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f-alpha.net » Electronics » Optoelectronics » Light-Emitting Diode (LED) » Let's go... » Experiment 8 - Colored LEDs

Experiment 8 - Other Colored LEDs

To investigate this, use the yellow, green and blue LED and measure the forward voltage.

You will be surprised how great the differences are. Typical values for the forward voltage are...

  • red: 2.0 Volt
  • yellow: 2.1 Volt
  • green: 2.2 Volt
  • blue: 3.0 Volt

Circuit diagram voltage measurement of the colored LEDs.

Circuit measuring the forward voltage of a yellow LED. (Enlarge)

Circuit measuring the forward voltage of a green LED. (Enlarge)

Circuit measuring the forward voltage of a blue LED. (Enlarge)

Your actual measured values ​​may differ greatly from this. The forward voltage drop is determined by the used semiconductor material and this information you find only from data sheets.

                                                                                                                                                                                                                                                                                                                                                                                                                                                  
ColorULEDMaterials
infrared < 1.9 VGaAs, AlGaAs
red 1,6 - 2.0 VAlGaAs, GaAsP, AlGaInP, GaP
yellow 2.1 - 2.2 VGaAsP, AlGaInP, GaP
green 1.9 - 4.0 VInGaN, GaN, GaP, AlGaInP, AlGaP
blue 2.5 - 3.7 VZnSe, InGaN, SiC

Forward voltages and materials used by common LEDs (Source: Wikipedia).

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