Credit: Tang Yau Hoong

The design community’s interest in the role of human factors in lighting is growing. While technology may seem to drive our industry, designers are concerned with enhancing human experiences in the spaces they create—and with good reason. Lighting influences everything from human health, worker productivity, perception, safety, circadian rhythms, the aging eye, discomfort glare, and cognition.

It also affects how people experience architecture; lighting can help or hinder how they process the environments they encounter. Each time a person walks into a new setting, the brain is challenged with constructing a cognitive map—a mental representation of the key elements of the scene and their interrelationships—of its surroundings to use as the basis for how to act. Our sensory systems feed information derived from sights, sounds, and smells to the brain, which then compares the current cognitive map to scenes experienced in the past to see if any experiences stored in memory can help inform how to react and behave in this new setting.

To illustrate how environmental cues and attributes guide the construction of an internal cognitive map, which in turn guides how people interact with their surroundings, imagine standing at the entry to a new exhibition at your local museum. Directly ahead is the show’s headliner, an artifact accented with tracklighting to distinguish it from the dim surrounds. But you still don’t understand the layout of the exhibition. As you move farther inside, accent lighting draws your attention to a statue at the center of an open space to your right. You then notice that the room becomes a larger exhibition space, which extends deep into the building beyond the statue. Comfortable that you now understand the expected pathway through the exhibition, you return your attention to the entry display. And all of this happens in a matter of seconds.

Research into the cognitive map began decades ago, in fields such as environmental psychology, environmental behavior research, and man-environment research. Different researchers have addressed narrower aspects of the overall, broad topic. For example, John Brebner, a psychology professor at the University of Adelaide in South Australia, studied how people use information garnered from their past to extrapolate general principles embedded into their perceptions and how they apply those principles to new experiences in different settings.

Amos Rapoport, a retired architecture and urban planning professor at the University of Wisconsin-Milwaukee, has also written extensively about the cognitive goal of deriving meaning from environmental cues. People expect the environment to communicate meaning and rules, and to indicate appropriate behavior, Rapoport argues. Difficulty arises when the cues are either too subtle to be noticed, or when they are incomprehensible or contradictory to other indicators that are also present. Meanwhile, Boston College psychology professor James Russell proposes that the cerebral appraisal of environments occurs through the assessments of overall pleasantness, arousal level, and dominance in terms of the level of control a person believes they have in the setting.

But the most thorough development of ideas from this field of research comes from Stephen and Rachel Kaplan, a husband-and-wife research duo at the University of Michigan. The Kaplans propose that people spend considerable mental energy throughout their lives on two fundamental purposes: making sense of the settings they encounter and assessing opportunities for participating in those environments.

The ability to understand one’s conditions and the potential to become involved with the environs will influence an individual’s personal preferences. Whether it is an outdoor park, museum, retail store, office, living room, or waiting room, how a person reacts to their surroundings is based in large part on whether they are able to make sense of and interact with their environment. Lighting, therefore, can be critical to helping people understand a space and can dictate how engaging the space turns out to be.

Coherence and Complexity
Though their research focused on how people experience exterior settings, the Kaplans derived principles about personal engagement that designers and planners can use to enhance people’s experiences in any setting. While the Kaplans reference these principles throughout their decades of research (to the present day), Cognition and Environment was their classic text that established the framework (see “People and Prose,” below).

Though many visual characteristics factor into defining an environment’s setting and how people participate in it, the Kaplans identified two primary properties: coherence and complexity. As people construct their cognitive maps, they instinctively seek information on these important spatial qualities.

In a coherent scene, the boundaries of the spatial envelope are easily defined and connected, and surface intersections are clear. Any element highlighted through lighting should help the viewer establish this sense of coherence. When important spatial properties, objects, or surfaces are difficult to identify because of the lack of visual emphasis, coherence breaks down. It can also be hindered through careless design, such as an unintended scallop effect on a wall or column that is irrelevant to the architectural space and which can become a distraction.

At the other end of the spectrum, an oversimplified space with uniform light levels and no highlights or emphases can also lead to coherence. However, while this approach avoids the negative cues that break down coherence, it also results in a boring and insipid space. Simplicity may be safe, but to create engaging spaces, designers need to introduce adequate complexity and visual interest.

Complexity helps satisfy the basic human desire for stimulation and interaction with the environment. In architectural lighting, techniques such as accent lighting on artwork reinforce the idea of engaging people with their surrounds. In the earlier museum example, the added complexity of focused lighting on the statue invites the visitor to step closer for a more detailed look, thus strengthening the sense of involvement.

