Rather than the energy continuity considered in classic physics, the energy level of a photon or an electron, viewed from quantum theory, exhibits an integer multiple of hf (here h is planks constant and symbol
of f indicates the frequency of light wave). That means a light is emitted from or absorbed by an electron and the energy, hf, will be quantized. While laser light is irradiated to a light-emitting diode, the induced current will be further retarded due to weaker forward voltage unable to overcome the energy barrier, i.e., most electrons are still constrained in depletion layer. However, a current of fast growth starts being induced if potential supplied V₀ is just adequate to break through the barrier. Thus planck’s constant h might be determined from the equivalence of energy emitted from laser diode, hf, and power absorption of photon e ( V-V₀).