LRC professors develop daylighting design guide for school students

The body's internal clock is responsible for regulating the timing of our sleep and other daily biological cycles, called circadian rhythms. During school months, however, teenagers miss out on essential morning light needed to stimulate the 24-hour biological clock. For this reason, professors at Rensselaer Polytechnic Institute Lighting Research Center (LRC) have developed a daylighting design guide that balances the photobiological benefits of daylighting with well-known daylight design techniques that can be applied in schools.

"When done properly, these dynamic interiors support human health and activities while also reducing energy demand," said Russ Leslie, LRC associate director, professor, and lead author of the newly published book, Patterns to Daylight Schools for People and Sustainability.

The book is the culmination of a research project that began in 2008, sponsored by the U.S. Green Building Council (USGBC) and, in part, by a grant from a Trans-National Institutes of Health Genes, Environment and Health Initiative (NIH-GEI), to scientifically quantify the impact of daylight design on students' well-being and performance in K-12 schools and investigate the underlying biological mechanisms associated with this possible link.

"When light enters the human eye, the visual system responds differently to it than does the circadian system, which is much more sensitive to short-wavelength (blue) light and needs more light to be activated than the visual system," said Mariana Figueiro, Ph.D., LRC program director, associate professor, and principal investigator. "Today's rigid school schedules requiring teenagers to be in class early in the morning causes them to miss the essential morning light needed to stimulate the circadian system, which regulates body temperature, alertness, appetite, hormones and sleep patterns."

Most schools typically do not provide adequate electric light or daylight to fully stimulate the circadian system, according to Figueiro. However, if designers provide sufficient daylight, which contains ample short-wavelength light, in classrooms, school buildings will be able to provide more circadian stimulation and, therefore, promote improved health, performance and well-being.

Leslie recommends architects use the new book to identify potential approaches, or "patterns," to daylight schools. Similar to traditional architectural pattern books, this one gives model designs that can be adapted to a particular school project. The book includes a "daylighting dashboard" to quickly compare the patterns graphically with indicators of cost, comfort, the visual environment, and energy use. The publication offers conceptual daylight approaches for the three most common spaces in schools: classrooms, corridors, and gymnasiums.

LRC Senior Research Specialist Aaron Smith, LRC Lead Research Specialist Leora Radetsky, LRC Associate Professor Mariana Figueiro, and LRC graduate student Lisa Yue contributed as co-authors of Patterns to Daylight Schools for People and Sustainability.

Setting the body's clock

The human biological clock runs with a period slightly greater than 24 hours. Each morning when we receive sufficient light, the biological clock is "reset" to match the 24-hour solar day. Bright days and dark nights are ideal for regulating this biological system, called the circadian system. One of the biological functions regulated by the circadian system is the production of melatonin, a hormone produced in the evening and under conditions of darkness that indicates to the body when it is nighttime. Sleep typically occurs about two hours after the onset of melatonin.

Field tests quantify the impact of daylight design on students

Figueiro and LRC Director Mark Rea, Ph.D., performed a series of field tests in 2009 funded by USBGC and NIH-GEI to examine the impact of removing morning light on teens' melatonin onset and sleep times, as well as the seasonal impact and the increased evening light exposure during the spring months on teens' melatonin onset and sleep times.

Each subject wore a Daysimeter™, a small, head-mounted device developed by the LRC to measure an individual's exposure to daily "circadian light," as well as rest and activity patterns. The definition of circadian light is based upon the potential for light to suppress melatonin synthesis at night, as opposed to measuring light in terms of how it stimulates the visual system.

"The field tests support the general hypothesis that the entire 24-hour pattern of light/dark exposure influences synchronization of the body's circadian clock with the solar day and thus influences teenagers' sleep/wake cycles," explained Figueiro. "As a general rule, teenagers should increase morning daylight exposure year round and decrease evening daylight exposure in the spring to help ensure they will get sufficient sleep before going to school."