Lighting Green Buildings

By Robert Paul Dean, AIA, CSI, CCS, and Susan McClendon, RA, CSI, CCS

Lighting design is only one of many opportunities for achieving more environmentally friendly buildings, but its effects are surprisingly pervasive. In addition to greatly improved energy conservation, good lighting design can improve neighborhoods by reducing light pollution and can improve interior environments by better balancing natural and artificial illumination and offering inhabitants better lighting control.

New light sources, in addition to being more energy efficient, can reduce toxic waste, and fixtures, fittings, and room finishes can offer optimal light distribution and minimal waste. This article will examine some of the ways in which good lighting design can contribute to the goals of green building and help achieve certification under various LEED and Green Globes programs.

What is LEED^®?
An acronym for Leadership in Energy and Environmental Design, the LEED program is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings that was created and sponsored by the U.S. Green Building Council (USGBC). The overall LEED program promotes a whole-building approach to sustainability by recognizing performance in five key areas of human and environmental health: sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality. In fact, there are currently nine specific LEED programs that address a variety of situations and building types, with other programs still in development. The original and most prevalent LEED program is LEED-NC, which was developed for new commercial construction and major renovation projects. Other commonly applicable programs include LEED-CS, for core and shell development projects, LEED-CI, for commercial interiors projects, and LEED-EB, for existing building operations and maintenance. Each of these LEED programs includes a rating system in the areas of sustainability mentioned previously and offers certification at different levels for buildings that achieve a specified minimal number of points.

Whether or not LEED certification is being sought for a particular project, the goals of the program and the areas in which points can be awarded are worthy of consideration for virtually any project. Regarding lighting goals, what may be surprising to many is the fact that LEED points can be awarded in several different areas - not just for improved energy efficiency. These areas include Sustainable Sites, Energy & Atmosphere, Materials & Resources, and Indoor Environmental Quality, in addition to potential points for Innovation & Design Process.

What is Green Globes?
Green Globes is an online building and management environmental audit that helps property owners and managers measure the environmental performance of their buildings against best practices in areas such as energy, water, hazardous materials, waste management, and indoor environment. Developed initially in Canada, it is now also being used in the United States and the United Kingdom. In the United States, Green Globes Design is both a guide for integrating green design principles and an assessment protocol. Using confidential questionnaires for each stage of project delivery, the program generates comprehensive online assessment and guidance reports to help the designer achieve a building that will be energy- and resource-efficient and healthier to work or live in, as well as save operational costs.

Green Globes offers a third-party verification and certification program, but even without certification, the system is useful for assessing a design in terms of its environmental impact and for obtaining suggestions for improvement. For lighting design, Green Globes offers strategies that are similar in scope to those included in the various LEED systems related to site design, material choices, energy reduction, and interior environment.

Green Site Considerations
An underlying concept in both LEED and Green Globes is that a sustainable building site should minimize light pollution from both the building interior and from exterior light sources. Light spillover should be minimized to improve night sky access, improve visibility through glare reduction, and reduce impact on neighboring property and the nocturnal environment in general. To accomplish these goals, lighting for a sustainable building should be designed to reduce the amount of light emitted horizontally or near horizontally, and fixtures should be located to keep light levels at the perimeter of the property very low.

For interior lighting with direct line of sight to exterior transparent or translucent openings, fixtures should be selected that minimize illumination in the direction of the openings. Preferably, the lighting should be automatically controlled to turn off after business hours, with manual overrides of limited duration. For exterior lighting, the design should include only such illumination as needed for safety and security, with lighting power densities lower than permitted under ASHRAE/IESNA standards. Both the LEED and Green Globes systems call for extremely low footcandle levels at site boundaries for park and rural settings, with moderately higher levels permitted in residential zones and somewhat higher levels in commercial and entertainment districts. Suggested means for achieving these goals include selection of full-cutoff luminaires and low-angle spotlights, use of low-reflectance exterior surfaces, and restriction of lighting to critical areas.

Reduced Energy Requirements
Designing a building to optimize energy usage is a complex process that involves consideration of the basic shape of the building, the choice and distribution of materials, and the selection and control of its various mechanical and electrical systems. With artificial lighting, the goal of energy optimization should involve designing appropriate ambient light levels for spaces of different functions, using fixtures that direct light where it is needed, using task lighting where possible, selecting more efficient lamps, and employing controls that automatically turn off lights when they are not needed.

