  We investigate how significant the spiral structure is on calculations
concerning radiative transfer in dusty spiral galaxies seen edge-on. The widely
adopted exponential disk model (i.e. both the stars and the dust are
distributed exponentially in the radial direction and also perpendicular to the
plane of the disk) is now subject to a detailed comparison with a realistic
model that includes spiral structure for the stars and the dust in the disk. In
particular, model images of galaxies with logarithmic spiral arms are
constructed, such that the azimuthally averaged disk is exponential in radius
and in height, as the observations suggest. Then, pure exponential disk models
(i.e. with no spiral structure) are used to fit the edge-on appearance of the
model images. As a result, the parameters derived after the fit are compared to
the real values used to create the spiral-structured images. It turns out that
the plain exponential disk model is able to give a very good description of the
galactic disk with its parameters varying only by a few percent from their true
values.
