The main purpose of the present investigation was to find out if changes in intensity of a bright light source differentially affected nighttime performance when the intensity was varied at the source compared to moving participants in relation to the source. Previous research has not studied distance from source specifically as an independent variable. The present study also attempted to find out if duration of light exposure would influence performance tasks as previous findings suggest (McIntyre et al. 1989; Lewy et al., 1980). Duration of exposure had not been systematically examined as an independent variable until Baker (1999) studied the effects of both 15-min and 60-min durations on mental performance. Light levels of baseline (>100- lux, normal room lighting). 1,000, and 2.000 lux were paired with 2 different duration conditions (15-min prior and 60-min continuous), and two different distance conditions (Fixed and Moved distance). Twenty volunteers completed tests of mathematical reasoning, logical reasoning, vigilance, memory recall, and memory recognition between 2400 hrs and 0100 hrs once a week for six consecutive weeks. The results showed that the method of varying light intensity does seem to matter if only for the 2,000-lux intensity and, overall, the 15-min duration condition resulted in better performance than the 60-min duration condition. The present study produced inconclusive results in regard to the duration of exposure and in regard to the method of varying light intensity. However, it is possible to conclude that the method of varying light intensity probably does impact performance. Furthermore, the present study raises two serious methodological concerns in regards to the speed-accuracy tradeoff problem and in regard to the standardisation of task type.