Optimal Lighting Conditions for Office Workers from the Perspective of Non-visual Effects

Abstract

Optimal lighting conditions for office environments were examined with respect to effects on productivity, alertness, subjective responses, sleep composition, and circadian rhythms of melatonin and body temperature. Participants were 10 healthy male students (mean age: 24.1 ± 1.1). Three lighting conditions were employed: (1) 750 lx and 5000 K, kept constant from 9:00 to 18:00 ( JIS mode); (2) 400 lx and 5000 K, kept constant from 9:00 to 18:00 (SE mode); and (3) 750 lx and 6000 K from 9:00 to 14:00, followed by the eco circadian light control program (ECLCP), in which light intensity and correlated color temperature were gradually lowered to 400 lx and 4000 K from 14:00 to 17:00 and then kept constant until 18:00. Participants stayed in the chamber for approximately 48 h. They performed simulated office tasks from 9:00 to 17:30 with the exception of short breaks for rest and lunch. Simulated office work comprised two parts: (1) performance of the contingent negative variation (CNV) paradigm, and (2) performance of the Cognitive Performance Test of Productivity (CPTOP). Four sequential measurements in each set were employed: (1) subjective evaluation of the environment on a rating scale (3 min), (2) CNV paradigm (15 min), (3) CPTOP (30 min), and (4) rest (15 min). Two sets were carried out in the morning and three sets in the afternoon. Participants were exposed to dim light from 19:30 to 25:00, and saliva samples were taken every 30 min from 20:00 to 25:00 to analyze melatonin concentration. Participants went to bed at 25:30 (< 3 lx) and got up at 7:30. Rectal temperature was recorded during sleep from 25:30 to 7:30. Sleep architecture was also evaluated during this time period on the second night. The experimental conditions on the second day were identical to those on the first day. Data obtained on the second day were used for analysis. Average CNV amplitude in SE mode (400 lx) was significantly smaller than that in JIS mode (750 lx) and ECLCP. The number of errors in the selective response in the CNV paradigm under SE mode was significantly greater than that under JIS mode and ECLCP. The increases and decreases in rectal temperature between bedtime, nadir, and waking time were smallest in SE mode, while the increase was greatest in ECLCP. ECLCP conditions significantly advanced the phase of circadian rhythm and were associated with greater increases in melatonin compared with the JIS and SE conditions before bedtime. Polysomnograms during the first half of sleep tended to show a lower score of stage 3 sleep in SE mode compared with JIS mode and ECLCP, but did not reach the level of significance (p < 0.1).How to cite this article: Akira Yasukouchi, Naohiro Toda, and Hiroki Noguchi, (2018) ICOHS 2017Results indicate that light intensities of less than 400 lx might affect not only alertness and productivity, but also the amplitude and phase of circadian rhythms including sleep composition. Light control conditions such as ECLCP appear to maintain appropriate circadian rhythms while retaining the work ...

Non-visual effects of diurnal exposure to an artificial skylight, including nocturnal melatonin suppression

“…Studies of occupant health and well-being in built environments have recently begun to be conducted. It has been demonstrated that light, in addition to air and water quality, has a strong effect on occupant health and well-being in offices, not only from the point of view of subjective comfort, but also in terms of objective aspects or non-visual effects [15, 19, 21, 33].…”

“…Many studies have focused on the non-visual effects of light [7, 34], with application studies showing its beneficial effects on human health and well-being and how to translate scientific findings into office lighting designs [15, 19, 22, 23]. Non-visual responses include almost all physiological functions affected by photic signals from ipRGCs projected to all major retinorecipient parts of the brain [28, 35].…”

“…The increased melatonin secretion before sleep might be caused by advanced DLMO or secretion activation by light exposure in the morning. The previous studies showed that the higher intensity and/or CCT of light in the morning, the smaller the light-induced nocturnal melatonin suppression and the more advanced the circadian rhythm phase (DLMO) [15, 55, 63]. There might be psychological effects that occurred in daytime due to different light sources.…”

“…However, occupants in windowless environments or those who are situated away from windows have to depend on artificial light and have no connection to nature. Natural light and views from windows also enhance attention and cognition [14], whereas windowless environments or those with relatively low artificial light illumination negatively affect arousal level and productivity due to sleepiness [15]. Furthermore, there is no time-dependent variation in natural light and views throughout the day in windowless environments, which can increase psychological stress [16] and lower job satisfaction [17].…”

“…Canazei et al [18] determined, using a questionnaire-based approach, that an artificial skylight similar to the one used in this study had beneficial effects compared with conventional fluorescent lighting. However, in addition to psychological effects, physiological responses caused by non-visual effects or non-image-forming effects should also be considered to improve worker health, well-being, and productivity [15, 19–23]. Ours is the first study to examine the non-visual effects of artificial skylights in a simulated office environment.…”