Bolometric light detectors provide an efficient method to collect light signals at small thresholds in cryogenic experiments and are being exploited in present and next-generation experiments for the search of Dark Matter and Neutrinoless Double Beta Decay. In this paper, we discuss the performance of sample light detecting bolometers made up of a ultra-pure Ge slab read by a high impedance thermistor, which were assembled and tested at very low temperatures, below 30 mK; we report about signal amplitude, signal to noise ratio, energy resolution and reproducibility.