The importance of including position and viewing direction when measuring and assessing the lighting conditions of office workers.

BACKGROUND: Light and alertness studies have applied different measurement methodologies to determine lighting conditions. However, it has been demonstrated that researchers rarely measure or describe the lighting conditions of their studies in sufficient detail to generalize conclusions or derive universal guidelines. OBJECTIVE: Part I of this paper summarizes the current measurement methodologies used in light and alertness studies to potentially identify methodological issues. Part II determines the differences in lighting conditions for different viewing directions within an office environment. METHODS: A literature review (part I) and both experimental studies and an observational study (part II) were undertaken in this study. RESULTS: Part I demonstrates that most light and alertness studies include photometric quantities; however, it is recommended that one should measure radiometric quantities as well. Further, the light measurements should be performed at the individual level. Part II demonstrates large differences in lighting conditions between viewing directions. For example, when looking toward the window, vertical illuminances were at least 12 times higher when compared to looking in the opposite direction. CONCLUSIONS: Our findings suggest that when analysing or designing an office environment, office workers' positions and viewing direction should be included in the determination of personal lighting conditions.