By now even the most isolated consumer has at least heard of LED lighting. LED replacement bulbs are available in any hardware store larger than a closet. The case for the economics and quality of solid-state lighting has been won. Now the industry can concentrate on bringing true value to LED lighting. That value will not come in the form of lower energy use; it will come in the generation of light that enhances the human experience.

That means influencing some aspect of human comfort, health, or behavior by producing and modifying light’s intensity, spatial and angular distribution, spectral content, and possibly other characteristics. Before LEDs we had only limited control over the characteristics of light. Now we have nearly infinite degrees of control. With this control the question becomes: What is ideal lighting, and how can we produce it?

Schoolchildren in LED-lit classroom.

Philips LED lighting offers teachers the option of four pre-set lighting scenarios, ‘Normal’, ‘Energy’, ‘Focus’ or ‘Calm’. There’s a positive response, but what does it mean? Courtesy of Philips Lighting.

Are we ready to answer that? The just-completed Strategies in Light Conference in Las Vegas featured a workshop led by a truly distinguished panel of experts claiming that human centric lighting is ready now. The tenor and content of the discussion might be summarized by a slightly different title. Perhaps something like, “Technology is Ready to Start Investigating the Desired Qualities of Human-Centric Lighting.”

The argument put forward by the presenters is that they are already proceeding with human-centric lighting projects designed to optimize or improve some aspect of human behavior. Stan Walerczyk introduced the new solid-state lighting at the Seattle Mariners’ stadium — the first Major League Baseball stadium to make the switch — which includes (in the home team locker room only) features to tweak circadian rhythm for optimum alertness at gametime. Doug Steel talked about the growing body of knowledge linking various health conditions with light exposure — and the corollary that light exposure can potentially improve health outcomes. Professor Robert Karlicek described methods for integrating “non-invasive” sensors into lighting systems to produce light optimized for a given activity — hands-free because the sensor’s system autonomously categorizes the human activity. Mike Lambert described some human-centric lighting pilot projects in schools, including a school for autistic children.

The message is that light is already being used in innovative ways to influence human health, behavior, and comfort.

The Big Questions for Human-Centric Lighting

But some big questions remain. Bob Karlicek summarized the situation with a single statement: “We really don’t know what we don’t know yet about how lighting will influence how people learn and work.”

We don’t even really have a grasp of the most basic question:
In what ways do the visual and non-visual light receptors influence human behavior, mood, and health? It’s likely to be a very complex answer with primitive roots. That is, the intrinsically photosensitive retinal ganglion cells (ipRGCs) are very highly conserved, in biological terms. That means they appear even in “primitive” organisms only distantly related to humans, which points to a)their early origin and b)their importance to survival. That early illumination response had nothing to do with the human brain, as it was around far before there were any humans (or, for that matter, any brains). So there are going to be some very basic biochemical responses to light that are far beyond our conscious (or even unconscious) control. On the other hand, the human brain does a really good job of processing and manipulating sensory response. Basically, we can convince ourselves we feel one way when our body is telling us we truly feel something completely different. And that’s even before we introduce “thinking,” which makes everything more complicated. Thus, the complex answer with primitive roots.

Light and the brain.

Light influences the biochemistry of the brain, endocrine systems, metabolic processes, and — well, who knows where it ends? Courtesy of Nat’l Institute of General Medical Sciences.

That raises the next logical question:
How do we go about finding the answer to the previous question? One answer, proposed by Doug Steel at the SIL workshop, is to create environments where users get to choose their own lighting characteristics and then simply monitor what they do. He believes there is a natural tendency for people to drift away from their initial preferences — what they believe they like — to lighting that maximizes whatever it is they’re trying to optimize. If engineers partner with clinical professionals (many of whom are being dropped by pharmaceutical companies) then he believes these types of studies will identify (or at least illuminate ) the influence of light on human activity. On the other hand…there are so many confounding factors that the mechanisms might be hidden beneath layers of competing biochemical, emotional, and cognitive mechanisms. Professor George Brainard emphasized that point, reminding the panelists that there’s a well-developed successful path for performing this sort of research, progressing from animal through clinical studies. Although I don’t recall anyone explicitly stating this, the panelists’ consensus seemed to be that a)there are already companies out there claiming either specific or nebulous health effects of their particular lighting system, and b)traditional scientific discovery will take too long. So we should do what we can to provide at least some sort of scientific investigation into the effects of lighting, and we should do it right now.

Which brings up the final question, at least for this already long post:
What makes good lighting? In an elementary school classroom is the good lighting that which maximizes student performance or that which minimizes behavioral problems? In the work environment, is it that which maximizes worker productivity or worker comfort? If lighting makes me feel keyed up, as if I’ve been physically active, am I likely to eat more, even though I’ve been sedentary? Is lighting that makes me happy better than lighting that makes me more alert? And, distinct from those types of questions, there is the layer of light and health. You can imagine a scenario where I may feel good and work hard under certain levels of illumination, but that ends up triggering some photosensitive biochemical pathway that begins tumor growth.

My concern is that human studies right now will be almost necessarily one- or two-dimensional: looking at the effect of light on one or two aspects of human comfort, health, behavior, or activity. It’s likely that the complex structure of the human brain is reactive to illumination in many, perhaps contradictory, ways and if we really want answers we’re going to need to take as comprehensive an approach as possible.

The Human Centric Lighting Society is working on these sorts of questions, and you should take a look at their site if you want to get up to speed.