We have used the discrete‐dipole approximation (DDA) method, implemented as a modified version of the DDSCAT program of Draine and Flatau, to calculate 3D light scattering intensity diagrams for individual oxide particles present in Czochralski silicon wafers. The particles were either octahedra or plates with normalized sizes x=0.01–5. The signals that would be measured for light scattered through 90° or 180° were determined from the diagrams, these angles corresponding to the cases of light scattering tomography (LST) and reflection confocal (RC) scanning infrared microscopy (SIRM), respectively. The results show that as x increases, the signal (particle image contrast) increases ∝x6 for x<∼1, but increased more slowly and in an irregular manner for x≳∼1. The signal also depends markedly on the particle shape and orientation. These findings demonstrate the difficulty of deducing quantitative data, e.g., individual particle sizes, from SIRM image contrasts. However, they also indicate the type of measurements that need to be made and provide a basis for the quantitative interpretation of the experimental results. © 1996 American Institute of Physics.