  Structural parameters of model star clusters are measured in radial profiles
built from number-density, mass-density and surface-brightness distributions,
assuming as well different photometric conditions. Star clusters of different
ages, structure and mass functions are modelled by assuming that the radial
distribution of stars follows a pre-defined analytical form. Near-infrared
surface brightness and mass-density profiles result from mass-luminosity
relations taken from a set of isochrones. Core, tidal and half-light, half-mass
and half-star count radii, together with the concentration parameter, are
measured in the three types of profiles, which are built under different
photometric depths. While surface-brightness profiles are almost insensitive to
photometric depth, radii measured in number-density and mass-density profiles
change significantly with it. Compared to radii derived with deep photometry,
shallow profiles result in lower values. This effect increases for younger
ages. Radial profiles of clusters with a spatially-uniform mass function
produce radii that do not depend on depth. With deep photometry, number-density
profiles yield radii systematically larger than those derived from
surface-brightness ones. In general, low-noise surface-brightness profiles
result in uniform structural parameters that are essentially independent of
photometric depth. For less-populous star clusters, those projected against
dense fields and/or distant ones, which result in noisy surface-brightness
profiles, this work provides a quantitative way to estimate the intrinsic radii
by means of number-density profiles built with depth-limited photometry.
