Natural is often best, and that statement is also true when it comes to illuminating interiors. However, daylight must oftentimes be supplemented with electric light to meet code requirements and provide adequate lighting around the clock, particularly in environments in which people spend significant amounts of time, such as workplaces, schools, and healthcare and senior living facilities.
Newer editions of building codes factor energy conservation in their lighting specifications, but scientific studies have also connected quality of light to human health and well-being; that is, lighting needs to meet both the visual and non-visual needs of occupants. The relatively new concept of human-centric lighting encourages lighting designs that balance visual, emotional, and biological benefits, regardless of the source of the light.
What the Codes Say
Currently, building codes that prioritize energy efficiency place a premium on lighting power density (LPD) limits. These codes establish maximums, expressed in watts per square foot, that can be defined by space to space, whole building, or performance target.
For more than 35 years, ANSI/ASHRAE/Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings has been the benchmark for commercial building energy codes, and it is the basis for the International Energy Conservation Code (IECC). Many jurisdictions have adopted the IECC; the highly populated states of California and New York have even implemented more stringent requirements aimed at conserving a greater amount of energy.
Because lighting should both integrate with and enhance the overall building environment, architects often turn to experts—lighting designers, M/E/P engineers, and lighting manufacturers—to calculate appropriate, code-compliant lighting levels using sophisticated software packages, and to recommend fixtures. At the same time, lighting manufacturers are continually challenged to produce new luminaires that meet ever-evolving code requirements.
Health Concerns Tied to Electric Lighting
The benefits of daylighting to humans are paramount: Daylight can boost occupant productivity, provide comfort, and enhance circadian rhythms. However, natural light isn’t the only type of light that can affect human health. Electric light, which comprises visible light as well as the ultraviolet and infrared spectrums, can have an impact as well. For example, some LED lamps still exhibit flicker, a phenomenon that can cause eye strain, headaches, and even seizures.
Lighting’s effect on circadian rhythms has been a particular focus of recent medical research. Human beings have physically and mentally evolved to operate on a 24-hour schedule and are tuned to respond to natural light cues. Ideally, we are exposed to cooler lighting (with color temperatures between 5000K and 6500K) during the day to keep us alert, and warmer lighting (2700K or less) in the evening, which promote healthy sleep patterns. However, those who spend most of their days indoors, say, working, may have out-of-sync circadian rhythms, and that can lead to health issues.
“If your biological clock is out of sync with your watch, it’s like having jet lag all the time,” says Mariana Figueiro, director of the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute (RPI), where she is also a professor at RPI's School of Architecture. LRC researchers have tailored lighting interventions to promote circadian entrainment and minimize disruption. Short wavelength blue light, Figueiro notes, has a greater effect on circadian rhythms than longer wavelength warm or red light because it suppresses the natural production of melatonin—the hormone produced by the body at night to regulate sleep—and tricks the brain into remaining alert.
Metrics to Evaluate Electric Lighting
To quantify light’s effect on the human circadian system, the LRC developed a circadian stimulation (CS) metric to indicate the extent to which a given light source suppresses melatonin. The LRC’s website offers an online calculator that allows designers to input multiple factors, including light fixture specifications, and output CS values, among other lighting characteristics. Additionally, the Illuminating Engineering Society also provides many resources related to best practices for lighting design.
“Appropriate CS levels throughout the day result in better sleep and mood,” Figueiro says. She suggests using a tunable lighting system that transitions between cool and warmer light temperatures, within the ranges referenced above. “It is also important to specify the minimum amount of light needed for activating the circadian system,” she adds, noting that many of LRC’s field studies have revealed that light levels in the built environment are at or below these thresholds for proper activation.
Lighting Design Techniques Aimed at Occupant Well-being
Building codes set forth minimum guidelines, but “designers and practitioners need to understand how the limits are applied, what lighting can be exempted from compliance, and where there are allowances that can be applied for special purposes,” advises a guide from the U.S. Department of Energy.
Figueiro encourages architects to think beyond ceiling-mounted tunable lighting systems and instead create layers of light that illuminate both horizontal and vertical surfaces. For example, LED wall panels at eye level could emit blue light throughout the day—potentially replacing that 3 p.m. cup of coffee—and shift to red light later in the evening. However, if ceiling fixtures are the most viable choice, Figueiro suggests that the ratio of horizontal to vertical illuminance is at least 7 to 10, since light aimed at the cornea most effectively stimulates the circadian rhythm.
Another option is to create a “light oasis,” a designated area where occupants can retreat to benefit from therapeutic lighting. Exploring this concept last year at Salone del Mobile in Milan, San Francisco–based Studio O+A created “The Water Cooler” installation as part of a larger exhibition “A Joyful Sense at Work.” Studio O+A conceived areas for relaxation and recharge, including one space wrapped with soft seating with reclined backs against which people could rest while watching projections of water and bubbles on surfaces overhead.
If planned thoughtfully and carefully, lighting has the potential to be a design tool that alters the mood of a space. It can cultivate environments that range from energizing and engaging to calming and soothing. However, architects should note that electric lighting can do more than just help meet the required foot-candles on the ground or working surfaces as required by many codes. For example, uplighting is less efficient than downlighting, but it often contributes to a more comfortable atmosphere. To avoid glare, architects should also consider the reflective qualities of surface materials, or the light reflectance values for ceilings, walls, and furniture.
Finally, easily accessible user controls, from individual task lights to dimmers for overhead fixtures, can not only result in energy savings but also empower occupants and make them feel more invested in their environment. Having a sense of control, even on a seemingly small scale, makes most of us feel better instantly.