Quantum mechanical constraints on the measurement of the density of the electromagnetic energy

It is considered constraints imposed by the quantum mechanics on the measurement of the density of the electromagnetic energy. First, the energy of the electromagnetic wave and the volume (time) are bound with the Heisenberg uncertainty principle. It reduces from double to ordinary the relativistic effect for the density of the electromagnetic energy. Second, the frequency of photons and the number of photons are bound with the Heisenberg uncertainty principle. Then relativistic effects for the frequency of photons and for the number of photons are incompatible. The energy density of the electromagnetic wave is given by