Different Colors of LEDs

Another experiment to corroborate this model for LEDs is the threshold voltages, or the voltage at which LEDs turn on, for different colors of LEDs.

First, obtain LEDs and the LED apparatus consisting of a battery, switch, and sockets for voltmeter inputs. Attach an LED to the assembly as well as a voltmeter, then, while turning the potentiometer, see at what voltage LEDs of different colors come on and compare your results with others. Finally, try it with the white LED. What do you observe?

Threshold voltage of   color LED:           V
Threshold voltage of   color LED:           V
Threshold voltage of   color LED:           V
Threshold voltage of   color LED:           V
Threshold voltage of   color LED:           V
Threshold voltage of   white color LED: V

To use LEDs as normal light sources we would like to have LEDs that produce white light. Such LEDs have been recetly produced. Turn one on and look at the light that is emitted from them. Use what you know about the way LEDs produce light to come up with some models which describe how one might produce white light in an LED. Try to create at least two different models.

Compare your model with others in the class. Together pick a few that you would like to test. Then, outline experiments that could test each of the models.