  We continue the investigation of mesons in terms of the spectral integral
equation initiated before [hep-ph/0510410, hep-ph/0511005] for the $b\bar b$
and $c\bar c$ systems: in this paper we consider the light-quark ($u, d,s$)
mesons with masses $M\le 3$ GeV. The calculations have been performed for the
mesons lying on linear trajectories in the $(n,M^2)$-planes, where $n$ is the
radial quantum number. Our consideration relates to the $q\bar q$ states with
one component in the flavor space, with the quark and antiquark masses equal to
each other, such as $\pi(0^{-+})$, $\rho(1^{--})$, $\omega(1^{--})$,
$\phi(1^{--})$, $a_0(0^{++})$, $a_1(1^{++})$, $a_2(2^{++})$, $b_1(1^{+-})$,
$f_2(2^{++})$, $\pi_2(2^{-+})$, $\rho_3(3^{--})$, $\omega_3(3^{--})$,
$\phi_3(3^{--})$, $\pi_4(4^{-+})$ at $n\le 6$. We obtained the wave functions
and mass values of mesons lying on these trajectories. The corresponding
trajectories are linear, in agreement with data. We have calculated the
two-photon decays $\pi\to \gamma\gamma$, $a_0(980)\to \gamma\gamma$,
$a_2(1320)\to \gamma\gamma$, $f_2(1285)\to \gamma\gamma$, $f_2(1525)\to
\gamma\gamma$ and radiative transitions $\rho\to\gamma\pi$,
$\omega\to\gamma\pi$, that agree qualitatively with the experiment. On this
basis, we extract the singular part of the interaction amplitude, which
corresponds to the so-called "confinement interaction". The description of the
data requires the presence of the strong $t$-channel singularities for both
scalar and vector exchanges.
