  We report Herschel/PACS photometric observations at 70 {\mu}m and 160 {\mu}m
of LRLL54361 - a suspected binary protostar that exhibits periodic (P=25.34
days) flux variations at shorter wavelengths (3.6 {\mu}m and 4.5 {\mu}m)
thought to be due to pulsed accretion caused by binary motion. The PACS
observations show unprecedented flux variation at these far-infrared
wavelengths that are well cor- related with the variations at shorter
wavelengths. At 70 {\mu}m the object increases its flux by a factor of six
while at 160{\mu}m the change is about a factor of two, consistent with the
wavelength dependence seen in the far-infrared spectra. The source is
marginally resolved at 70 {\mu}m with varying FWHM. Deconvolved images of the
sources show elongations exactly matching the outflow cavities traced by the
scattered light observations. The spatial variations are anti-correlated with
the flux variation indicating that a light echo is responsible for the changes
in FWHM. The observed far-infrared flux variability indicates that the disk and
en- velope of this source is periodically heated by the accretion pulses of the
central source, and suggests that such long wavelength variability in general
may provide a reasonable proxy for accretion variations in protostars.
