The charge deposition process in tubular channel ferroelectrets, (i. e. voided FEP polymer films with internal electric charges) has been studied using a combination of near-UV fluorescence light emission imaging and non-destructive space charge measurements with the laser intensity modulation method (LIMM). By galvanically isolating the diode laser from the detection circuit, the LIMM sensitivity was improved by nearly one order of magnitude. It was shown that the onset of light emission as a function of charging voltage precisely correlates with the deposition of space charge. This confirms previous studies where the presence of space charge was indirectly detected from the sample's piezoelectric properties.