Light and Human Health

03/01/2004 |

Research Sparks Questions About Roles of Interior Lighting

New research makes it clear: We do not know nearly as much as we thought we did about light and lighting. In fact, we have so much to learn – and to turn into common practice – that the criteria we use to design indoor lighting could be altered drastically over the next few years.

Perhaps the most important of all developments is a newly discovered photoreceptive sensory system, housed in the eye, but not involved in vision. This discovery is spurring exploration into the relationships between the visual, nonvisual photoreceptive,  and circadian (biological rhythm) systems in humans; or, stated simply, into the topic of light and health.

While light is already used in a number of therapeutic applications, such as the treatment of seasonal affective disorder (SAD), certain sleep problems, depression, and jet lag, the new research may hold the key to an unprecedented leap forward in what benefits lighting might be expected to provide for occupants of buildings in the future.

The new discoveries have taken a long time to tease out. While three centuries of research have been dedicated to the visual system and we have had electric lighting for 120 years, only 40 years have passed since the world recognized that the circadian system is sensitive to light and the environment. The past 20 years have been devoted to its effect in humans, but the real breakthrough discovery – identifying exactly how the eye detects light in nonvisual ways for circadian regulation – was first published in 2002.

Our knowledge of vision is well-established. Light comes into the eye; complex signals are sent from the rods (night vision) and cones (daytime vision) to the thalamus, and then to the visual cortex. But in the case of the eye’s nonvisual circadian sensory system, a separate nerve pathway leads from a group of ganglion cells on the retina into nonvisual parts of the brain, such as the hypothalamus, for circadian regulation; the control of hormones and metabolism; and to influence human performance, health, and well-being. Intensive research is under way to learn how these ganglion cells detect light, how much light is needed for them to respond, and their wavelength (color) sensitivity. Next will come the complicated task of figuring out how to apply the knowledge to practical lighting systems – a task that is already under way.

What It Means to the Industry

In December 2003, the Silver Spring, MD-based National Lighting Bureau (NLB) convened a group of professionals (see Roundtable Participants, below) to share information about the new research exclusively for Buildings magazine. In addition to the NLB, hosts for the roundtable included the National Electrical Manufacturers Association (NEMA), which lent a portion of its Rosslyn, VA-based headquarters for the event, and the Lighting Research Office of the Electric Power Research Institute (EPRI), headquartered in Palo Alto, CA. Many of the participants have been actively involved in either research and/or gathering information about the correlation between light and human health; the recent discovery has elevated interest and a desire to promote awareness.

Roundtable participant Dr. George C. Brainard, Department of Neurology, Jefferson Medical College at Thomas Jefferson University, Philadelphia, opened the enthusiastic session with an important caution: “It’s important to know about this discovery, but it’s just as important to understand that this research is only in its infancy. You don’t want to start making fundamental changes until you have the full complement of facts. The prudent approach now is to foster collaboration between the scientific, biomedical, lighting, and architectural communities.” Brainard suggests that building professionals can play a critical role in guiding applied research on architectural applications that optimize lighting for health and well-being. He adds, “Science has to go to a collaboration. Without input from engineers, designers, and facilities people who understand the real-world and financial issues, it’s going to be hard to transform the new biological discoveries into something practical.”

Terry McGowan of EPRI’s Lighting Research Office concurs with this assessment, noting, “For the last 30 years in lighting, the primary concern has been energy: How do we get our lighting for the least amount of power so we save money and energy in buildings? That’s fine; but the result has been to shift the focus of lighting from human beings to power meters. If buildings – and lighting – are for people … to get work done in a healthy and productive environment, how should we now be designing and using lighting? The new research indicates that lighting has a role to play that goes beyond the traditional role of vision.”

Bottom-line Impacts

Light is part of the productivity equation. People need an adequate amount of comfortable light to see efficiently and accurately, and to minimize fatigue. Research work from the late 1800s through the 1960s told us how much light of what quality was required. Recommendations from organizations such as the Illuminating Engineering Society of North America (IESNA) and the National Lighting Bureau have made good lighting common practice and helped calculate the value of light. It’s easy to show that the cost of lighting is a tiny part of what it costs to get the job done – typically less than one percent. As NLB Chairman Jim Yorgey puts it, “The value of benefits like improved productivity, fewer errors, and lower insurance rates [due to improved safety] dwarf the amount of money that can be saved from energy savings alone. Now, we are just beginning to see that the health benefits of proper lighting could dwarf all the others put together.”

