This study assessed the Southern California Postrotary Nystagmus Test (SCPNT)-stimulated nystagmus under three conditions of indoor illumination (bright, dim, and dark), and it studied the concurrent validity of SCPNT and electronystagmographic (ENG) measures of nystagmus duration and excursion. Eighteen adult subjects received three sets of rotations to the left under different lighting conditions in a counterbalanced order. The duration and excursion of the SCPNT were monitored under the bright and dim conditions, and ENG-recorded duration, excursion, frequency, slow-phase velocity, and average intersaccadic interval were measured under all three lighting conditions. No significant differences were found between nystagmus duration or excursion under the bright and dim conditions, but highly significant differences were found between the dark condition and the other two conditions. The correlation between ENG-recorded duration and SCPNT visually monitored duration across bright and dim conditions was .73, and the correlation for excursion was .24. These results suggest that occupational therapy researchers and clinicians need not question the validity of SCPNT procedures under different indoor lighting conditions, and suggest that the concurrent validity of ENG recordings and SCPNT measures requires more study.