Colored Shadow Light

Colored Shadows Not all shadows are black. When lights of different colors shine on the same spot on a white surface, the light reflecting from that spot to your eyes is called an additive mixture because it is the sum of all the light. We can learn about human color perception by using colored lights to make additive color mixtures.

Additive color combination happens when you overlap two or several beams of lights of different colors, a principle that is used in most electronic visual displays. Subtractive combination of colors happens when you shine a light through colored filters, which each will subtract (or absorb) some wavelengths of the original light. The Colored Shadows Interactive is shown in the iFrame below.

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With just a single colored light, you'll find that colored light does indeed produce a "black" shadow (the absence of light), just like your intuition suggests. However, in the linked example, they don't just have one light, they have three of different colors. In that case, in the shadow from one light you still have two colored lights lighting up the background.

Those two colored lights mix. When the three coloured light bulbs all shine on the same surface, we see all the wavelengths from red through to purple, which we perceive as white. With these three coloured lights you can make shadows of seven different colours: blue, red, green, black, cyan (blue-green), magenta (pink), and yellow.

As each flashlight is shining from a different angle some light can still reach the wall, creating coloured shadows. Try pointing a rod or stick in the middle of the focused 3 lights you should see a magenta, cyan and yellow colour which are the secondary colours formed from the red, blue and green primary colours of light. To his amazement, instead of the background becoming filled with all 3 colors, it actually created a white background, as we normally see it.

However, more impressively, the shadows were not black, but multi. Using three colored light bulbs, it is possible to not only create colored shadows, but six different colored shadows from a single object. What colors do you see? Use colorful shadows to explore how your eyes detect a rainbow of hues.

You can even create your own blends, painting with light! Colored Shadows So your physics teacher is standing in front of the white screen in the front of the room. The room lights are off and you're in charge of the three colored spotlights.

With a flip of a switch, you can shine any combination of red, green and blue light on the teacher.