  In the episodic accretion scenario, a large fraction of the protostellar mass
accretes during repeated and large bursts of accretion. Since outbursts on
protostars are typically identified at specific wavelengths, interpreting these
outbursts requires converting this change in flux to a change in total
luminosity. The Class I young stellar object EC 53 in the Serpens Main cloud
has undergone repeated increases in brightness at 850 $\mu$m that are likely
caused by bursts of accretion. In this study, we perform two- and
three-dimensional continuum radiative transfer modeling to quantify the
internal luminosity rise in EC 53 that corresponds to the factor of $\sim$1.5
enhancement in flux at 850 $\mu$m. We model the spectral energy distribution
and radial intensity profile in both the quiescent and outburst phases. The
internal luminosity in the outburst phase is $\sim 3.3$ times brighter than the
luminosity in the quiescent phase. The radial intensity profile analysis
demonstrates that the detected sub-mm flux variation of EC 53 comes from the
heated envelope by the accretion burst. We also find that the role of external
heating of the EC 53 envelope by the interstellar radiation field is
insignificant.
