Your senses can be tricked.  You might think you’re looking at a large, yellow, bird-like object, but that is only true if the right color of light is shining on it.

 

You’ll learn about the electromagnetic spectrum in the last week of class.  Visible light is a very small part of the electromagnetic spectrum even though it contains all the frequencies of light you can see.  Most light bulbs are clear or white and give off white light, but you can buy colored light bulbs or gels you can put over lights to change this.  White light is actually all the colors of light, the combination of multiple frequencies, so that clear light bulb is actually giving off every color of light.  A colored light bulb will only let one frequency of light through.

 

So why does that large, yellow, bird-like object appear yellow?  Pigment works by absorbing certain frequencies and reflecting others.  The object appears yellow under white light because the frequencies that were reflected combine into yellow light.  The object absorbs the complementary frequency, blue light.  The truth about this object is not that it is yellow, but that it absorbs the blue frequency of light.  The object will not always appear yellow, but it will always absorb the blue frequency.

 

Imagine this yellow object in a pure white room with white light shining in the room.  Now, cover all the light bulbs with cyan gels.  Cyan is the color combination of green and blue light.  The object absorbs the blue light and reflects the green light.  The room will look cyan and the object will be green instead of yellow.

 

Why does this matter?  If you are lighting a stage, the color of the lights can dramatically change what the audience sees and the mood of the production.  If you are animating a world, you need to know how to realistically create it.  If you are solving a crime that took place in the middle of the night, you need to know if the streetlight affected the witness’s description of the car.  If you want to amaze your friends, you can change their clothes without removing them.

 

So the next time you see a large, yellow, bird-like object remember it’s only yellow because of the lights.

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