The influence of controllable task-lighting on productivity: a field study in a factory.

This study examines whether or not a controllable task-lighting system that allows people to select high lighting levels will enhance productivity under real working conditions. For a period of 16 months a study was carried out in a luminaire factory in Finland in which such a task-lighting system was installed above 10 individual workstations. The illuminances selected by the users were recorded and productivity was monitored. Enhancing productivity can be relevant in industrial processes. The increase of productivity for the test group was +4.5% compared to a reference group, and statistically significant. The mechanism for this increase can be improved visual performance, biological effects of light, or psychological effects. Different dimming speeds were used to see whether the subjects' choices were based on illuminance or on the response of the control system. Decreasing the dimming speed of the system decreased the illuminance chosen by 13%. However, at slower dimming speeds the subjects took 55% longer to reach a given level, which suggests that they were aiming to set the lighting to their preferred level and not just pushing the button for a certain time.