The green design—good for the environment in that it makes buildings more sustainable—can be bad for lighting, as designers are incentivized to chase points that may require sacrifices to design. For lighting, it can be especially risky. Lighting power allowances in energy codes regulating new buildings have steadily declined over the last decade, enabled by advances in technology. Green rating systems, such as the Leadership in Energy and Environmental Design (LEED), are based on exceeding code, which may come out of design. It turns out saving energy is easy, but saving energy while achieving good lighting quality is hard. The problem is that energy-efficient lighting does not necessarily make effective lighting.
Part of the challenge stems from traditional lighting design’s focus on providing sufficient lighting levels on the horizontal task plane. In a corridor, it may be the floor or, in a classroom, the tops of the desks. In trying to squeeze every last watt out of the lighting system, these light levels may be pushed very low with a direct lighting system; the result may be highly energy-efficient but a gloomy atmosphere that does not serve architecture or people.
The solution may be wall lighting. Placing light on walls, considered best practice in contemporary lighting design, can produce two significant benefits. First, it defines the spatial form, making the area appear brighter and more expansive, while focusing attention on people and architecture. Second, when combined with high-reflectance surfaces, it produces useful inter-reflections that can enhance light levels and visual comfort.
Before discussing these solutions in detail, this article describes popular wall lighting techniques.
General lighting may include recessed general lighting placed close enough to room edges to illuminate the upper walls and mitigate the “cave” effect. Another option is volumetric-type recessed lighting, which is designed to distribute light on upper walls. And a third option is pendant-mounted indirect lighting (see Figure 1), which places light on the ceiling and walls, with visual emphasis on the ceiling as the brightest plane in the spatial envelope. While these options may be sufficient for some spaces, it may be desirable to employ dedicated wall lighting for others.
A basic lighting technique, wall washing involves placing ceiling lighting fixtures 2 to 3 feet from the wall and aimed at the wall at a wide angle, which results in a smooth wash of light from top to bottom. Because of the wide angle, small imperfections in the surface, such as tiny nicks and bumps, are washed out, making it visually flat. For large walls, linear lighting sources, such as fluorescent, are effective.
Because of the inverse square law, the fixture-mounting height would be limited to 8 to 9 feet. From the ceiling to about 2 feet down receives 80 percent of the light, while the middle to the lower wall receives 50 percent, and the area near the floor receives 20 percent. The floor area is typically obscured, so people are generally focused on the bright upper wall.
Another basic lighting technique, wall grazing, involves placing the lighting fixtures closer to the wall, resulting in a narrower angle, which in turn produces shadows that reveal texture. By moving the fixture closer or farther from the wall, the angle of light can be adjusted to make shadowing more or less pronounced and, thereby, achieve different grazing effects. Linear sources can be used, but point sources are generally preferred for strong grazing. Light-emitting diodes (LEDs) have great potential as an efficient grazing source.
Because grazing reveals texture and is visually arresting, it should be used with surfaces that are worth looking at and do not contain imperfections that we otherwise wish to hide. In the case of wall washing, the lighting reveals the spatial form as a luminous backdrop to people and objects. In the case of wall grazing, the wall itself is the focus of attention. As a result, grazing is typically used as accent lighting to beautify strongly textured surfaces, such as natural stone and brick, as well as artwork, such as carvings.
A grazing wash combines some of the advantages of wall washing and wall grazing (see Figure 1). This technique involves mounting linear sources in a continuous run around the edge of the ceiling (wall/slot lighting). The lighting equipment can be concealed, while the bright wash of light at the edge of the ceiling articulates that plane, resulting in a visually interesting “floating ceiling” effect. While the angle of light is narrow enough to render interesting architectural details, grazing wash is generally used similarly to wall washing—that is, to reveal the space’s dominant boundaries and produce inter-reflections.
Humans respond to light physiologically and psychologically. To understand the benefits of wall lighting, we must begin with the basic premise that brightness focuses attention. The human eye is naturally drawn to areas of brightness and brightness contrasts in the field of view. Contrast is even more important than brightness, which is why lighting designers consider darkness a very important tool in designing with light.
This basic premise is rooted in our scientific understanding of phototropism, the tendency of humans, animals and plants to seek light. People will reflexively orient themselves to squarely face sources of high brightness and strong brightness contrasts, as long as those sources are not uncomfortably glaring.
