Enhancement of nighttime alertness and performance with bright ambient light.

Objective levels of alertness and performance efficiency were measured in twenty-five healthy young adults during two simulated night shifts. Following the first night shift, during which all subjects worked under dim ambient light (10-20 lux), subjects were assigned to one of three ambient lighting conditions (10-20 lux, 100 lux or 1000 lux) for the second night of work. Subjects exposed to 1000 lux ambient light maintained significantly higher levels of alertness across the 8-hour shift than did subjects exposed to the dimmer lighting conditions. Cognitive performance was also significantly enhanced under the bright light condition, whereas simple reaction time was not. The findings indicate clearly that ambient lighting levels can have a substantial impact on nighttime alertness and performance and that bright ambient illumination may be effective in maintaining optimal levels of alertness during night shift operations.