  The softness parameter is based on the relative intensity of several optical
emission lines emitted by the gas ionized by young massive star clusters and
can be used to derive the equivalent effective temperature (T*) in those
objects whose stellar population cannot be resolved. This method has several
uncertainties due to the disagreement between different synthesis model
atmospheres but it is robust to study the relative variations between objects.
Following the 2D photoionization models of the giant HII region NGC 595
(P\'erez-Montero et al. 2011) we show that the determination of T* with the
softness parameter is also robust in different regions of a same object with
large variations in the geometry of the gas and in the dust-to-gas ratio.
