The maximum emission of dust takes place at wavelengths longer than
100 microns if the temperature of the dust is lower than 35K. The dust
inside dense clouds without internal heating sources never attains
such a high temperature and its contribution to the emission in the
IRAS bands therefore is usually small.  The extension of wavelength
coverage up to 200 microns by ISOPHOT is thus a major advantage over
IRAS in sensitivity to very cold dust emission. The detection of the
very cold dust in the cloud cores is among the main objectives in the
ISOPHOT guaranteed time interstellar dust emission proposal where
selected nearby dark clouds are mapped using ISOPHOT C100 and C200 at
90 and 200 microns, respectively. The spatial resolution and
sensitivity of ISOPHOT are superior to IRAS. The ISO mapping
possibility allows the search for low luminosity point sources in
nearby starforming sites thus expanding our knowledge of the faint end
of the stellar luminosity function in these regions. As the luminosity
function is time dependent objects in different phases of evolution
are to be observed. We want to expand the wavelength coverage of the
guaranteed time mappings of selected dark clouds to include also 60
and 135 microns. The contribution of different dust populations with
different temperatures to the observed FIR emission can now be studied
using four wavelengths instead of two. This will make the
interpretation of the data more reliable. The contribution of
localized FIR point sources can be taken into account because making a
fully sampled sensitive 60 micron map will allow us to detect also the
point sources which were too faint for IRAS. The detection of new,
faint FIR  point sources in these clouds will provide us with
significant new information on the faint end of the luminosity
function.