  The direct photon emission model in relativistic nuclear colliders has been
improved in recent years for reducing the discrepancy between theoretical
estimations and experimental data and for understanding the properties of the
QCD matter. In this study, the contribution of pre-equilibrium photons are
investigated in addition to those of prompt and thermal photons in the
framework of a relativistic hydrodynamic model. The numerical simulations at an
LHC energy suggest that the pre-equilibrium photons may be relevant at
intermediate transverse momentum near the saturation momentum scale, increasing
particle spectra and reducing elliptic flow of direct photons.
