  We use QCD kinetic theory to compute photon production in the chemically
equilibrating Quark-Gluon Plasma created in the early stages of high-energy
heavy-ion collisions. We show that the photon spectrum radiated from an
attractor evolution satisfies a simple scaling form in terms of the specific
shear viscosity $\eta/s$ and entropy density $dS/d\zeta \sim {\scriptstyle
\left(T\tau^{1/3}\right)^{3/2}}_\infty$. We confirm the analytical predictions
with numerical kinetic theory simulations. We use the extracted scaling
function to compute the pre-equilibrium photon contribution in
$\sqrt{s_{NN}}=2.76\,\text{TeV}$ 0-20% PbPb collisions. We demonstrate that our
matching procedure allows for a smooth switching from pre-equilibrium kinetic
to thermal hydrodynamic photon production.

High Energy Physics - Phenomenology;Nuclear Theory