SLEEPINESS OFTEN OCCURS IN THE EARLY MORN- ING AND AFTERNOON.1,2 INCREASED SLEEPINESS HAS BEEN RECOGNIZED NOT ONLY AS A CAUSE OF automo-

SLEEPINESS OFTEN OCCURS IN THE EARLY MORNING AND AFTERNOON.1,2 INCREASED SLEEPINESS HAS BEEN RECOGNIZED NOT ONLY AS A CAUSE OF automobile accidents, but also as a detriment to work efficiency in our business life.3-6 Several strategies have been examined as methods for controlling this sleepiness, such as taking caffeine,7-9 blowing cold air on the face,10 listening to the radio,10 chewing gum,11 and face-washing.9 In particular, short naps (less than 30 minutes) and exposure to bright light have attracted researchers’ attention. Many studies have reported that a short nap (or “power nap”) facilitates recovery from drowsiness.8,12-20 Although some researchers warn of a risk of heart attack resulting from drastic fluctuation of the autonomic nervous system on awakening,21,22,23 it seems clear that a short nap has beneficial effects on work efficiency.13 The effect of bright light exposure (above 1000 lux) on arousal level has also been well documented.9,24-40 In a clinical setting, bright light is commonly used for antidepressant therapy to treat seasonal affective disorder36,37 or for resetting internal biologic clocks.38 In a work setting, bright light is effective in controlling workers’ arousal level in nighttime.39 Although the beneficial effects of a short nap and bright light are obvious, there are some difficulties associated with incorporating these strategies into real work settings. Firstly, not everyone can make enough time or create a safe space to take a nap in the workplace. Secondly, not every company can install adequate lighting systems in all workplaces, mainly due to financial considerations. Moreover, the duration of bright light exposure used in many previous studies (longer than 1 hour)24,27,32-34,36 would be too long to introduce into normal work hours (i.e., 8 hours), since most workers typically take only a 1-hour break for lunch. The present study, therefore, attempted to examine the effects of a short (30 minute) natural bright light exposure at lunchtime on workers’ performance and arousal levels. Subjective sleepiness and physiologic arousal measured by electroencephalography were evaluated to quantify “arousal levels” in this study. The advantages of natural light are primarily considered to be its inexpensiveness and convenience. Everyone can afford free natural light if the weather is fine. In addition, 30 minutes of exposure is compatible with the limited lunchtime of working individuals. If natural bright light exposure is effective for improving arousal levels, the subsequent area of interest would be whether natural bright light or a short nap is most effective. To elucidate this issue, the comparison between natural bright light and a short nap was also conducted in the present study. The hypothesis of the present study was that natural bright light would improve arousal level in the afternoon.