Researchers present circadian metrics and health impact of LED light at HCL conference

The second LEDs Magazine Lighting for Health and Wellbeing conference included a stellar roster of researchers and human-centric lighting experts, writes Maury Wright, and some of the more interesting talks focused on characterizing lighting for health and the direct positive and negative impacts of artificial light on health.


Author- Maury Wright

Sep 12th, 2018



Researchers present circadian lighting metrics and health impact of LED light at human-centric lighting conference

The second LEDs Magazine Lighting for Health and Wellbeing conference included a stellar roster of researchers and human-centric lighting experts, writes MAURY WRIGHT, and some of the more interesting talks focused on characterizing lighting for health and the direct positive and negative impacts of artificial light on health.


LEDs Magazine held its second Lighting for Health and Wellbeing Conference on July 18 in Newport Beach, CA, and the attendees got to hear from the top experts in human-centric lighting (HCL; Fig. 1). Many of the talks focused on the influence of lighting on non-visual systems and the circadian impact of lighting, although the program also included coverage of LED lighting as a way to reduce the occurrence of myopia (watch for an upcoming feature article), continuous disinfection through lighting, and lighting for health in the built environment. Perhaps the most compelling subjects of the day focused on characterizing lighting for health and understanding the direct impacts of light on health. We will focus on several of those presentations here.



FIG. 1. Conference attendees immersed themselves in topics from metrics to circadian impact to applying light for disinfection as well as therapeutic effects.

Mariana Figueiro, PhD, director of the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, opened the day delivering the Keynote Presentation. She posed the question, “What does light affect?” And she showed the diagram in Fig. 2, indicating an impact on visual and non-visual systems in addition to the psychological system.



FIG. 2. Visual, non-visual, and psychological systems are all impacted in different ways by lighting.

Figueiro said the systems on the chart “may be a small part, but it’s the part we know best.” Light could impact far more systems than are known today. “Even within these systems, I think lighting has different characteristics and impacts these systems differently,” said Figueiro.


The point is that it’s very complex and not fully understood at this point — a point echoed by many other speakers on the day. “But I don’t think we should just throw our hands up and say, ‘Oh my god, I can’t do anything,’” said Figueiro. She would go on to describe some steps that she urged practitioners to take now.


Psychological effects


Figueiro quickly moved into the perception of psychological effects on a person and focused in on red light. She said researchers at the LRC had noticed that red had an alerting effect on people. But the researchers assumed they were mistaken, because conventional wisdom holds that blue-rich light drives alertness. “That’s one thing I want you to remember from this talk,” said Figueiro. “It’s not just about blue.”


She referenced the work of Andrew Elliot, psychology professor at the University of Rochester, who has said that red is a danger cue for humans and it triggers a fight-or-flight reaction in people. Research has even shown that humans judge a person wearing a red shirt as being angrier than others wearing, say, blue or white.


Figueiro said the LRC has been looking more at the non-visual physiological effects of light rich with red energy. She said the research shows that red light during the post-lunch dip, or in the middle of the night, can improve alertness and reduce reaction time.


Circadian Stimulus


Next, Figueiro began to discuss the LRC’s work on a spectral sensitivity function called Circadian Light or CLA that further leads to the Circadian Stimulus (CS) metric. She said most current thinking on physiological response is that it’s not just melanopsin and the intrinsically photoreceptive retinal ganglion cells (ipRGCs) of the non-visual system that impact physiology. The visual-centric rods and cones play a role as well, although researchers are still working to understand the interaction. At the Lighting for Health and Wellbeing Conference in 2017, Jamie Zeitzer of Stanford University suggested that the visual system may provide some type of gain-control function.


Figueiro’s point, however, is that another popular metric, Equivalent Melanopic Lux (EML), is really tied specifically to the ipRGCs. EML does not account for any impact of the rods and cones. The CLA function has peak sensitivity around 460 nm. Figueiro explained that the model changes based on the spectral power distribution (SPD) and the amount of light, and the LRC has defined a straightforward way to calculate CLA.


Still, CLA alone is not enough for an accurate characterization of the impact of light on a person because Figueiro said it’s not just about spectrum, amount matters also. She said a CLA or EML measure alone would not be easy to evaluate as to threshold of impact or saturation of the physiological system. So the LRC developed the transfer function that uses CLA to derive CS, which characterizes the response by the circadian system.


Limitation of metrics


Figueiro warned of some limitations of using CS and also explained some subtle details of applying it. The work thus far is based on one-hour exposure time to a specific light source. And it only considers melatonin suppression as a measure. But duration matters, and light impacts many physiological systems beyond melatonin level. And she stressed that applying CS requires a strict measure of light at the eye. A measure of horizontal illuminance would not deliver accurate results. Measuring at the eye takes into account the full beam distribution and reflections from surfaces in a space. The LRC has recommendations on CS levels for different times of day and tasks at hand.


Referring to tests based on the CS metric, Figueiro offered some of her conclusions as to what we know. She said light has a direct or acute impact on people and that it doesn’t have to be blue light that is used to increase alertness. For example, you can use red light at night to achieve the impact without changing a person’s circadian phase. With different SPD, you may need to increase the light level to achieve the same CS. Meanwhile, work continues on the impact of duration, but Figueiro said it appears duration beyond two hours seems to have a much lower impact.


Returning to the theme that we don’t know everything, but we should do something, Figueiro concluded, “I think that if we over-design... If we just get bright light during the day, because right now we are under dim light constantly. If we just increase a little bit more… I think we can start making a change in the builtenvironment.”


Characterizing circadian potency


Also focused on the topic of metrics was Martin-Moore-Ede, MD and PhD, founder of Circadian Light and the professor who led the team that discovered the SCN (the body’s master pacemaker) back in 1980 at Harvard. Moore-Ede’s presentation was entitled “Circadian potency: Circadian spectral sensitivity to white light in the workplace.” He began by asking the question, “What is the spectral sensitivity that we need to work with?” He noted that the $120 billion lighting industry needs to know this, and lighting designers and specifiers also need to know.