The energy of a photon is related to its frequency by the equation E = hf, where h is Planck’s constant. By determining the potential required to excite an LED to emit light, you can estimate the energy of the photons emitted. Using a spectrometer, you can measure the peak wavelength of the emitted light; from this, the frequency can be calculated. Performing this analysis for a number of LEDs will enable you to obtain a reasonable approximation of the value of Planck’s constant.


In this experiment, you will

  • Collect and analyze current vs. potential data to estimate the energy required to excite a number of LEDs.
  • Use a spectrometer to determine the wavelength of the peak output of each LED.
  • Determine a value for Planck’s constant from an analysis of the energy and frequency of the light emitted by a number of LEDs.