  Direct photons are a powerful tool for elucidating the properties of the hot
QCD matter in heavy-ion collisions. They are conventionally estimated by
assuming prompt photon contributions in proton-proton collisions and thermal
and prompt photon contributions in heavy-ion collisions. On the other hand,
there could also be other sources of photons such as pre-equilibrium photons. I
investigate prompt, pre-equilibrium and thermal photons and their effects on
the direct photon $p_T$ spectra at CERN Large Hadron Collider energies.
