Light is critical to human functioning in that it allows us to see things and perform activities. But it is also important because it affects human beings psychologically and physiologically. Several studies have documented the importance of light in reducing depression, decreasing fatigue, improving alertness, modulating circadian rhythms, and treating conditions such as hyperbilirubinemia among infants (Ulrich, Zimring, Joseph, Quan, & Choudhary, 2004). Further, the presence of windows in the workplace and access to daylight have been linked with increased satisfaction with the work environment (Boyce, Hunter, & Howlett, 2003; Edwards & Torcellini, 2002). Studies also show that adequate light levels are linked to reduced medication-dispensing errors in pharmacies. Thus, incorporating light into healthcare settings can be beneficial for patients as well as the staff who work there.
This paper considers the mechanisms by which light impacts human health and performance and reviews the literature linking light (daylight and artificial light) with health outcomes in health-care settings. Studies conducted in other settings that are relevant to the discussion also are examined. Several studies have addressed the technical, architectural, and energy aspects of providing optimal lighting conditions in different areas of a healthcare facility and are not reviewed here.
HOW LIGHT IMPACTS HUMAN HEALTH AND PERFORMANCE
Light impacts human health and performance by four main mechanisms:
Enabling performance of visual tasks
Controlling the bodyâ€™s circadian system
Affecting mood and perception
Facilitating direct absorption for critical chemical reactions within the body (Boyce, Hunter, & Howlett, 2003; Veitch & McColl, 1993).
In this paper, each of these mechanisms is described and the specific impacts on human health and performance are outlined.
ENABLING PERFORMANCE OF VISUAL TASKS
The most obvious effect of light on humans is in enabling vision and performance of visual tasks. According to Boyce and colleagues (2003), the nature of the taskâ€”as well as the amount, spectrum, and distribution of the lightâ€”determines the level of performance that is achieved. Performance on visual tasks gets better as light levels increase (Boyce, Hunter, & Howlett, 2003). A study by Santamaria and Bennett (1981) shows that, if the amount and distribution of light are controlled, most everyday visual tasks (such as reading and writing) can be performed as well under artificial light sources (such as fluorescent light) as under daylight conditions. However, daylight is superior for tasks involving fine color discrimination when it is provided at a high level without glare or any reduction in task visibility caused by veiling reflections or shadows (Boyce, Hunter, & Howlett, 2003).
Another factor that affects performance on visual tasks is age, and the need for light increases as a function of age due to reduced transmittance of aging eye lenses (Edwards & Torcellini, 2002). This is significant in that the workforce in American hospitals is aging, and, therefore, there may be a need to critically assess the lighting provisions for different types of tasks performed by nurses and other staff.
The work environment for nurses and physicians in hospitals is stressful. They are required to perform a range of complex tasksâ€”charting, filling prescriptions, administering medication, and performing other critical patient-care tasks. Inadequate lighting and a chaotic environment are likely to compound the burden of stress and lead to errors. However, very few studies have focused specifically on the impact of different types of lighting conditions on staff work performance in hospitals.
One study examined the effect of different illumination levels on pharmacistsâ€™ prescription-dispensing error rate (Buchanan, Barker, Gibson, Jiang, & Pearson, 1991). They found that error rates were reduced when work-surface light levels were relatively high (Buchanan et al., 1991). In this study, three different illumination levels were evaluated (450 lux; 1,100 lux; 1,500 lux). Medication-dispensing error rates were significantly lower (2.6%) at an illumination level of 1,500 lux (highest level), compared to an error rate of 3.8% at 450 lux. This is consistent with findings from other settings that show that task performance improves with increased light levels (Boyce, Hunter, & Howlett, 2003). No studies have looked at the impact of different lighting conditions at the nursesâ€™ station on task performance or error rate. More research is needed to understand the optimal lighting requirements for supporting the complex tasks performed by nurses and physicians, especially in the context of theÂ with age.Â changing demographics of the workforce.
