  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.
