CIRCADIAN LIGHTING | HUMAN RESPONSE Evaluating dynamic lighting Dynamic circadian lighting varies in colour and intensity during the day, but does it improve alertness and help people sleep? BREs Paul Littlefair and Cosmin Ticleanu describe an experiment that aims to find out C ircadian rhythms control our alertness and sleep, and the release of hormones. Daytime exposure to light, especially blue light, helps synchronise the circadian clock, enabling us to feel alert during the day and sleepy at night. Many people work in poorly daylit spaces, however, with relatively low levels of electric light, and it may be hard for their bodies to maintain their circadian rhythms. Dynamic circadian lighting is being marketed using dimmable, colour-changing LEDs to give brighter, bluer light in the middle of the day, and dimmer light with Figure 2: Office space lit by the new LED lighting at different settings 2,700K and 50% lumen output 4,000K and 40% lumen output Figure 1: Office space with the original fluorescent lighting less blue later in the day when it is time to relax. BRE carried out an experiment funded by the BRE Trust and CIBSE Research Fund to investigate the effects of dynamic lighting and its timing on human subjective assessments, activity and reported sleep. The experiment The experiment took place in an open-plan office in Norwich, UK. There was very little daylight, and the windows were small and heavily obstructed by overhangs and nearby buildings. Of the 36 people who worked in the space, 23 (19 women and four men) opted into the experiment. Initially, in 18 June 2019 www.cibsejournal.com CIBSE Jun19 pp18-20 BRE research Supp.indd 18 24/05/2019 15:18