We employ the coupled dipole method [B. W. Kwaadgras, et al., J. Chem. Phys., 2011, 135, 134105] to calculate the orientation-dependent interaction of polarizable colloidal rods with an external electric field. We project the angular distribution function of a system of such rods on a quasi-two-dimensional slab, corresponding to the focal plane of a microscope, and show that the 3D nematic order parameter and its measurable projected analogue are very similar. We compare our results to confocal microscopy measurements on the orientation distribution function of systems of polarizable colloidal silica rods in an external electric field, demonstrating reasonably good agreement between theory and experiment without any free fit parameter.