  Extended Red Emission (ERE) has been detected in many dusty astrophysical
objects and this raises the question: Is ERE present only in discrete objects
or is it an observational feature of all dust, i.e. present in the diffuse
interstellar medium? In order to answer this question, we determined the blue
and red intensities of the radiation from the diffuse interstellar medium (ISM)
and examined the red intensity for the presence of an excess above that
expected for scattered light. The diffuse ISM blue and red intensities were
obtained by subtracting the integrated star and galaxy intensities from the
blue and red measurements made by the Imaging Photopolarimeter (IPP) aboard the
Pioneer 10 and 11 spacecraft. The color of the diffuse ISM was found to be
redder than the Pioneer intensities, contrary to that expected for scattered
light (Diffuse Galactic Light [DGL]). The red DGL was calculated using the blue
diffuse ISM intensities and the approximately invariant color of the DGL
calculated with the DGL model. Subtracting the calculated red DGL from the red
diffuse ISM intensities resulted in the detection of an excess red intensity.
This represents the likely detection of ERE in the diffuse ISM since H-alpha
emission cannot account for the strength of this excess and the only other
known emission process applicable to the diffuse ISM is ERE. Thus, ERE appears
to be a general characteristic of dust. From the correlation between N_HI and
ERE intensity the ERE photon conversion efficiency was estimated at 10 +/- 3%.
