Republication of Postings from the U.S. Department of Energy (DOE) Solid-State Lighting Program by Jim Brodrick, SSL Program Manager, U.S. Department of Energy

Among the many possibilities enabled by the advent of SSL is the use of light to trigger or suppress certain physiological responses of living things — from humans, to animals, to plants. SSL makes this possible because of its controllability in terms of on/off/dim, spectrum, and light distribution. But a much better understanding of the responses to light by humans, animals, and plants is needed in order to take full advantage of this intriguing potential.

That’s why DOE recently facilitated two roundtable meetings — one in April on animal responses to light, and one in July on human physiological responses to light. The roundtables featured experts in the respective fields (human or animal response to light), along with members of DOE’s SSL team and experts in LED lighting. The discussions highlighted what we know and what we don’t know, focusing on common research themes, research challenges, and paths forward toward a better understanding of human and animal responses to light.

The April roundtable, hosted by the Midwest Energy Efficiency Alliance in Chicago, focused on three fields of animal research: livestock productivity and wellbeing, wildlife and landscape ecology, and animal testing for human medical research. While each faces unique challenges, the attendees indicated that research should focus on determining what lighting spectrum, control protocol, distribution, and intensity are necessary for the desired benefit. This understanding would enable development of SSL products that increase animal wellbeing and the productivity of livestock operations, minimize wildlife and ecological impacts, and improve the effectiveness of human medical research.

The July roundtable meeting focused on human physiological responses to light. Participants identified four research themes: photoreceptive inputs and their responses, methods of circadian and neurophysiological regulation, human physiological responses to light, and product application hurdles. It was agreed that the researched effects of light on humans are critical for understanding what inputs could produce different nonvisual effects, and that much more research is necessary. Additionally, with the proper understanding of the specific effects of light on alertness and sleepiness, light could potentially act as a non-pharmaceutical tool to support a healthy circadian rhythm. And while existing research assures us that short periods of direct LED light exposure from almost all commercial products will not cause optical damage, additional work is needed to confirm that, for any kind of light source, there are no spectral power densities that can cause problems with prolonged exposure. The experts concluded that findings from controlled laboratory-scale studies need to be further evaluated under real-world conditions. Studies coordinated between physiologists and LED lighting experts would help clarify what happens when photoreceptors receive different inputs, and how light could best be applied to help control circadian and neurophysiological regulation and reduce the occurrence of light-influenced disorders. Ultimately, this will enable better metrics for describing physiological impacts of light and creating products that address these responses.

In addition, in May DOE participated in the 8th International Symposium on Light in Horticulture (LightSym 2016) at Michigan State University, in order to learn and to take part in the discussions. The use of LED lighting in horticulture is attracting considerable attention, since spectral, distribution, and instantaneous on/off/dim capabilities of LED lighting can be used to affect the size, color, nutritional content, and growth rate of vegetables, fruits, and flowers in greenhouses and vertical farms. The underlying efficiency improvements and cost reductions that have allowed LED lighting to gain adoption in general illumination are also expected to drive adoption in horticultural applications.

The physiological responses of plants, animals, and humans to light represent a complex interaction that requires dedicated research efforts. At the same time, the advent of SSL has enabled new levels of control over lighting that can be guided by better understanding of its nonvisual benefits. These new levels of control enhance the value of SSL in many applications that go beyond the static provision of light. This new added value can be applied to lighting that interacts with living things. However, a better understanding of the underlying responses to light is critical, as well as new metrics and criteria that can be used to drive product development and communicate the new values presented by LED technology.

The roundtable reports are available online.