The Process Of Lighting Design

Until 1973, daylighting was considered part of architectural design, not part of lighting design. Since an artificial lighting system had to be installed anyway, the practice was to ignore daylight, even to the extent of shutting it out completely. However, when the energy crisis hit in the mid-1970s, the extensive use of electrical energy in nonresidential buildings for lighting drove designers to integrate the cheapest, most abundant, and in many ways most desirable form of lighting, daylighting.

In an interview with Architectural Lighting in March 2001 (p. 22), lighting designer and architect William Lam stated:

Lighting design is about design and not engineering. Fixture selection and calculations should be the last thing you do. ... You have to understand about light and the physics of it, but mainly it's about having a vision. Lighting is applied perception psychology. . . . You have to understand the principles in relation to what makes something appear bright or dark, cheerful or gloomy—what makes a good or great luminous environment. It's not enough to have enough light and to avoid glare. Every room should be a positive experience for the activity with all elements of the space integrated.

The best lighting designs blend seamlessly into an overall interior design. Differences inherent in the objectives of the interior designer and the electrical engineer often lead to difficulties in achieving this goal. These differences have their roots in the training and functions associated with each profession.

The interior designer is trained to focus on aesthetics, to combine form with function, and to strive for an interior space that supports the client's image and facilitates the client's work process. Often, the electrical engineer's perspective may conflict with a design concept. Focused on technical issues, the electrical engineer's designs accentuate flexibility and efficiency. By standardizing lighting, fixture type, and fixture placement, and by minimizing the number of different light sources, the engineer promotes energy conservation and maintenance simplicity while providing enough light for the tasks at hand.

The designer and the engineer often have differing perspectives on their relationship with their client, and this can widen the gap between their approaches. The designer typically works with the client's executive management team to blend business objectives, work processes, and corporate image. The engineer might never meet this team, and frequently works with the facility manager, who may also be one of the interior designer's contacts. Facility managers are looking for a lighting scheme that is flexible, efficient, and low maintenance. A third client group is the users, including employees, whose needs focus on comfort and productivity. Unless the interior designer and the electrical engineer understand the needs of these three distinct client groups, they won't be able to work together effectively. When the interior designer and electrical engineer work well together, they help the client recognize and prioritize each client group's objectives, and achieve a design that integrates each discipline's strengths and meets the client's overall needs of all three groups—client, facility manager, and those who will use the space.

Professional lighting designers can help bridge the gap between the interior designer and the electrical engineer. With expertise in the technical aspects of lighting and strong resources in the aesthetic and functional aspects of lighting design, the lighting designer is able to see both perspectives. Add to this extensive knowledge of the fixtures available on the market and the ability to speak the electrician's language, and the lighting designer becomes an invaluable asset to the architect and interior designer.

Working through all these elements may add additional design costs to the project, but the results can be a significant benefit. When the design is based on a clear understanding and agreement about what benefits the client most, all parties involved will agree that an integrated solution, while it may sacrifice certain subgroups' objectives, will meet the project's overall objectives and serve the client's best interest.

Historically, the selection and location of lighting fixtures has been divided between architectural lighting and utilitarian lighting, with inadequate attention to the needs of specific visual tasks. Incandescent wall washers and other fixtures were used to emphasize architectural elements and provide form-giving shadows. Luminance levels, cavity ratios, foot-candles, and dollars dominated utilitarian lighting selection.

Fortunately, both trends have been largely eliminated. Thoughtful architects, engineers, and lighting designers led research into ways to satisfy real vision needs with minimal energy use. The 1973 Arab oil embargo spurred on the development of energy codes and of higher efficiency sources. The Illuminating Energy Society of North America (IESNA) is a research, standards, and publishing organization that develops stable scientific bases for lighting, while remaining aware of its artistic aspects. The combination of science and art make lighting design a truly architectural discipline.

The process of designing lighting for a large building involves an interaction between the designer of the lighting and other consultants. Central to the design is the connection between artificial lighting, the heating, ventilating, and air-conditioning (HVAC) system, and daylighting. From the owner's point of view, the initial and operating costs are key considerations. The architect will be concerned with the amount and quality of daylighting, and with the architectural nature of the space. The first step is to establish a project lighting cost framework and a project energy budget.