Reducing depressionÂ dementia
At least 11 strong studies suggest that bright light is effective in reducing depression among patients with biponight-shift work among staff. A majority of the studies have examined the impact of artificial bright light on reducing depression. Artificial light treatments usually range between 2,500 lux and 10,000 lux (Beauchemin & Hays, 1996). The treatment is believed to be effective by suppressing the onset of melatonin. Two studies have shown that exposure to natural bright light is similarly effective in reducing depression (Beauchemin & Hays, 1996; Benedetti, Colombo, Barbini, Campori, & Smeraldi, 2001). Benedetti and colleagues (2001) found that bipolar depressed inpatients in east-facing rooms (exposed to bright light in the morning) stayed an average of 3.67 days less in the hospital compared with similar patients who stayed in west-facing rooms.
There is strong evidence that exposure to bright light in the morning is more effective than exposure to bright light in the evening in reducing depression. (Beauchemin & Hays, 1996; Benedetti et al., 2001; Eastman, Young, Fogg,Â Liu, & Meaden, 1998; Lewy et al., 1998; Oren, Wisner, Spinelli, & Epperson, 2002; Sumaya, Rienzi, Deegan, & Moss, 2001; J. S. Terman, Terman, Lo, & Cooper, 2001; M. Terman, Terman, & Ross, 1998; Wallace-Guy et al., 2002).Â An experimental study that compared the effect of morning and evening light on patients with winter depression found that morning light wasÂ twice as effective as evenin light in treating SAD (Lewy et al., 1998).
Decreasing length of stay
Beauchemin & Hays (1996) and Benedetti et al. (2001) documented the impact of light on length of stay among depressed patients. A couple of other studies suggest that exposure to light may be linked to length of stay among clinically nondepressed patients as well. A retrospective study of myocardial infarction patients in a cardiac intensive-care unit treated in either sunny rooms or dull rooms found that female patients stayed a shorter time in sunny rooms (2.3 days in sunny rooms, 3.3 days in dull rooms) (Beauchemin & Hays, 1998). Mortality in both sexes was consistently higher in dull rooms (39/335 dull, 21/293 sunny).
Another study found that Veterans Health Administration medical centers located in warmer and drier climates had shorter length of stay of patients (Federman, Drebing, Boisvert, & Penk, 2000). Hospitals in colder climates had longest lengths of stay in winter and fall.
Improving sleep and circadian rhythm
A small number of studies have found that timed exposure to artificial bright light might be helpful in improving sleep and circadian rhythms. In one study, community-dwelling older adults exposed to either bright white light or dim red light on 12 consecutive days experienced substantial changes in sleep quality (Satlin, Volicer, Ross, Herz, & Campbell, 1992). Waking time within sleep was reduced by an hour, and sleep efficiency improved from 77.5% to 90%, without altering time spent in bed (Satlin et al., 1992). Two other studies showed that exposure to evening bright light was related to improved rest-activity rhythms among persons with dementia in nursing homes (Satlin et al., 1992; Van Someren, Kessler, Mirmiran, & Swaab, 1997). When the daytime environmental illumination level was increased in different living spaces of a dementia unit, it was found that, during increased illumination periods, the stability of the rest-activ-ity rhythm increased in patients with intact vision, but not in visually impaired patients (Van Someren et al., 1997).
Three studies show that providing cycled lighting (reduced light levels in the night) in neonatal intensive-care units results in improved sleep and weight gain among preterm infants (Blackburn & Patteson, 1991; Mann, Haddow, Stokes, Goodley, & Rutter, 1986; Miller, White, Whitman, Oâ€™Callaghan, & Maxwell, 1995). In one study, 41 preterm infants in structurally identical critical-care units were provided either cycled or noncycled lighting (constant light levels during the day and night) during a lengthy hospital stay. Compared to infants in the noncycled lighting condition, infants assigned to the cycled lighting condition had a greater rate of weight gain, were able to be fed orally sooner, spent fewer days on the ventilator and on phototherapy, and displayed enhanced motor coordination (Miller et al., 1995).
