Another contribution to the March issue of The Electrical Distributor provides a primer on lighting design. Reprinted with permission.
It’s often said that lighting is as much an art as it is engineering, but the art of design can be reduced to a series of guiding principles. By understanding these principles, electrical distributors demonstrate expertise and differentiate themselves. They can engage owners in a conversation that starts with application needs and ends with equipment sales.
What lighting can do
Light is a commodity that should be purchased at the lowest possible cost, but lighting is a business asset that should be carefully considered for investment with the right design and equipment.
The large majority of our impressions of the world come through our eyes, and light is necessary to vision. Light is therefore the medium through which a majority of people perceive the world.
“Lighting” is the application of light to spaces. Where the light is placed, at what relative intensities, and in what direction, can have a major impact not only on vision and visual comfort, but perception. Not just light, but the lighting equipment itself can also affect impressions of the space and its owner.
Lighting, therefore, can impact satisfaction, visibility, task performance, safety, security, sales, mood and atmosphere, aesthetic judgment and social interaction. It also tells a story about the space, whether a given store is likely to be focused on discounts or high-end products, or whether a restaurant is selling fast food or a fine dining experience.
Color perception: For an object to be perceived a certain color, that color must be present both in the object and the content of the light striking it. Designers are concerned with color appearance (measured in correlated color temperature, or CCT) and color fidelity, or color rendering compared to an ideal source (measured on the color rendering index, or CRI). The lighting industry is now evaluating a proposed metric capturing saturation as well. Changing CCT, CRI and saturation can have a big impact on how people, objects and spaces appear, enhancing or muting or even distorting their colors.
Focus: The human eye is naturally attracted to the brightest area in the field of view. By focusing a higher intensity of light on certain features in a space, we can make them focal points, directing attention to them, and establish a visual hierarchy. For example, we could promote a key merchandise display by focusing a higher intensity of light on it.
Space perception: The pattern of light in a space can stimulate a psychological response (see Table). For example, bright uniform lighting, with light placed on walls and even the ceiling, can make a space appear public and visually larger in a lobby. Conversely, lower-intensity lighting at the task with a little perimeter lighting can create feelings of intimacy in a fine restaurant.
A space’s lighting defines its personality and how people perceive it, which in turn affects how they feel about being there. Below are various lighting effects that can take the same space and transform it into different environments.
Modeling: The contrast of light and shadow can reveal texture and add depth to faces, objects and surfaces. For example, washing a brick wall with light will visually flatten its texture by reducing shadows, while grazing it at an angle will enrich its texture. As another example, strong downlighting on a face can produce shadowing at the eyebrows, nose and wrinkles. Modeling is effected by relative intensities and direction of light, with the light distribution characteristics of the light source being an important factor.
Upper left: statue lighted with diffuse lighting only, which results in a lack of definition. Upper right:
statue lighted with diffuse lighting with sidelight, balancing definition without harsh shadowing. Bottom left: statue lighted with downlighting only, which produces unflattering shadows. Bottom right: statue lighted with uplighting only, which makes the face appear sinister. Image courtesy of Naomi J. Miller, FIES, FIALD, LC.
Point sources, such as incandescent lamps and LEDs, are small lamps that can produce pronounced shadows. Linear sources, such as fluorescent lamps, produce diffuse light output from the source’s surface, which softens shadows. Area sources are large surfaces that emit highly diffuse light, such as a ceiling reflecting light from an indirect light source.
Left: objects lighted by a point source. Middle: objects lighted by a linear source. Right: objects lighted by an area source. Image courtesy of Peter Ngai.
A light conversation
Lighting design is the process of delivering lighting to spaces. It begins with a conversation with the owner about organizational and user needs. Who will be using the space? What are their lighting needs? What are the space characteristics? What business goals should the lighting support? What does the owner want the space to communicate? How important is energy efficiency and ease of maintenance? What restrictions apply, such as energy codes and budget?
Layering with light
Properly lighting a space often involves layering of general/ambient, task and accent lighting.
General lighting: This primary layer provides sufficient light to perform visual tasks, ambient light for safe circulation, or both. It is usually provided by overhead equipment. General lighting is typically diffuse and uniform.
General lighting typically falls into one of three categories based on its light emission: direct, indirect or some combination of the two.
