Daylight at work

Most window studies change the light and the view at once. The seven here vary the light and leave the view out of it.

The occupational health researcher Stine Daugaard measured what people actually receive. In 2019 the team fitted personal light recorders to 170 indoor workers, 151 outdoor workers and 188 night workers in Denmark and recorded continuously for a week in each season. The daytime exposure of the indoor workers exceeded 1,000 lux only intermittently in summer and never in winter. Outdoor workers in summer sat at levels comparable to those used to treat depression. On days off, the indoor workers took in more light than on working days.

The architecture researcher Irmak Turan put a price on the difference. Working with 5,154 office spaces in Manhattan in 2019, the team simulated the daylight reaching each floor individually and fed the result into a hedonic valuation model. Space with high daylight, measured as 55% spatial daylight autonomy, carried a premium of 5 to 6% over space below that line, independent of building, neighbourhood and contract characteristics. 74% of the Manhattan sample fell below the line.

The building physicist Marta Benedetti tested what automated blinds and lighting do to the body clock. 34 young office workers spent five consecutive working days in a room with automated blinds and electric lighting and five in a room with neither. Vertical illuminance was 1,177 lux in the test room, 320 lux more than in the reference room. The moment at which half the day’s light had accumulated came 50 minutes earlier, and melatonin onset and evening heat loss both moved earlier relative to habitual bedtime.

The lighting researcher Eowyn Van de Putte tested the same idea on 80 shift workers on the morning shift, one group under standard lighting and one under a melanopic equivalent daylight illuminance of 192 lux. Sleep efficiency and sleep latency improved and alertness rose. Inhibition did not.

The sleep researcher Leilah Grant held 39 sleep-restricted students under four white lights of equal photopic illuminance and different melanopic strength for eight hours in 2021. Accuracy on a two-minute addition task was 5% better under the daylight-like high-melanopic light, and motor sequence learning ran 3.2 times faster.

The architecture researcher Mohamed Boubekri and colleagues compared 22 office workers with daylight against 27 in windowless workplaces in 2014, with actigraphy on 21 of them. The daylit group slept longer and took in more light across the working week. The widely quoted figure of 46 minutes is not in the abstract and the full paper is not open to us, so the entry below carries no figure.

One clinical study is on this sheet because it reaches an endpoint an office cannot supply. The medical researcher Jeffrey Walch tracked 89 patients recovering from spinal surgery on the bright and dim sides of one hospital unit in 2005. The bright side took in 46% more sunlight, and the patients there used 22% less analgesic medication per hour at p = 0.047.

Grant worked with students and Van de Putte with shift workers in an industrial setting. Neither is an office. Daugaard and Turan measured offices as they stand, 170 workers and 5,154 Manhattan spaces. 2 studies changed the light and then measured the people, Benedetti’s 34 and Boubekri’s 49.