  PHENIX has used the versatility of RHIC to map out low $p_{T}$ direct photon
production as function of collision system size and beam energy. For systems
with a size corresponding to a $dN_{ch}/d\eta$ larger than 20-30, we observe a
large yield of direct photons, a large azimuthal anisotropy with respect to the
reaction plane, and a characteristic centrality dependence of $dN_{\gamma}/dy
\propto (dN_{ch}/d\eta)^{\alpha}$, with $\alpha \sim$ 1.2. \\ In this
proceeding, we will present new results from Au+Au collisions at
$\sqrt{s_{NN}}$ = 39, 62.4 and 200 GeV. After subtracting the prompt photon
component, the inverse slope for the $p_{T}$ range from 1-2 GeV/$c$ is 250
MeV/$c$, but increases to about 400 MeV/$c$ for the range from 2 to 4 GeV/$c$.
Within the experimental uncertainty, there is no indication of a system size
dependence of the inverse slope. Furthermore, the system size dependence of the
yield, expressed through the power $\alpha$, remains independent of $p_{T}$
over the entire observed range from 1 to 6 GeV/$c$. Like the large yield and
azimuthal anisotropy, these features, while qualitatively consistent with the
emission of thermal photons from the quark gluon plasma, elude a quantitative
description through theoretical model calculations.
