In his experimental investigation on the production of electromagnetic
waves by means of a spark discharge, Hertz observed that high voltage
sparks across the detector loop were enhanced when the emitter plate
was illuminated by ultraviolet light from an arc lamp Light shining on the metal surface somehow facilitated the escape of
free, charged particles which we now know as electrons When light falls
on a metal surface, some electrons near the surface absorb enough energy
from the incident radiation to overcome the attraction of the positive ions
in the material of the surface After gaining sufficient energy from the
incident light, the electrons escape from the surface of the metal into the
surrounding space