Seeing the Light

In addition to greenery, the natural world has something else to offer building occupants: light. Daylight synchronizes our sleep-wake cycle, enabling us to stay alert during the day and to sleep at night. Nevertheless, many institutional buildings are not designed to let in as much natural light as our mind and body need. A lack of light can be a particular problem for schoolchildren. The Swedish schoolchildren were studied in four different classrooms for a year. The research showed that the kids in classrooms with the least daylight had disrupted levels of cortisol, a hormone that is regulated by the body’s circadian rhythms.

Adequate sunlight has also been shown to improve student outcomes. In 1999 the Heschong Mahone Group, a consulting group based in California that specializes in building energy-efficient structures, collected scores on standardized tests of math and reading for more than 21, 000 elementary school students in three school districts in three states: California, Washington and Colorado. The researchers rated the amount of daylight available in each of more than 2, 000 classrooms on a scale of 0 to 5. In one school district students in the sunniest classrooms advanced 26 percent faster in reading and 20 percent faster in math in one year than did those with the least daylight in their classrooms. In the other two districts, ample light boosted scores between 7 and 18 percent.

Retirement homes can also be too dark to keep circadian clocks ticking away normally. On tests taken at six-month intervals over three and a half years, the residents of the more brightly lit buildings showed 5 percent less cognitive decline than occupants of the six darker buildings did. The additional lighting also reduced symptoms of depression by 19 percent. Providing bright daytime light, the researchers believe, could have helped restore their proper rhythms and thus have improved overall brain function.

Researchers recommend using blue light-emitting diodes (LEDs) and full-spectrum fluorescent lights in buildings during the day; both have enough blue light to trigger the circadian system and keep occupants awake and alert. After dark, buildings could switch to lamps and fixtures with longer-wavelength bulbs, which are less likely to emit light detected by the circadian system and interfere with sleep at night. “If you can give people a lighting scheme where they can differentiate between day and night, that would be an important architectural decision, ” says Mariana Figueiro, program director of the Lighting Research Center at Rensselaer Polytechnic Institute.