  Context. Dust is a good tracer of cold dark clouds but its column density is
difficult to quantify. Aims. We want to check whether the far-infrared and
submillimeter high-resolution data from Herschel SPIRE and PACS cameras
combined with ground-based telescope bolometers allow us to retrieve the whole
dust content of cold dark clouds. Methods. We compare far-infrared and
submillimeter emission across L183 to the 8 $\mu$m absorption map from Spitzer
data and fit modified blackbody functions towards three different positions.
Results. We find that none of the Herschel SPIRE channels follow the cold dust
profile seen in absorption. Even the ground-based submillimeter telescope
observations, although more closely following the absorption profile, cannot
help to characterize the cold dust without external information such as the
dust column density itself. The difference in dust opacity can reach up to a
factor of 3 in prestellar cores of high extinction. Conclusions. In dark
clouds, the amount of very cold dust cannot be measured from its emission
alone. In particular, studies of dark clouds based only on Herschel data can
miss a large fraction of the dust content. This has an impact on core and
filament density profiles, masse and stability estimates.
