LR&T essentials
May/ June 2023
WORKING KNOWLEDGE Iain Carlile looks at two of the latest Lighting Research and Technology papers focusing on aspects of office lighting
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olf et al have investigated the lighting of home-working setups, looking at digitisation and growing flexibility in the European Labour Market. With a specific focus on German companies and workers, the authors note (from the results of a survey in July 2020) that 51 per cent of German companies partially worked from home before the COVID-19 pandemic. After the start of the pandemic the number of employees working from home increased rapidly, since 80 per cent of workplaces were partially or completely closed. The authors also point out that many homeworking setups are located in residential rooms that would have originally been intended for different tasks and functions, and therefore the lighting may not be suitable for task illuminance and healthy daytime light exposure. Undertaking a small-scale study of the home-working locations of nine office employees, it was found that illuminance levels were low in comparison to German office lighting standards, and that the melanopic equivalent daylight illuminance (MEDI) did
not achieve recommended levels for healthy daytime light exposure. Additional lighting was installed at each participant's desk to investigate the effects on their alertness. It was found that the average illuminance levels and MEDI were increased. It was also found that the participant's subjective sleepiness decreased after six hours, although the authors note the difference was not significant. Response-time improvements in a psychomotor vigilance task were achieved at the start of work and after three hours. Most participants said that they would use the additional lighting in the future, indicating that they were dissatisfied with their current lighting conditions and/or perceive an increase in lighting levels as an improvement to their homeworking conditions. The authors make various recommendations to improve the lighting in home-based workplaces, such as increased illuminance, indirect lighting to avoid glare, moving desks to lighter spaces, or working near windows. Also examining lighting within a working
environment, Van de Perre et al have studied the effects of CCT and wall luminance on observers’ brightness perception and scene preference within a controlled, windowless office environment. An experiment was conducted using a twointerval, forced choice with 20 lighting scenes derived from five different CCTs (2500K, 3075K, 4000K, 5715K, 10,000K) and four different wall luminance values (12 cd/sqm, 36 cd/sqm, 72 cd/ sqm, 120 cd/sqm). Twenty observers with normal vision took part in the study (10 women and 10 men, age range 21-58 years, with a median value of 28 years). Each observer took part in two sessions, the first to assess brightness and the second to assess preference. It was found that at equal luminances, different CCT values had no significant effect on perceived brightness. Scene preference increased as the wall luminance was increased to 72 cd/sqm, but increasing the wall luminance further to 120 cd/sqm had no significant effect on the participants’ preferences. Regarding CCT, as this was increased from 2500K to 4000K the observers' preference increased, followed by a substantial decline in preference from a CCT of 5715K to 10,000K. Iain Carlile, FSLL, is a past president of the SLL and a senior associate at dpa lighting consultants Lighting Research and Technology: OnlineFirst In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website (www.sll.org.uk) Light exposure in home-based work: Can a simple lighting system increase alertness? H Rolf, L Udovicic and S Völker
p Image of the experiment room (left) and a schematic layout of the experiment room (right) showing the approximate positions of the observer, experiment supervisor and ceiling fixtures. The latter is shown as yellow squares (Van de Perre et al)
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The effect of correlated colour temperature and wall luminance on spatial brightness and scene preference in a windowless office setup L Van de Perre, KAG Smet, P Hanselaer, M Dujardin and WR Ryckaert
sll.org.uk