Seeing, Hearing, and Understanding
The principles of coherence and complexity are often synergistic. Architectural elements with integrated lighting, such as wall slots or coves, enhance coherence by defining spatial boundaries and injecting visual complexity. The practice of highlighting objects with accent lighting allows distant focal points to emerge and aids in wayfinding. Both techniques help a person understand a space while encouraging them to engage with their surrounds. For lighting designers, the challenge then is to find a balance between these principles. At some point, adding elements of complexity can lead to visual clutter and hinder coherence.

Beyond visual perception, the principles of coherence and complexity apply to a large number of applications and human experiences. Music appreciation relies, in part, on a proper balance between these principles. Daniel Levitin, who heads the Laboratory for Music Perception, Cognition, and Expertise at McGill University in Montreal, describes this balance in his book, This is Your Brain on Music. When a musical piece is very simple, he writes, people tend not to like it. When a composition becomes more complex, people respond more favorably. But when a piece becomes too complex, it can become incoherent and evoke a negative response.

Although Levitin does not use the term “coherence” in his writing, the underlying principle is the same: Adding complexity to a cognitive stimulus can build interest and increases people’s partiality to an extent. When complexity reaches the point of diminishing coherence, the partiality disappears.

The Future of Lighting
As the lighting industry continues to focus on the proliferation of solid-state lighting, accompanied by ever-lower power allowances, nuanced discussions of human factors appear to have been lost in the shuffle. Overlooking these topics could have unintended consequences. Attempting to satisfy reduced power budgets using directional sources, such as LEDs, in systems designed only to satisfy task-plane illuminance levels could result in projects that fail to help the user understand the space or provide the complexity to make the setting pleasant. Also, the idea that eliminating accent lighting, wall-slot lighting, wall sconces, and covelighting might be the only way to meet future energy codes is a disturbing one, since these lighting strategies help designers create coherent spaces with suitable complexity. If small, bright, discrete light sources dominate the visual scenes of the future, designers will struggle to satisfy the design criteria without creating visual noise.

But what if luminaires, regardless of their source, were designed with human factors in mind? Technological developments have led to small-scale, highly efficient luminaires that can define spatial boundaries and highlight key objects at lower power levels. Several manufacturers have recently introduced new and smaller LED cove, wall slot, and wallgrazing products that add coherence and complexity at low wattages. LED and OLED sources also provide opportunities for innovative form factors. To date, those form factors are primarily used for decorative lighting, but perhaps they will inspire new ideas for architecturally integrating lighting equipment to boost coherence. Meanwhile, the combination of solid-state sources and controls opens doors for tunable systems that empower designers to create dynamic, visual, and engaging environments.

These new technologies are critical to the lighting industry’s future. If applied thoughtfully, they can also empower manufacturers and designers to create lighting solutions that fully address topics of concern in human factors, such as those associated with circadian health, an aging population, glare control, workplace productivity, and the need to comprehend and enjoy the environs in which we live, work, shop, and play. One of the Kaplans’ more recent books is titled With People in Mind. This simple phrase provides a concise call-to-action for the lighting industry as we move forward.

Robert Davis is a senior staff lighting engineer at the Pacific Northwest National Laboratory (PNNL) and holds a M.S. degree in architectural engineering and a Ph.D. in cognitive psychology. This article expresses his personal views and not those of PNNL or the U.S. Department of Energy.

People and Prose
Human factors are a complex area of research, and lighting is but one part of this very nuanced subject matter. Below is an introductory bibliography to the topic. 

Lighting Books
Architectural Lighting Design, 3rd Edition, by Gary Steffy, John Wiley & Sons, 2008. Chapter 7: Psychological and physiological factors.
Human Factors in Lighting: 2nd Edition, by Peter Boyce, Taylor and Francis, 2003. Chapter 6: Lighting and the perception of spaces and objects.
Light: The Shape of Space, by Lou Michel, Van Nostrand Reinhold, 1996. Chapter 11: Lighting the spatial envelope.
Perception and Lighting as Formgivers for Architecture, by William M. C. Lam, McGraw-Hill, 1977. Chapter 3: The process of visual perception.

Non-lighting Books
Healing Spaces: The Science of Place and Well-Being, by Esther M. Sternberg, M.D., Harvard University Press, 2009.
This is Your Brain on Music, by Daniel J. Levitin, Plume, 2007.
Cognition and Environment: Functioning in an Uncertain World, by Stephen and Rachel Kaplan, Praeger Publishers, 1982.
An Approach to Environmental Psychology, by Albert Mehrabian and James Russell, MIT Press, 1974.