Planck s constant apparatus rvfm 52 2639 this apparatus is designed to determine the approximate value of planck s constant using a range of leds of known wavelength to allow the electron photon energy to be calculated the apparatus includes 7 leds covering the light range from deep blue at 470nm to near ir at 940nm mounted on a box with 4mm sockets for attachment to a voltmeter and ammeter for voltage and current measurements by monitoring the voltage at which each led just begins to e