set up in my video, below.  The diagram might also be helpful.  If you’re using flashlights you’ll have invent some way to hold them, perhaps another person.

  3. 3)In a dim or dark room turn on the two lights and hold the red film in front of one of them while you move an object or your hand into the light so you get two shadows.  You can experiment till you get the right angles for lights and shadows to make this work.

  4. 4)what colour are the two shadows?  They won’t be nearly as marked as in the diagram, yet you should be able to see a dark brownish one and a greenish one.

  5. 5)Where does the green come from?  This is not a simple matter of mixing two coloured lights as you have one white light and one red one.  Think about it!

This YouTube video shows you a lovely demonstration of
how colour you perceive is also a matter of focus.

from el árbol del conocíemíento, Maturana and Varela, 1984 p. 9

further interest