Preliminary results on the influence of workplace lighting on transitory mood and subjective sleepiness

Abstract

Light affects human lives in several ways. The visual effects of lighting are related to visual performance, while the non-visual or psycho-biological effects involve health and well-being. Their action spectrum curves are also different; the visual peak efficiency lies in the yellow-green wavelength region while the maximum biological sensitivity lies in the blue region of the spectrum. Thus, lighting designers can use the color of light as well as its level to provoke psychological and physiological states such as alertness or relaxation when needed. In this regard, the spatial distribution of light is also important since there is a denser distribution of melanopsin, the circadian photoreceptor, in the inferior part of the retina, which makes an important difference between light reaching the eye from above than from below. Preliminary data from a simulated laboratory experiment where the investigation of the influence of level, color and spatial distribution of light on transitory mood and sleepiness of office workers are presented. The aim was to identify the lighting conditions that favor productivity without deteriorating wellbeing. The subjective sleepiness was assessed by the Epworth Sleepiness Scale and the transitory mood by the Scale for Mood Assessment. The laboratory setup consisted of two office workplaces separated by a wood panel, lit with different color temperature lamps (3000/4000K). Two lighting levels were provided by a general lighting from compact fluorescent lamps (Eh 500 lx, Ev 200 lx) and the other by adding a wall washer lighting from leds tubes on the front wall (Eh 800 lx; Ev 900 lx). These conditions were randomly administered and each of the four lasted 1,5h. The analyses were performed on 76 evaluations. The outcomes of two groups were compared based on 20 assessments carried out on a printed format and the other on a computer screen.Based on the computation of three indices of subjective sleepiness, transitory mood and perception of lighting, the results show that the highest mood was reached under the warm light-higher level, while the lowest occurred with cool light-lower level. The chance of dozing during the experiment was higher in the cool light-lower level and less in the warm- lower level. The mean values for warm and cool lighting both with the higher level were similar. No statistically significant differences between the two groups were found for mood nor sleepiness.The appraisal of the lit space as well as the visibility conditions were better evaluated under the warm light-higher level, and statistically significant differences were found between the groups, being better on the printed assessment test. Nevertheless, more visual symptoms were reported by this group. The highest number of symptoms occurred under the cool light-higher level.In conclusion, the results show that the color of light is important for transitory mood, and the lighting level for alerting effects. A preference for warm lighting with higher level was displayed.