Photo: Gerry Johansson
A post-occupancy evaluation of the first LEED Platinum building in the US, the Philip Merrill Environmental Center, shows very high satisfaction with daylight, despite concerns with visual discomfort (Heerwagen and Zagreus, 2005). This suggests that people may value the psychological benefits of daylight even when daylight creates difficulties for work due to glare and uneven light distribution.
Certainly, the kinds of visual tasks we perform in today’s work environments are very different from our ancestors’ daily tasks. Cooking, tool making, conversing, foraging, and hunting could be effectively carried out over a wide range of luminous conditions. In contrast, reading and computer work requires a much greater degree of visual acuity that may be more difficult in some daylit environments. Yet, a uniformly lit environment that may be appropriate for office work lacks the psychological, and perhaps biological, value of daylight.
Attitudes toward Daylight and Electric Light
A study of office workers in a Seattle high-rise building asked respondents to compare the relative merits of daylight and electric light for psychological comfort, general health, visual health, work performance, jobs requiring fine observation, and office aesthetics (Heerwagen and Heerwagen, 1986). The results show that the respondents rated daylight as better than electric light for all variables, especially for psychological comfort, health and aesthetics. They rated daylight and electric light as equally good for visual tasks.
Further, research in hospital settings, looking at the relationship between room daylight levels and patient outcomes, found that bipolar patients in bright, east-facing rooms stayed in the hospital 3.7 fewer days on average than those in west-facing rooms (Benedetti and others, 2001). Similar results were found by Beauchamin and Hays (1996) for psychiatric in-patients; those in the brightest rooms stayed in the hospital 2.6 fewer days on average. However, neither of these studies provides data on the actual light levels in the patient rooms or light entering the retina, so it is difficult to draw conclusions about exposure levels.
More recent research in a Pittsburgh hospital actually measured room brightness levels. Walch and others (2005) studied 89 patients who had elective cervical and spinal surgery. Half the patients were located on the bright side of the hospital, while the other half were in a hospital wing with an adjacent building that blocked sun entering the rooms. The study team measured medication types and cost as well as psychological functioning the day after surgery and at discharge.
The researchers also conducted extensive photometric measurements of light in each room, including light levels at the window, on the wall opposite the patient’s bed, and at the head of the bed (which presumably would have been at or near the patient’s eye level). The results showed that those in the brighter rooms had 46% higher intensity of sunlight. Patients in the brightest rooms also took 22% less analgesic medicine/hr and experienced less stress and marginally less pain. This resulted in a 21% decrease in the costs of medicine for those in the brightest rooms. The mechanisms linking bright light to pain are currently unknown, however.
Other potential benefits of indoor daylight include improved sense of vitality, decreased daytime sleepiness and reduced anxiety. For example, a large-scale survey of office worker exposure to light during the winter in Sweden shows that mood and vitality were enhanced in healthy people with higher levels of exposure to bright daylight (Partonen and Lönngvist, 2000). Another study shows that a half-hour exposure to bright daylight by sitting adjacent to windows reduced afternoon sleepiness in healthy adult subjects (Kaida et al., 2006). In that study, daylight levels ranged from about 1,000 lux to over 4,000 lux, depending upon sky conditions. Kaida et al. found that daylight was almost as effective as a short nap in reducing normal post-lunchtime drowsiness and increasing alertness.