  Using very simple arguments we show that the quantum effects of an
ultra-light particle as the Scalar Field Dark Matter $m_{SFDM}\sim10^{-22}$eV
cannot be neglected at classical scales. We show that the effective density of
this effect is constant in the space and for such a mass, it is of the order of
magnitude of the critical mass of the universe. Thus, we can interpret the
effective density of this quantum effect as the cosmological constant.
