  We present a study of radiative transfer in dusty, clumpy star-forming
regions. A series of self-consistent, 3-D, continuum radiative transfer models
are constructed for a grid of models parameterized by central luminosity,
filling factor, clump radius, and face-averaged optical depth. The temperature
distribution within the clouds is studied as a function of this
parameterization. Among our results, we find that: (a) the effective optical
depth is smaller in clumpy regions than in equivalent homogeneous regions; (b)
penetration of radiation is drive by the fraction of open sky (FOS) -- which
measures the fraction of solid angle which is devoid of clumps; (c) FOS
increases as clump radius increases and filling factor decreases; (d) for FOS >
0.6-0.8 the sky is sufficiently open that the temperature is relatively
insensitive to FOS; (e) the physical process by which radiation penetrates is
streaming between clumps; (f) filling factor dominates the temperature
distribution for large optical depths, and at small clump radii for small
optical depths; (g) at lower optical depths, the temperature distribution is
most sensitive to filling factors of 1-10 per cent, in accordance with many
observations; (h) direct shadowing can be important approximately one clump
radius behind a clump.
