SHORT COMMUNICATION Validating the Use of Wrist-Level Light Monitoring for In-Hospital Circadian Studies Anisoara C. N. Jardim, 1 Matthew D. M. Pawley, 1,2 James F. Cheeseman, 1 Mirjam J. Guesgen, 1 Christopher T. Steele, 3 and Guy R. Warman 1 1 Department of Anaesthesiology, University of Auckland, Auckland, New Zealand, 2 Institute of Information and Mathematical Sciences, Massey University, Palmerston North, New Zealand, 3 Military and Emergency Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland, USA This clinical methods comparison study describes the difference between light levels measured at the wrist (Actiwatch-L) and at the eye (Daysimeter) in a postoperative in-patient population. The mean difference between the two devices was less than 10 lux at light levels less than 5000 lux. Agreement between the devices was found to decrease as eye-level light exposure increased. Measurements at eye level of 5000 lux or more corresponded to a difference between the devices of greater than 100 lux. Agreement between the eye- and wrist-level light measurements also appears to be influenced by time of day. During the day, the measurement differences were on average 50 lux higher at eye level, whereas at night they were on average 50 lux lower. Although the wrist-level monitor was found to underestimate light exposure at higher light levels, it was well tolerated by participants in the clinical setting. In contrast, the eye-level monitor was cumbersome and uncomfortable for the patients to wear. This study provides light-exposure data on patients in real conditions in the clinical environment. The results show that wrist-level monitoring provides an adequate estimate of light exposure for in-hospital circadian studies. (Author correspondence: g.warman@auckland.ac.nz) Keywords: Daysimeter, Actiwatch-L, Environmental monitoring/instrumentation, Hospital, Light, Circadian, Entrainment INTRODUCTION Surgery, anesthesia, and hospitalization are known to cause sleep disruption (Challet et al., 2007; Gogenur et al., 2009; Murialdo et al., 1993; Njawe, 2003; Vinzio et al., 2003; Yin et al., 2005). This sleep disruption results in part from a circadian disruption due to the absence of strong entraining light-dark cycles, character- istic of the hospital environment, and the phase-shifting effects of surgery and anesthesia. The consequences include impaired immune function, reduced mood, and delayed postoperative recovery (Arjona et al., 2006, 2008; Buijs et al., 2003; Costa e Silva, 2006; Majde et al., 2005). Light is the primary zeitgeber for the human circadian clock, and light therapy has been identified as a useful therapeutic tool to treat depression, both seasonal affec- tive disorder and nonseasonal major depression (reviewed in Terman et al., 2010). Depressed in-patients housed in bright hospital rooms have been shown to have a shorter (up to 3.7 d) stay than those housed in dimly lit rooms (Beauchemin et al., 1996; Benedetti et al., 2001). This effect is not confined to patients being treated for depression. Women hospitalized with myocardial infarc- tion also spend less time in the hospital when allocated sunnier rooms (Beauchemin et al., 1998). Such studies have led to the publication of a manual for clinicians advocating the use of light therapy to treat affective dis- orders and detailing treatment protocols (Wirz-Justice et al., 2009). Despite these data, a UK-based study of 343 828 general hospital admissions showed that the duration of hospital stay does not differ between winter and summer, which might be anticipated if light exposure is important in influencing length of stay (Diffey et al.,1988). Ambient light levels in hospitals have been measured in a number of previous studies using stationary light meters (Bullough et al., 1996; Garcia-Gonzalez et al., 2008; Glotzbach et al., 1993; Gogenur et al., 2007, 2008; Wakamura et al., 2001). All of these studies have shown the presence of dampened daily light-dark cycles with low light exposure during the day and higher levels Address correspondence to Dr. Guy Warman, Department of Anaesthesiology, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand. Tel.: + 64-9-373 7599 ext 89302; Fax: + 64-9-3737970; E-mail: g.warman@ auckland.ac.nz Submitted May 5, 2011, Returned for revision June 2, 2011, Accepted July 29, 2011 Chronobiology International, Early Online: 1–7, (2011) Copyright Informa Healthcare USA, Inc. ISSN 0742-0528 print/1525-6073 online DOI: 10.3109/07420528.2011.611603  Chronobiol Int Downloaded from informahealthcare.com by University Of Auckland on 09/27/11 For personal use only.