Biological Effects of Light

Although researchers have long known that light has biological effects – which is why very targeted light stimuli have been used to counteract certain clinical problems, like winter depression or SAD – they did not know the basis of these effects. A better understanding of these basics may now lead to the routine use of light stimuli in non-clinical applications, such as when the circadian system of a human being is disrupted via shift work. Consider this: According to Brainard, 20 percent of the U.S. population is engaged in shift work, and long-term shift work has now been linked to a variety of health issues, including being a suspected risk factor in the development of certain cancers.

Other diseases, including diabetes, also appear to have links to the circadian system and, therefore, to light, so the research bears watching, acknowledge the roundtable participants. If the links can be confirmed, then  managing light in a facility for the optimum health and well-being of building occupants becomes critical. Some researchers talk about “light deprivation” – situations where large groups of people go to work or school in the dark, sit in low-level lighted environments all day, and return home in the dark. They may not get a “dose” of normal outdoor illumination for days.

But dark may be as important as light from a circadian standpoint. We know that light stimuli, as well as darkness – the lack of light – helps re-adapt shift workers to avoid some of the health consequences associated with shift work. We need to know how and why the body reacts to the presence and absence of light. In that regard, roundtable participants agree: If one acknowledges that light is an active stimulus for beneficial therapeutic effects, one must acknowledge there may be potential side effects or negative consequences of light and darkness at inappropriate times.

The Benefits of UV

With rickets reappearing as a childhood disease and an aging population prone to osteoporosis, ultra-violet light – and the benefits of the Vitamin D production it stimulates – is once again being discussed in lighting circles. In fact, say roundtable participants, a 10- to 15-minute walk outdoors with hands and face exposed is sufficient to derive an adequate amount of Vitamin D synthesis, depending upon the location and time of year.    

“There are now agreed-upon safety standards that have been developed by the IESNA to protect people from excessive exposure to UV, and the UV that we’re generally most concerned about is referred to as ‘UV-B radiation,’ which is very intense at mid-day and almost non-measurable when the sun is low in the sky,” says Dr. David Sliney, U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD. “That same UV-B is what stimulates the production of Vitamin D. Therefore, you need some; but not too much. There have been a number of studies, such as the one done in a Veteran’s Administration home, where people were placed in rooms where they received a little extra UV from special fluorescent lamps. Apparently, it did reduce the problem of osteoporosis. So, the challenge will be to come up with a more workable solution in our normal working environments.” As one roundtable participant observed, however, “If we can identify the amount and quality of light that’s best, and the optimum exposure, it’s far easier to provide it with electric illumination and control systems than it is to try to match ideal conditions outdoors, especially in parts of the country where latitude or weather limits UV from the sky for much of the year.”

Sliney also notes that there are public health implications in using a very short-wave type of UV, known as UV-C, which reduces airborne bio-aerosols and subsequent infections from, for example, influenza. “The health community is interested in how we apply that ultraviolet [germicidal UV] safely,” he adds.

One approach, literally available now, is to place a UV-C system in air ducts. People face zero risk from such UV exposure, and owners can achieve a fast payback in terms of reduced worker absenteeism and fewer sick days per year. “There’s new data because of a large ongoing study managed out of St. Vincent’s Hospital in New York City, which uses germicidal UV units installed in buildings such as homeless shelters,” notes McGowan. “The new data are telling us how much UV is needed, what kind of equipment to use, and how to distribute that UV in buildings safely.” The data indicate that there are benefits wherever people inhabit enclosed spaces. Airplanes, with their notorious recycled air, are also a potential application.

Steering the Industry Ahead

In a few years, say roundtable participants, we’ll have enough information to know how much lighting exposure we need; what time of day it has to occur; the intensity required in order to stimulate positive responses; and, conversely, how and when to limit light at night. “Right now,” explains Naomi Miller, Naomi Miller Lighting Design, Troy, NY, “we still don’t have enough information for comprehensive recommendations, so we’re taking a cautious approach.

