ASSIST evaluates outdoor lighting impact on human circadian system

June 28, 2010
Research reveals that outdoor lighting has little if any impact on human biological cycles in the face of worries of some advocacy groups about bluish short-wavelength light.

The Alliance for Solid-State Illumination and Technologies (ASSIST) has published a technical paper developed by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (RPI) that examines what if any effect outdoor lighting has on human circadian cycles. Advocacy groups such as the International Dark-Sky Association (IDA) have claimed that blue-spectrum wavelengths found in sources such as LED-based solid-state lighting (SSL) can disrupt circadian rhythms but the new research largely refutes that claim.

Last year, the IDA issued a statement proclaiming that bluish light can harm vision as well as impacting biological cycles. To test such a possibility, ASSIST studied four typical outdoor light sources including two cool-white LED luminaires.

The tests included an evaluation in a controlled laboratory environment as a reference, and in two typical streetlight scenarios that replicate typical distances from the source and viewing angles. The paper concludes that three of the four sources "would not meaningfully stimulate the human circadian system after one hour of exposure." A 6900K LED source that was tested could have a slight impact.

The tests relied on a model of human circadian phototransduction that was previously published by the LRC. The tests simulate a one-hour exposure to light relative to a 20-year-old person. The researchers calculated melatonin suppression that would occur based on the exposure with each source. Melatonin is a commonly accepted biological marker used in circadian rhythm study.

The study predicts that the 6900K source will provide 3-10% melatonin suppression. The suppression falls below a 15% threshold that might be more problematic. LRC director Mark Rea said, "Although stimulation of the circadian system is not necessarily synonymous with health risk, it is essential to determine if and to what degree light sources used outdoors at night might stimulate the circadian system. This study is a good start toward quantitatively understanding if outdoor lighting poses a concern.”

ASSIST is a collaboration of manufacturers, research institutions and organizations that is focused on indentifying and overcoming urdles facing solid-state lighting (SSL). ASSIST sponsors include Acuity Brands Lighting, Bridgelux, the China Solid State Lighting Alliance, Cree, Everlight Electronics, the Federal Aviation Administration, GE Lumination, the Industrial Technology Research Institute, LG Innotek, Lighting Science Group, Lite-On, NeoPac Lighting, the New York State Energy Research and Development Authority (NYSERDA), OSRAM, Permlight, Philips, Sharp Laboratories of America, Seoul Semiconductor, the United States Environmental Protection Agency, and WAC Lighting.

The LRC is a leading university-based research center devoted to lighting. LRC conducts research, demonstration, and educational activities on behalf of ASSIST.