In the 1970s, Dr. John Flynn conducted experiments on people’s subjective responses to different lighting conditions. In one study, participants entered a cafeteria and were observed to have a preference to face the entrance. After wall lighting was added, participants entering the cafeteria changed their orientation and showed a preference to face the bright walls.
In another study by Taylor and Sucov in 1974, participants entered a room through a curtained entrance and read instructions on a room divider telling them to go to the other side and complete a task as part of a study of consumer product lighting. Unaware of the true intent of the study, they entered the room by choosing to go either left or right to get past the room divider. When both paths were lighted equally, seven out of 10 participants went to the right. When the path to the left received a higher light level, three out of four went to the left. Light not only focuses attention. It can help with wayfinding.
Benefits of wall lighting
Given this knowledge, it is a simple case to make that placing light on walls accomplishes two things. It highlights the spatial form, providing a pleasing luminous backdrop to people, objects and activities in the space, which is important for work spaces—while avoiding the gloomy “cave” effect exhibited by some direct lighting installations. And it places visual emphasis on vertical surfaces instead of horizontal surfaces, resulting in an emphasis on people and architecture, which is important for public spaces.
We have demonstrated that people are physically drawn to brightness and that brightness can be used to direct attention in walls and vertical surfaces in a space. But it is also true that people respond to patterns of brightness in a space psychologically, too.
This brings us back to Flynn’s research, which can be used to predict how people will respond to different lighting arrangements based on horizontal (overhead) versus vertical (perimeter) emphasis, uniform versus nonuniform distribution, bright versus dim light levels, and visually warm versus cool color tones (see Figure 2 for an illustration of these effects).
Fig. 2: Flynn’s research indicated that people form subjective impressions of built environments independently of the architectural context, categorizing them in terms of overall central or perimeter emphasis of the lighting. Shown here are eight renderings of a room, developed based on Flynn’s studies, with central, perimeter and combined lighting, bright illumination as a constant (compared to dim), and both uniform and nonuniform lighting patterns on surfaces. One can see at a glance how different lighting configurations produce different appearances of the space with different resulting subjective impressions.
In a series of simple experiments, people were exposed to different lighted spaces and asked to rate their subjective impressions on a scale between “pleasant” versus “unpleasant,” “spacious” versus “confined,” “relaxed” versus “tense,” and “visually clear” versus “hazy.”
Flynn found that brightness on walls tends to produce impressions of spaces as being “pleasant,” as people like light on walls. He also found that wall lighting can contribute to impressions of a space being “public,” “spacious,” “tense,” “open for business” or “businesslike,” and “visually clear,” particularly when light distribution is uniform.
Besides directing attention and influencing aesthetic judgment of a space, wall lighting can also contribute to visual clarity and comfort.
One of the most beneficial applications of wall lighting in applications with sustained, demanding visual tasks is to turn walls into area lighting sources, producing inter-reflections that can increase light levels, uniformity and visibility, while reducing shadows and strong contrasts. Increasing uniformity reinforces impressions of spaciousness, alertness and visual clarity. Increasing distribution on vertical surfaces increases their visibility, while improving facial recognition—which can aid face-to-face communication—and reducing visual fatigue caused by transient adaptation (the eye constantly adapting from high light levels on the task to low light levels on vertical surfaces in the area). Reducing shadows and strong contrasts, meanwhile, can increase visual comfort. A good example would be a windowed space where there may be an uncomfortable brightness contrast between the windows and adjacent wall spaces; placing light on these walls softens the contrast.
When walls are used as area light sources, it is important that the wall surfaces be as reflective as possible without being sources of glare. Avoid dark colors on walls and furniture except as minor accents and for flooring. Choose lighter colors such as white or certain pastels with a reflectance of 70 percent or higher. Choose matte finishes and avoid glossy finishes, which are strong candidates for reflected glare. Higher reflectance on ceilings and walls, particularly in spaces where those surfaces are used as area light sources—or reflecting surfaces for -lighting—can make a big difference in overall efficiency by reducing electric lighting needed to produce desired light levels.
In summary, wall lighting can help make lighting designs both energy-efficient and effective by placing visual emphasis on the spatial form, making spaces appear brighter and larger and improving visibility and visual comfort.
DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.