Recommendations for light-dosimetry field studies based on a meta-analysis of personal light levels of office workers

Daytime light levels are important for human physiology. Office workers spend most of their daytime inside buildings where it is unclear whether they receive healthy light levels. A recent publication presented recommendations for the minimum daytime light level for optimal human health, expressed in melanopic equivalent daylight illuminance (EDI). The current paper assesses whether this recommended daytime light level is achieved by office workers through a meta-analysis of personal light levels of office workers, obtained from light-dosimetry field studies. From our literature search, we identified nine eligible papers. These papers comprised data from studies in one or multiple office buildings, over one or more seasons, from 1 to 62 participants, and for 19 to 564 workdays. After analysing the data, we found that in none of the offices the recommended minimum light level of 250 melanopic EDI was met for the entire day. Only 1 out of 6 median and 6 out of 13 mean reported personal light levels were above this recommended value. Unfortunately, these conclusions are less groundbreaking than we hoped for, due to large differences between study protocols. This resulted in a large variety of (unreported) study characteristics (i.e. light data, light-dosimeter, participant, building and environment) which complicated a fair comparison between the different studies. To facilitate meta-analyses of light-dosimetry field studies, we introduce recommendations for data collection and reporting in light-dosimetry field studies. We based these recommendations on the gaps identified from our meta-analysis, supplemented by recommendations from other papers.