Optically stimulated luminescence (OSL) signals from various insulators including quartz, Al2O3 : C, BeO and NaCl have been studied using the linear modulation OSL (LM-OSL) technique. LM-OSL is based on the linear increase of the stimulation light power from zero to a maximum during the measurement. The resultant OSL curve initially increases and then decays after reaching a maximum, The analysis of LM-OSL data usually assumes a linear relationship between the detrapping rate and the stimulation light intensity. However, experiments carried out using various insulators have shown that this assumption is not always correct. The initial decay rates of the blue (similar to 470 nm) light stimulated constant power OSL decay curves were examined to test the relation between the detrapping rates and the stimulation light intensity. In SiO2, Al2O3 : C and BeO a linear relation between the detrapping rates and the stimulation light intensity was observed. However the detrapping rate of the OSL signal from NaCl was non-linear. Assuming that this non-linearity can be described using a saturating exponential function, a new more general expression for the LM-OSL signal has been derived. The validity of this expression was checked using curve fitting and it was found that the new expression could describe the LM-OSL curves successfully. (C) 2001 Elsevier Science Ltd. All rights reserved.