Sloane and colleagues (1998) found that residents in facilities with low light levels displayed higher agitation levels. La Garce (2002) studied the impact of environmental lighting interventions (full-spectrum lighting, microslatted glazed windows, and electronic controls to maintain a constant level of light intensity) on agitated behaviors among residents with Alzheimerâ€™s disease. She found a significant drop in disruptive behaviors when residents were in the experimental setting (constant light levels) rather than the control setting (varying light levels) (LaGarce, 2002).
Exposure to bright morning light has been shown to reduce agitation among elderly patients with dementia. When elderly patients with dementia were exposed to 2,500 lux for 2 hours in the morning for two 10-day periods, their agitation reduced. Patients were significantly more agitated on nontreatment days (Lovell, Ancoli-Israel, & Gevirtz, 1995).
A recent randomized prospective study assessed whether the amount of sunlight in a hospital room modifies a patientâ€™s psychosocial health, quantity of analgesic medication used, and pain medication cost (Walch et al., 2005). Patients undergoing elective cervical and lumbar spinal surgeries were admitted to the bright or the dim side of the same hospital unit postoperatively. The outcomes measured included the standard morphine equivalent of all opioid medication used postoperatively by patients and their subsequent pharmacy cost. Patients staying on the bright side of the hospital unit were exposed to 46% higher-intensity sunlight on average. This study found that patients exposed to an increased intensity of sunlight experienced less perceived stress, marginally less pain, took 22% less analgesic medication per hour, and had 21% less pain medication costs (Walch et al., 2005).
Improving adjustment to night-shift work among nurses
There are approximately 8 million workers in the United States who regularly work at night, and, for many of these individuals (e.g., nurses and physicians, airline pilots), peak functioning is critical at all times (Horowitz, Cade, Wolfe, & Czeisler, 2001). Night-shift workers not only experience loss of sleep and misalignment of circadian phase, they also suffer greater risk of gastric and duodenal ulcers and cardiovascular diseases (Horowitzet al., 2001). Their decreased alertness, performance, and patients on the unitâ€™s vigilance may be responsible for more errors on the jobÂ (Smith-Coggins, Rosekind, Buccino, Dinges, & Moser, 1997).
The timing of the sleepâ€“wake schedule and work schedule of night-shift nurses remains permanently out of phase with the natural light/dark cycle, and this causes health problems. Several studies show that exposure to intermittent bright light during the night shift is effective in adapting circadian rhythms of night-shift workers (Baehr, Fogg,& Eastman, 1999; Boivin & James, 2002; Crowley, Lee, Tseng, Fogg, & Eastman, 2003; Horowitz et al., 2001; Iwata, Ichii, & Egashira, 1997; Leppamaki, Partonen, Piiroinen, Haukka, & Lonnqvist, 2003). Exposure to bright light during the night shift may also improve mood and sleep. In one study, 87 female nurses were exposed to brief periods (4 x 20 minutes) of bright (5,000 lux) light during scheduled times every night during a 2-week night shift. The treatment alleviated the nursesâ€™ subjective distress associated with night-shift work (Leppamaki et al., 2003). In addition to bright-light exposure during the night, studies have shown that additional measures such as using dark sunglasses during the commute home and a regular early daytime sleep schedule ensure complete circadian adaptation to night-shift work (Boivin & James, 2002; Crowley et al., 2003; Horowitz et al., 2001).
Supporting vitamin D metabolism
One of the well-known beneficial photochemical process that occur this way in the body is the metabolism of vitamin D. Research shows that most of the vitamin D in the blood can only be derived by exposure to light (McColl & Veitch, 2001). The ultra violet (UV) radiation in the daylight is considered to be important for this process to occur. Most people are able to metabolize vitamin D by exposure to light. However, some people, such as chronically ill institutionalized individuals, elderly, shift workers, and those living in extreme polar latitudes, may not be able to obtain that necessary sunlight exposure. McColl and Veitch cite a couple of studies that suggest that full-spectrum fluorescent lighting might be able to support this important bodily function, but conclude that there is insufficient evidence for the use of such lighting for vitamin D metabolism (McColl & Veitch, 2001).
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