  We study the constraint of the non-SUSY AdS conjecture on the
three-dimensional vacua obtained from the compactification of the Standard
Model coupled to Einstein gravity on a circle where the three-dimensional
components of the four-dimensional metric are general functions of both
non-compact and compact coordinates. We find from studying the wavefunction
profile of the three-dimensional metric in the compactified dimension that the
radius of the compactified dimension must be quantized. Consequently, the
three-dimensional vacua are constrained by not only the non-SUSY AdS conjecture
but also the quantization rule of the circle radius, leading to both upper and
lower bounds for the mass of the lightest neutrino as $\sqrt{2}\leq
m_\nu/\sqrt{\Lambda_4}<\sqrt{3}$ where $\Lambda_4\simeq5.06\times10^{-84}$
GeV$^2$ is the observed cosmological constant. This means that the lightest
neutrino should have a mass around $10^{-32}$ eV or it would be
well-approximately massless. With this prediction, we reconstruct the light
neutrino mass matrix that is fixed by the neutrino oscillation data and in
terms of three new mixing angles and six new phases for both the normal
ordering and inverted ordering. In the situation that the light neutrino mass
matrix is Hermitian, we calculate its numerical value in the $3\sigma$ range.
