A Short Nap and Natural Bright Light Exposure Improve Positive Mood Status

National Institute of Occupational Safety and Health, Kanagawa, Japan.
Industrial Health (Impact Factor: 1.12). 04/2007; 45(2):301-8. DOI: 10.2486/indhealth.45.301
Source: PubMed


While the effects of a short nap on performance and arousal level have been well investigated, less attention has been paid to its effects on mood status. The aim of the present study was to examine the effects of a short nap and natural bright light exposure on mood status. Participants were 16 healthy females who were on average 38.1 (SD = 2.68) yr old. From 11:00 to 12:00, the participants carried out a set of tasks twice with baseline lighting (<100 lux). From 12:40 to 13:10, they were subjected to three experimental conditions: control (<100 lux), natural bright light (>2,000 lux), and a 20-min nap. From 13:10 to 16:10, the tasks were repeated six times with the baseline lighting. To measure mood status, multiple visual analogue scales (to measure anxiety, sadness, anger, confusion, apathy, fatigue, and sleepiness) and the Mood Check List 3 (MCL-3) (to derive "pleasantness", "satisfaction" and "relaxation") were employed. The results showed that brief (30 min) natural bright light exposure improved one dimension of mood status, "pleasantness". A short nap also improved dimensions of mood status ("pleasantness", "satisfaction", and "relaxation"). These results suggest that the proper application of both natural light and a short nap shifts the mood status to the positive/favorable side.

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    • "The combination of bright light exposure and caffeine intake may scale down melatonin secretion (hormone associated with sleep) and increase alertness, body temperature and performance after having sleep deprivation in the previous night (Wright et al. 2000). There are even suggestions that short duration of bright light exposure after midday napping can help prevent sleep inertia (Phipps-Nelson et al. 2003), improve mood stability, alertness and performance (Kaida et al. 2007), and even beneficial for social interaction and job satisfaction at the workplace (Judge and Ilies 2004). However, there is no consensus on bright light effects since there is also a report that emotional stability and sleepiness are worsened with only the exposure to bright light (Burgess et al. 2002). "
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    • "In other words, we hypothesized that participants would feel more vital when they had experienced relatively more light. We had, however, no clear hypotheses concerning the relationship between light exposure with tension, positive and negative affect as e in contrast to potential activating effects -earlier findings on affective improvements under bright light have been inconsistent (e.g., Baron, Rea, & Daniels, 1992; Daurat et al., 1993; Hubalek et al., 2010; Kaida, Takahashi, & Otsuka, 2007; Partonen & Lönnqvist, 2000; Smolders et al., 2012). As earlier laboratory-based experiments have revealed time and mental status-dependent effects during daytime (e.g., Smolders et al., 2012; Vandewalle et al., 2006), we also investigate whether the relationship between light exposure and vitality is equally strong throughout the day, or whether instead it depends on time of day, or on previous vitality level. "
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