||An experiment to investigate peripheral detection performance during a driverâ€™s transition between lit and unlit sections of road was undertaken. The results suggest that when a driver moves from a lit to an unlit section of road their detection performance decreases almost immediately to that expected for the conditions of the unlit section and that there is no significant change in the subsequent 20-minute period. Tests were conducted at three luminances (0.1, 1.0 and 2.0 cd/m2): while an increase from 0.1 to 1.0 cd/m2 improved detection, a further increase to 2.0 cd/m2 did not. Lighting of two S/P ratios (0.65, 1.40) was examined at 1.0 cd/m2: this did not suggest an effect on detection performance. Taken together, these results suggest that, in the current context, visual performance reached a plateau at 1.0 cd/m2.