This present paper deals with the spectral characterization of dusty plasmas such as those produced during ITER fusion experiments. Such plasma formed in a small radio frequency plasma reactor with acetylene was characterized using in situ Fourier transform infrared (FTIR) absorption spectroscopy and laser scattering, and ex situ transmission electron microscopy (TEM). The plasma absorbance spectra thus obtained in the visible and infrared wavelengths exhibit special features associated with the dust particle growth which absorbs and scatters IR light. This experimental absorbance behavior is reproduced using a dedicated radiation modeling based on the Mie theory and the Monte Carlo simulation. The bimodal distribution assumed for particle sizes brings the model-determined optical properties closer to the experimental dust absorbance than the normal and uniform distributions. Dust formation mechanism is further discussed comparing the experimental and simulated absorbance.