Recebido em 16/8/05; aceito em 2/3/06; publicado na web em 26/9/06A new procedure to find the limiting range of the photomultiplier linear response of a low-cost, digital oscilloscope-based timeresolved laser-induced luminescence spectrometer (TRLS), is presented. A systematic investigation on the instrument response function with different signal input terminations, and the relationship between the luminescence intensity reaching the photomultiplier and the measured decay time are described. These investigations establish that setting the maximum intensity of the luminescence signal below 0.3V guarantees, for signal input terminations equal or higher than 99.7 ohm, a linear photomultiplier response.