Electrons bound to a plate by their electric interaction require a high enough incident light frequency to be released. This is called the Photoelectric Effect and this lab will allow us to explore this phenomenon

Planck's Constant

Appling a large enough voltage difference across a diode will excite the electrons across the energy gap and into the conduction band.  In the subsequent return to the valence band a photon will be released.  With a great enough voltage current will flow through the diode.  This discrete "turning on" effect will be observed.