Planck’s Constant relates the energy of light photons to their frequency. It also shows up in de Broglie’s relation for the wavelength of matter waves and Schrödinger’s Equation. Thus, the number is of fundamental importance in 20th Century physics. A common device, the light emitting diode or LED, could be designed only because some engineers understood quantum science. Thus, knowledge of the value of Planck’s constant is “hidden” in the LED. This short tutorial will show you how you can determine a value for Planck’s Constant by using LEDs.