Lighting in offices: lamp spectrum and brightness

In UK offices, a ubiquitous target for lighting ‘design’ is an illuminance of 500 lux on the working plane. This article questions the basis for the 500 lux standard and suggests that a reduced illuminance would not affect visual performance. However, lighting design should also consider expectations and if a reduced illuminance leads to perceived gloom then this could affect motivation to carry out work tasks. Evidence is presented which suggests that the brightness of a space may be maintained, despite a reduction in illuminance, through the choice of lamp spectral power distribution.