Recently, a systematic comparison of SIN4S measurements with LTPL (Low Temperature Photoluminescence) spectra led us to propose a straightforward empirical calibration of the LTPL intensity versus Al content in 4H-SiC samples. In the present work we analyze the effect of the LTPL excitation power on the intensity of the Al-related features. We examine the influence of the excitation conditions on the calibration curve and determine the limitations of the method.