A quarter of the electrical power generated in the United States is used for lighting, an amount of energy equivalent to approximately 4 million barrels of oil per day. Of that amount, approximately 20 percent is used for residential lighting, 20 percent for industrial lighting, another 20 percent for lighting retail spaces, and 15 percent for school and office lighting. Outdoor lighting and other uses account for the other quarter of the en ergy used. Lighting comprises 20 to 30 percent of a commercial building's electrical energy usage; percentages are higher for residences and lower for industrial buildings. Good lighting design can save up to half of the electrical power used for lighting.

Lighting is a major contributor to the building heat load. Each watt of lighting adds 1 W (3.4 Btu per hour) of heat gain to the space. It takes about 0.28 W of additional energy to cool 1 W from lighting in the summer, but the added heat may be welcome in the winter. Reducing the lighting power energy levels to below 2 W per 0.09 square meters (1 square ft) in all but special areas results in less impact from light-generated heat on the HVAC system.

Fixture efficiency is directly affected by temperature. Fluorescent units operate best at 25°C (77°F), so removing heat is helpful even at low lighting energy levels. The most efficient way to remove heat is to connect a duct to the fixture itself, but this is expensive and immobilizes the fixture. An alternative is to use an exhaust plenum with air passing over the fixtures to pick up excess heat.

Lighting standards are set by a variety of authorities, depending upon the type of building, whether it is government owned or built, and where it is located. Two of the federal agencies that have specific requirements for lighting are the U.S. Department of Energy (DOE) and the General Services Administration (GSA). In addition to the National Fire Protection Association (NFPA) codes, which include the National Electrical Code (NEC), standards are set by the American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE), the Illuminating Engineering Society of North America (IESNA), and the National Institute of Science and Technology (NIST). In 1989, ASHRAE/ IESNA Standard 90.1, Energy Efficient Design of New Buildings, set lighting power credits for lighting control systems designed with energy conserving controls. Credits like these can help a designer meet the requirements while providing the lighting needed for tasks and for aesthetic impact. Local authorities may refer to the requirements of these organizations.

Energy budgets and lighting levels set by these standards affect the type of lighting source, the fixture selection, the lighting system, furniture placement, and maintenance schedules. State codes may regulate the amount of energy permitted for lighting in various occupancies. New York State energy guidelines, for example, set a maximum level of 2.4 W per square ft. With good design, lighting levels can be even lower than limits set by codes.

Once the lighting energy and cost budgets are established, the next step is task analysis. Lighting must provide an appropriate quantity of light for a specific task in a given area. Activities requiring greater visual acuity require higher illumination. The repetitiveness, variability, and duration of the task are also taken into account. Another consideration is the health and age of the occupants. In addition, the cost of errors caused by inadequate illumination is considered.

The amount of light should relate to the difficulty of the task performed. This depends upon the size of the object viewed, the contrast between the object and its background, and the luminance of the object. Luminaires should not be more than 20 times brighter than their background. No place in the normal field of view should have a luminance ratio greater than 40 to one.

Electrical engineers usually determine the amount of light needed by using an analytical approach. They establish numerical requirements, and manipulate the variables of sources, fixtures, and placement of units. An alternative approach is referred to as brightness design. The designer labels surfaces with the desired brightness and designs the lighting accordingly. Brightness design is highly intuitive, and requires lots of experience on the part of the designer.

During the design stage, detailed suggestions are raised, considered, modified, and accepted or rejected. The interior designer or lighting designer typically prepares a lighting plan (Fig. 34-1) and schedule that indicates fixture locations and selections. The designer then must coordinate his or her selections with the HVAC engineers, who will monitor power loads. The result is a detailed, workable design that may involve relocating a space or changing lighting or HVAC system details.

The design stage progresses through several steps. A lighting system is selected, which involves analysis of the light source, the distribution characteristics of the fixtures, daylighting considerations, electrical loads, and cost. Next, the lighting requirements are calculated. A pattern of fixtures is established and the architectural effects are considered. The interaction of the color of the light source and the color of surfaces is evaluated. Supplemental decorative and architectural (built-in) fixtures are then designed. The physiological and psychological effects of the lighting should also be considered, especially in spaces that are occupied for extended periods of time. Finally, the design is reviewed, and checked for quality and quantity of fixtures, esthetic effect, and originality.

During the evaluation stage, the design is analyzed for conformance to the constraints of cost and energy use. The results are provided to the architect for use in the final overall project evaluation.

Figure 34-1 Reflected ceiling plan with lighting.
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