LIGHTING | BEHAVIOURAL EFFECTS The section of the Arup London office with Ledmotives spectrally tunable lighting system installed Tunable lighting Currently, the most common artificial light sources are fluorescent lights and white LEDs, which are all static sources with spectra very different from natural daylight. The recent invention of narrow-band LEDs enables the development of spectrally tunable light sources that can generate illuminations with arbitrary spectral shapes, and so mimic daylight spectral patterns or create tailored dynamic spectral sequences according to end-user needs. Light condition Duration Dates Photopic lux Melanopic lux CCT Baseline (fluorescent lights) Two weeks 18 February to 3 March Static (350 lux) Static (160 lux) Static (3,534K) Sequence A Two weeks 4-17 May Changing (500 lux-300 lux) Changing (450 lux-160 lux) Changing (6,000K-2,500K) Sequence B Two weeks 18-31 March Static (350 lux) Changing (450 lux-170 lux) Static (3,534K) Baseline (mimicking fluorescent lights) One week 1-7 April Static (350 lux) Static (160 lux) Static (3,534K) Real-time daylight matching Two weeks 8-19 April Changing Changing Changing Table 1: Summary of the trials light conditions Spectral power distribution (W.nm-1) 0.07 0.8 0.7 0.6 y 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 x Figure 1: CIE 1931 xy coordinates of the seven channels that define the colour gamut (left) and the preset SPDs of the seven LED channels (right) CIBSE Dec19 pp14-17 ARUP Lighting Supp.indd 15 0.06 0.05 0.04 0.03 0.02 0.01 0.00 400 450 500 550 600 Wavelength (nm) 650 700 750 Previous studies have compared the performance of individual subjects under different artificial lighting conditions. Such studies, though, have used only two types of white light, both fixed in time cool, blue-enriched fluorescent light and warm fluorescent light and have not exploited the novel spectral flexibility offered by multichannel LED light sources. In this study, and for the first time in a real office setting (Arups London headquarters), the behavioural effects of a dynamic, spectrally tunable lighting system were investigated. The study included assessments of alertness, mood, sleep quality, performance and mental effort of the occupants, plus other responses to different dynamic illumination conditions, in a nine-week intervention. The aim was to assess whether sculpting different spectral power distributions (SPDs) of light may bring measurable benefits in terms of wellbeing and productivity in an indoor workplace. More generally, we wanted to understand better the behavioural effects of different lighting conditions in indoor environments and raise awareness of the importance of a circadian lighting approach. The area selected for the study, shown in the image above, measured around 160m2 and involved the working desks of 24 people. A set of 36 downlight luminaires containing Ledmotive (model VEGA07) tunable light engines were installed into ceiling panels, alongside the pre-existing fixed fluorescent light tubes. These comprised 48 commercial monochromatic LEDs arranged in seven channels, each with a distinct peak wavelength, spread over the visible spectrum. External light sources were blocked by covering the windows along one wall completely. www.cibsejournal.com December 2019 15 22/11/2019 14:56