Direct lighting distributes all or nearly all light downward toward the task. The light may be concentrated or spread, depending on the optics used. It’s very efficient but poses risks of direct glare, scalloping on nearby walls, and pronounced shadows. Indirect lighting distributes all or nearly all light upward toward the ceiling and nearby walls, which is then reflected into the task area. Indirect lighting provides very soft light distribution, which can promote visual comfort, but risks making the space appear visually flat.
Many luminaires, known by various terminology, emit light in both directions. Traditionally, semi-indirect luminaires emit 60-90 percent of their output up and 10-40 percent down. Direct-indirect emit roughly equally up and down. And semi-direct emit 60-90 percent of their output down and 10-40 percent up. Commonly, however, these luminaires are broken into two types: direct/indirect, a luminaire that emits more downlight than uplight, and indirect/direct, which emits more uplight than downlight. The downlight component provides efficient task lighting with modeling definition, while the uplight component provides diffuse ambient illumination for visual comfort.
Supplementary task lighting: This primary layer provides higher light intensities at the task. It is usually provided by localized equipment such as task lights, of which there is a wide variety.
Accent lighting: This primary layer is used to draw attention important objects, displays, artwork, architecture and areas by focusing a higher relative intensity of light on them. It is often provided by equipment such as directional lighting with varying beam spreads allowing precise control over what is being lighted. In applications where displays are expected to move, such as a retail store, flexible (aimable and/or movable) lighting is recommended. A particular accent lighting technique is framing, in which a recessed or surface-mounted light projector, fitted with adjustable shutters, precisely focuses intense light on an object such as a wall painting.
By separately controlling these layers at different intensities, a variety of scenes can be produced, providing flexibility to support various space needs.
Aside from the basic lighting layers, various techniques can be used to achieve specific lighting effects. These include downlighting, wall washing/grazing, cove lighting, uplighting, silhouetting and sparkle/glitter.
Downlighting: Downlighting is popular technique that places light below the light source and is available from a variety of lighting equipment, from downlights to recessed troffers. The light can be soft and diffuse for visual comfort in a space with critical visual tasks, or intense and non-diffuse to promote a visually stimulating atmosphere.
Downlighting that isn’t balanced with other light can produce unwanted shadowing on faces. Downlights installed near a wall can produce tall and thin scalloping, which is generally undesirable.
Wall washing and grazing: Wall washing involves uniformly lighting a wall from top to bottom in a graded wash. This “washing” eliminates shadows, resulting in a smooth, visually flat appearance. It’s therefore best suited to flat walls. Light sources must be placed a sufficient distance from the wall and close enough to each other to ensure a good wall washing effect.
Wall grazing is similar to wall washing, but the light source is placed closer to the wall, which accentuates shadows and thereby reveals texture. It’s therefore best suited to textured walls such as brick and stone. The light source can be placed at varying distances from the wall, changing the angle and thereby the amount of shadowing that is produced.
Cove lighting: Cove lighting involves illuminating perimeter coves. This highlights the architectural feature and sheds light on the ceiling, which is reflected into the space as indirect ambient light.
Uplighting: Uplighting places light above the light source. It’s not very popular but can be effective for certain applications, such table candlelight and highlighting architecture, plants and trees.
Silhouetting: Silhouetting involves backlighting an object with either no or reduced frontal lighting, rendering it in silhouette. The backlight can be intense (which clarifies the object) or diffuse. This technique is typically used for illuminating artwork, branding or architecture for aesthetics.
Sparkle/Glitter: This is producing tiny points of glare for visual interest and to produce a sense of elegance. Examples include some chandeliers and sparkle on restaurant silverware.
This private office is lighted to 50 footcandles of task illumination using four different designs featuring troffers, downlights, parabolic troffers and linear indirect. The result is a space that appears differently in terms of brightness, aesthetics, spaciousness and visual comfort. Image courtesy of Leslie North, PE, LC, LEED-AP and Carla Bukalski, PE, LC.
The aesthetics of visible lighting equipment will also have an impact on how the space and its owner are perceived. A decorative, sparkling chandelier in a hotel lobby can convey elegance, for example. Linear suspended luminaires instead of troffers in an office conveys a cool, high-tech look. Similarly, the arrangement of luminaires conveys an aesthetic impression. Luminaires should always be placed in a way that is not visually jarring (unless the designer wants it that way for some reason).
Lighting is far more than lumens and watts. It is the application of light to spaces to support the owner’s goals and user needs. By understanding the various techniques and principles used to produce different lighting effects, owners can be engaged in educated sales conversations that start with their needs.