“But let’s first start doing some common-sense things that aren’t expensive and which are simple to accomplish – some of which involve behavior modification. We need to tell people they need to go outside more during the day; they need to be exposed to brighter light during the day; they need to get their UV dose. We can’t decide to change light levels indoors at this point because we don’t know the dose characteristics required for general populations.

“What I do think is going to be an important change is to stress … that we need to have more daylighting, because we know more daylighting is healthy for us. It naturally provides the right spectrum. It provides high light levels. One thing we can do right now to make environments much more pleasant is to introduce more well-designed daylighting into buildings.”

Both Sliney and Brainard agree. Brainard points out: “There are now six published studies on animals and humans that show the circadian and neuroendocrine systems have their highest sensitivity to light in the blue portion of the visible spectrum – which is naturally abundant in daylight.”

Other roundtable participants also agree on what steps can be taken now. “There are things we can do; things we have responsibilities to do as manufacturers or designers or building owners. And there are lots of things we can do in terms of research to apply what’s coming out of the medical community to practical building technology,” says McGowan.

“It’s not difficult to imagine,” says Yorgey, “that in just a few years from now workers will demand ‘healthy lighting.’ Everything could change.”

Buildings readers, take note: Keep on top of this evolving issue by accessing the leaders in the lighting field – researchers, designers, manufacturers, associations, and others. Do your part in asking good questions; link up with experts who have honest, up-to-date information; and closely follow the rigorous research under way.

And, beware, too, this is a subject where “magic” light bulbs, like “patent medicines,” are common. Make sure you’re talking to the experts.

Linda K. Monroe ( is editorial director at Buildings magazine.

Healthy Lighting –
Some Easy Common-sense Approaches


  • Take a 20-minute walk outside in the morning (to get a blast of light for circadian rhythm reset). Wearing sunglasses or a brimmed hat on very bright days is okay.
  • On winter days in northern climates (roughly latitude 35 degrees and above), take another 15-minute walk outside between 10:00 a.m. and 2:00 p.m. Expose your face and hands to the light (there’s minimal UV-B; but take advantage of what there is for Vitamin D synthesis). Wearing sunglasses or a brimmed hat is okay. If you have dark skin or if you are wearing sunscreen or make-up, take a longer walk.
  • Consider taking Calcium and Vitamin D supplements (consult your doctor, of course), especially if you don’t eat cereals or dairy products with added Vitamin D.
  • Spend time in brightly lit spaces during the day, especially spaces with windows, skylights, courtyards, etc. These should be designed to control glare for users. Just sitting next to a (non-tinted) window facing open sky will expose you to substantial illumination even on a gloomy day.
  • Spend time in dimly lit spaces during the evening as the body prepares for sleep. Task lighting for reading or doing household work is okay, as long as the whole room isn’t bright.
  • Sleep in the dark. Use black-out shades if you live in an area with streetlights or light from neighbors or businesses pouring in the bedroom windows. (Eye shades work, too, and they’re less expensive than black-out shades for windows.)
  • Don’t use lights during the night unless they’re very dim. Red, orange, or amber lights affect the circadian system less than white or blue.




Roundtable Participants


Dr. George C. Brainard, Department of Neurology, Jefferson Medical College,

Thomas Jefferson University, Philadelphia, PA.

Cheryl English, Acuity Brands, Conyers, GA.

Naomi Miller, Naomi Miller Lighting Design, Troy, NY.

Terry McGowan, Lighting Research Office, Electric Power Research Institute (EPRI)


Dr. David Sliney, U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD.

Scott Watson, International Association of Lighting Designers (IALD), Chicago (

David Weems, GSA, Washington, D.C.

James M. “Jim” Yorgey, PE, LC , Lutron Electronics Co. Inc., Coopersburg, PA.

Roundtable Moderators

Linda K. Monroe, Editorial Director, Buildings magazine, Cedar Rapids, IA.

Regina Raiford Babcock, Senior Editor, Buildings magazine, Chester, PA.

Roundtable Observers

Douglas Baillie, Acuity Brands, Conyers, GA.

Kyle Pitsor, National Electrical Manufacturers Association (NEMA), Rosslyn, VA (

John Bachner, National Lighting Bureau (NLB), Silver Spring, MD (

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