  Plank's constant is a fundamental constant in Physical sciences and Millikan
received Noble prize for obtaining it experimentally in 1923. As the technology
of solid state electronic devices developed, an experiment was designed and
adapted to determine the Plank's constant using LED. Herrmann and Sch\"atzle
questioned the validity of this experiment on the basis of the diode equation
and their approach was further discussed by Morehouse. In this article, the
validity of this experiment is revisited.
