What color an LED emits depends on the energy level of the charge transition from the non-conduction band to the conduction band. Depending on the basic material (Si, GaAs, GaN etc.) and doping, as well as the internal resistance every LED has a typical operating voltage (voltage = potential = energy difference). Although this is modified by the design (internal resistance, etc.), in the final analysis it is determined by the discrete energy level of the charge transition between non-conduction and conduction band.

Information and ideas:
The abstract principle of the quantization of energy in the form of photons is demonstrated clearly in an extremely simple experiment with four LEDs and a power supply unit. Red LEDs light up at a voltage from about 1.5 volts, yellow from about 1.9 volts, green from about 2.3 volts and blue from about 3.3 volts.
Instructions for building a variable LED color mixer can be found in the experimentation instructions “Experiments – energy quantization with LEDs" on the media portal of the Siemens Stiftung.

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Physics; Technology

Grade 5 to 6; Grade 7 to 9; Grade 10 to 13

Middle/high school

Color Theory; Light; Semiconductor; Wave (physics); Color formation; Electroluminescence; Light generation; Light-emitting diode (LED); Wave (physics)

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