Disagreeing About Yellow (prototype)

Adjust the color of one light to match the color of another.

Compare yellow finished


Green LED
Ultra-bright yellow LED
3 x 500 ohm potentiometers
1 50 ohm resistor
2 500 ohm resistors
1 battery holder for 4 x AA batteries
1 connector (9V battery type) to connect to battery holder
1 6 inch (15 cm) square pieces of wood
2 bare copper wires 12 gauge or larger 7 inches long
two ping pong balls
two film cans

Tools: wire cutter, wire stripper,needle nose pliers, hot melt glue gun,a nail file


Wiring for compare yellow

Hot melt glue the battery holder to the wood base.

Hot melt glue the 3 potentiometers to the base.

Bend the ends of the two wires around the edges of the base and hot melt glue them in place. These will be the bus bars for power and ground.

File flat the ends of the LEDs

Solder the 50 ohm resistor to the longer leg of the yellow LED

solder 500 ohm resistors to the longer legs of the red and green LEDs

Use short pieces of wire to connect the short lead of each LED to the ground bus.

Solder the 9 volt connector red lead to the bus bar that will be positive and the black lead to the ground bus bar.

Use short pieces of wire to connect the center of the three terminals on the potentiometer to the resistor on each LED.

Use short pieces of wire to connect one of the remaining terminals on each potentiometer to the positive bus.

Hot melt glue the yellow LED to a ping-pong ball

Hot melt glue the red and green LEDs side by side to the other ping pong ball.

Hot melt glue the ping pong balls to the film cans and hot melt glue the film cans to the base.


To Do and Notice

This works better in a dimly lit room.

Snap the battery connector onto the battery holder. The lights should come one.

Adjust the potentiometers until the colors of the two lights are as close to being the same as possible.

Ask another person to make the adjustment.

Do you agree on each others choices?

What's Going On?

The sensitivity of the red cone to different wavelengths of light is different in many people.

This means that two different people can look at the same colors and see different colors.

We can show this by creating yellow light in two different ways: create light of one wavelength that excites both the red and the green cones to perceive a yellow-ish color, and create two different wavelengths of light one that excites red cones and one that excites green cones and adjust the brightness to make light that is perceived to be yellow-ish.