Blended Lights

Eli Whitney Museum

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For School Groups


When the primary colors of light, red, green, and blue are mixed, white light is produced. By looking at the shadows cast when an object blocks one or more of these color components, you can observe both the additive and subtractive processes of color mixing. Instead of subtracting light via an absorbing pigment, the object's shadow "removes" the component color from the "white" light. For example, the yellow shadow is the result of blocking the blue led and only allowing red and green to mix. Similarly, yellow pigment absorbs blue light and reflects red and green. The addition of red and green light makes yellow. The bluish-green shadow - CYAN - is the result of blocking the red light.

Where the cyan and yellow shadow overlaps appears to be green. Why? This small shadow is where both red and blue are blocked. Likewise, when we mix cyan and yellow pigment cyan absorbs red and yellow absorbs blue. The only thing left to be reflected is green. Cyan pigment and yellow pigment both reflect green, so that's what we see. (In white light)

We are accustomed to teaching with a model in front of a child, but these instructions should make it so that anyone can build one without our presence. We urge that parents and teachers be there to guide – but to allow the child to try to let the materials (and a picture of the final product) guide them. A wrong direction is always un-doable until you've glued something.

The Parts.

Step 1. Place the three small 1/4" dowels in the holes in the front. Place the 3/16" dowel in the hole near the opposite end.

Step 2. The three wheels will be stored on those three small dowels. Find the center of the screen and slide the center opening down over the 3/16" dowel. Remove the 1/8" plywood pieces from the 'matrix'.

Step 3. Put the small round disc onto the 'finger' of the plywood strip and slide the disc/strip assembly into the slots on the wheels.

Step 4. The LED ultrabright keychain lights will slip onto the vertical 'fingers' in the wheels. When they are lit, they should be moved backward off the storage base so that you can play around with the distance of each of them. When all three overlap (R + G + B) they will create a white light in the center. If you put an object in front of them, the shadows they cast will be the 'sum' or 'difference' of two of the others. Try using different objects in front of the lights to see what happens. Punch holes in a piece of paper and see what color shadows you get.

Or, try putting a 'clear gem' in front to see what the facets do to the light. Pretty neat.

Step 4

Step 1

Step 2

Step 3

Step 5

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