Although the use of light to treat ailments can be traced back thousands of years to ancient India, Egypt, and China, it is only in the past 25 to 30 years that issues of light and health have begun to be addressed in contemporary discussions. And only in the past 10 years have modern science and medicine started to recognize light's critical impact on human biology in myriad health-related issues now indicative of our 24-hour culture.

Why, then, has the topic of light and health moved to a more prominent focus in design, science, and medical discussions? According to Dr. George Brainard of Thomas Jefferson University, Department of Neurology in Philadelphia, one of the leading researchers on the subject of light and health for the past 25 years, there are three principal reasons: the seminal discovery in 1980 that light could suppress the production of melatonin (a hormone secreted by the pineal gland and thought to be concerned with regulating the reproduction cycle); the 2001 discovery of different photoreceptors in the human eye that govern and distinguish between day vision and night vision; and the 2002 discovery of the photosensitive ganglion cells in front of the human eye's retina that indicate there are photoreceptors that work independently of the vision system and have significant impact on our endocrine system (glands that secrete hormones directly into the blood).

While these discoveries are paramount, present day issues related to lighting design also are contributing to this increased awareness. Fred Oberkircher, associate professor at the Texas Christian University Center for Lighting Education in Fort Worth, Texas, observes the increased awareness as a general societal recognition of health issues combined with the need to reduce energy use. Coupled with the discovery of the ganglion cell receptor, the dialogue begins to reach a broad spectrum of people, and no longer is relegated to a niche discussion.

AREAS OF INVESTIGATION There are several principal areas of investigation pertaining to light and health related issues. They include: study of the circadian cycle; sleep disorders; seasonal affective disorder, commonly referred to as SAD; eyestrain; visual performance; tissue damage to eyes and skin because of ultraviolet (UV) radiation; and vitamin D deficiency. There also are studies related to the correlation between light and specific types of cancers, although currently researchers agree there is not enough data gathered to make the findings conclusive. As Dr. Jamie Zeitzer, assistant professor of psychiatry at Stanford University and the VA Palo Alto Health Care System, points out, there are as many levels to study these topics as there are research areas, ranging from molecular DNA and cell structures to human biology and biochemistry.

GATHERING DATA—BIOLOGY OR PSYCHOLOGY? One of the greatest obstacles facing light and health related research has been how to distinguish between biology and psychology and prove that both are equally relevant. Zeitzer states, “If you can show something at the biological level there's more credence to it. Whenever you talk about something at the psychological level people always think of it as a more labile concept. For years physicians didn't take insomnia as a serious problem, they viewed it as a psychological phenomena rather than a physiological one. A lot of the effort in the past 20 years has been trying to quantify these issues as an actual biological process.”

CIRCADIAN CYCLES No matter the area of research, it is fair to say that all these investigations find their roots in the circadian cycle. “In less than two generations we have totally changed our relationship to the circadian rhythms of life,” Oberkircher says. “We have experienced two huge changes in the last 100 years—the electric light bulb and air conditioning. The question is what does it mean when we are no longer governed by the sun coming up and the sun going down? What are the ramifications of our choosing to ignore this natural day-night cycle?”

“Every living organism on the planet—from bacteria to fish to plants to humans—has a circadian rhythm, it's a fundamental property,” Zeitzer says. “But now with 24 hours of electric lighting and transcontinental travel, our biology is not set up to behave this way. We can adapt, but our bodies were not meant to do this.”

The concern is long-term dehabilitation. Potential high-risk groups such as flight attendants and shift workers, particularly nurses who work the second and third shifts their entire career, are the focus of specific studies to understand light's impact on the human biological clock at odd times on an ongoing basis. Although it is possible to train our biological systems to be at “peak” performance all the time, it would come at great expense as we would neutralize our circadian systems.

RESEARCH INTO APPLICATION At the Lighting Research Center (LRC) in Troy, New York, assistant professor Mariana Figueiro is investigating what color and type of light is more effective in coordinating with our circadian rhythms. “We want to understand light's impact on alertness at different times of day and how the retina converts light signals,” she explains. In 2007, the LRC received a $1.8 million grant from the National Institutes of Health (NIH) to develop a light meter that measures the 24-hour circadian light-dark cycle. According to a press release from the LRC, the wireless device, called a daysimeter, has “the capacity to communicate with the user in real-time to give immediate feedback regarding proper light exposure to promote a synchronized circadian rhythm.” The goal, according to Figueiro, is to convert these light-dark patterns into protocols that can be used in animal studies to enable researchers to start exploring certain diseases such as diabetes and obesity.

DESIGN IMPACTS The challenge then becomes how to translate research into applications. To date, the design of healthcare facilities has received great attention, to the point where hospital designs now incorporate more natural light into patient areas than before. Oberkircher points out that the dynamic quality of daylight as it changes in intensity, angle, and color often is forgotten by designers when considering light sources in a space. “We need to be more aware of the dynamics of the lighted environment,” he states.