In Search of Healthy Lighting

Feb. 1, 2004
Laura Prestwood

Lighting needs to do more than support human vision.

FORUM | IDECIn Search of Healthy LightingCurrent lighting technologies support human vision, but in the future lighting technology needs to do more.By Laura Prestwood

Each day interior designers make decisions that impact the health, safety and welfare of the general public. How often is lighting considered as an integral element for achieving these goals? The concept of good lighting is changing because of recent research in the fields of neurobiology, photobiology, vision and lighting itself.

In November 2002 the Electric Power Research Institute, in conjunction with the Lighting Research Office, sponsored the 5th International Lighting Research Symposium in Orlando, FL. The three-day symposium featured emerging research in the area of light and human health. This research and subsequent findings have dramatically impacted the field of lighting design and our approach to lighting application. This essay is based on the seminar discussions and subsequent research findings, but by no means serves as an extensive overview for light and human health.

Recent findings, highlighted at the symposium, with regard to light and human health include the following:

  • light can alleviate seasonal depression;
  • light can increase the length and quality of sleep;
  • light can consolidate sleep/activity patterns in Alzheimer's Disease patients;
  • light can improve performance of night-shift workers;
  • light can improve weight gain in premature infants;
  • light activation of the circadian system is affected by a newly discovered photoreceptive mechanism in the eye;
  • light regulates melatonin, which has been shown to reduce breast cancer growth; and
  • light has direct impact on cortical brain activity.

Keynote speaker, Mark Rea, Ph.D., Lighting Research Center, Rensselaer Polytechnic Institute, posed the question "Are we
providing healthy lighting in our offices, schools and homes?" Rea also contended that good or healthy lighting cannot be
delivered until "researchers and practitioners begin to consider, measure, calculate and control the fundamental characteristics of light for the circadian system."

Much has been published with regard to circadian rhythms and light exposure in recent months. The word circadian comes from the roots circa, meaning approximately, and dies meaning day. The circadian clock is housed in the suprachiasmatic nucleus (SCN) found in the brain. In general, our circadian rhythms regulate basic body functions such as our sleep/wake patterns, hunger, body temperature and hormone production or suppression. Light received by the eye is used not only for vision, but also for regulating these body functions through the SCN, pituitary gland, pineal gland, adrenal gland and thyroid gland.

The research about the circadian system is ongoing, but there are several significant points. According to recent publications, what we know today about light and the circadian system is:

  • Light has been successfully used to treat Seasonal Affective Disorder (SAD).
  • Daily exposure to daylight is necessary to reset our biological time clocks. A simple 20-minute morning walk each day can reset the circadian clock and provide exposure to necessary blue wavelengths found in daylight.
  • Exposure to ultraviolet rays stimulates the production of Vitamin D.
  • For our health we need to spend time during the day in brightly lit interior environments. In the evening, conversely, we need to spend time in dimly lit environments with appropriate task lighting.
  • Sleep should occur in darkness. Light exposure at night will, for example, suppress melatonin (sleep hormone) secretion. Melatonin is currently believed to be the primary hormone associated with signaling all circadian photobiological functions.
  • Red, orange or amber wavelengths are less disruptive to normal sleep and circadian rhythms than blue wavelengths. Simply put, we should not turn on lights at night when we get up; if we must have nightlights, they should be red in color.

While extensive research has provided a solid foundation to support lighting standards which aid human vision, current research suggests that the criteria for appropriate lighting to support the circadian system is different than lighting for human vision. For all we are learning with respect to light and the circadian system, there are several key factors that are not known and are therefore the focus of current research. These significant components include the (1) quantity, (2) spectral composition, (3) spatial distribution, (4) timing, and (5) duration of light.

The following brief explanations serve to define the significant components listed above. Research in each area will provide the reader with a more comprehensive understanding of each category. Quantity refers to the light level measured in lux. Daylight for example can be measured between 2,000 to 10,000 lux on the ground while typical interior illumination may not exceed 1,000 lux on a work surface. Spectral composition refers to the particular wavelengths of the visual spectrum that stimulate the circadian system. As stated earlier, the short wavelengths of blue appear to be most stimulating. Spatial distribution refers to the irradiance measured at the eye. The specific composition of receptors in the human eye that appear to be most sensitive to the circadian system are located in the lower portion of the retina. This information may impact required horizontal versus vertical illumination levels as measured at the eye. Timing relates to core body temperature and when light exposure is received during the day or night while duration deals with the length of exposure and the subsequent impact to circadian regulation. Duration of light and frequency/pattern of exposure is directly related to phase shifts in the circadian cycle.

Light is critical to our health and productivity in the workplace or at home. As evident from the findings above, the type and amount of light to which we are exposed dramatically impacts how we work, play and rest. While our current lighting technologies are geared toward supporting human vision, future lighting technology will need to address the impact to the circadian system. As keynote speaker Rea has stated, our definition of "good lighting" must be re-examined.

Laura Prestwood is an assistant professor at Texas Christian University and teaches courses in interior design and lighting design within the curriculum and in conjunction with the TCU Center for Lighting Education. Readers interested in learning more about the symposium can purchase a copy of the proceedings by contacting the Lighting Research Office. For additional information, contact IDEC at (317) 328-4437 or

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