Traditional incandescent lamps are clearly on the way out, not only in commercial construction but also in residential applications, due to their poor efficiency. Both Canada and Australia have recently enacted legislation encouraging the use of alternatives and banning the future sale of incandescent lamps altogether. Newer light sources are now available with much higher efficacy, including compact fluorescent lamps (CFLs), a wide variety of high-intensity discharge (HID) sources, and light-emitting diode (LED) sources. High-efficiency linear fluorescent lamps are also now available with better color rendering than provided by earlier models.

Fluorescents and traditional "bulb"-shaped light sources emit light in all directions, so inevitably much of the light is wasted within the fixture or otherwise lost. For many fixture types, including recessed downlights and troffers, it is not uncommon for as much as 50 percent of the emitted lumens to be lost. Some newer fixture designs minimize wasted lumens by more efficiently directing emitted light to worksurfaces, producing a higher coefficient of utilization (CU). In some situations, newer light sources such as LEDs can provide even higher application efficiency because of the directional nature of their light emission.

Designing spaces that are well illuminated yet use minimal energy can be a challenging task because of the many variables that are involved. In addition to those already mentioned, factors such as room proportions, reflectivity of room sources, and mounting height of fixtures should be taken into consideration. The results can be even more striking, however, when savings in air-conditioning costs are also factored in. More efficient lighting systems can significantly reduce the size and energy requirements of a building's HVAC systems.

Controlling Lighting for Reduced Energy Usage
It should probably go without saying that significant energy savings can be achieved by turning off lights when they aren't needed. Excessive switching can increase wear and tear on light sources and ballasts and reduce lamp and ballast life. In virtually all cases, though, it is more energy-efficient to turn lights off if not needed again for more than 20 minutes. The need for turning off lights at the end of the workday should be obvious, but without automatic switching it frequently doesn't happen. Situations in between may call for different strategies, but many experts advocate turning off incandescent and fluorescent lights whenever they are not needed. The savings in energy and the extended calendar life of the lamps will almost always offset the reduction in lamp life caused by frequent switching. HID lamps, on the other hand, should typically not be switched off unless the shut-off period is more than 15 to 20 minutes.

One way to encourage the practice of turning off lights is to add more switching circuits. By putting fewer lights on each switch, it will at least be possible to turn off lights in areas or spaces where lights are not needed. Occupancy sensors and timed switch controls are also a good idea in many situations, eliminating the problem of occupants forgetting to turn off lights.

Daylighting as a Green Building Strategy
The goal of proper daylighting design is to shape and fenestrate a building in such a way that enough natural light is admitted under most circumstances to allow building occupants to work easily. The main difficulty is how to admit enough daylight without too many undesirable side effects.

When daylighting goals are included in the building program, the energy optimization design process becomes even more complex than when artificial lighting alone is considered, and it involves more trade-offs. Building configuration, exterior wall area, and even choice of interior finishes and colors are affected by the desire to reduce dependence on artificial illumination. Buildings can be designed to admit sufficient natural light for most tasks, but glazing systems must be carefully selected, oriented, located, and shielded if necessary to admit sky light and reflected ground light while blocking direct solar heat gain. In optimizing overall building energy use, care must be taken to balance transparent and translucent portions of the building skin with opaque portions that can be designed to achieve much higher thermal resistance.

The orientation of glazing is also a significant factor in successful daylighting design, and the same strategies will not be equally successful on different elevations of a building. For example, exterior shading devices or interior light shelves that work well on a southern exposure will be ineffective if repeated without changes on east and west elevations. Increasing window area is not always the best way to improve natural lighting. Window shape and location in the exterior wall are often more significant in assuring better daylight distribution within the interior. In addition, the design must take into account the important goal of reducing glare from both natural and artificial sources.

Some of the design strategies typically adopted for improved daylighting conflict with other goals for green building. For instance, an increase in the building's perimeter to permit additional window area conflicts with the goal of reducing the size of a building's footprint and its impact on the building site. It also conflicts with the goal of minimizing the area of the building envelope for reduced energy needs. Sloped ceilings to direct more natural light deeper into a space can result in increased floor-to-floor heights, more exterior wall, and higher material costs. The ratio of exterior envelope area to floor area is almost invariably much higher in buildings designed for daylighting, so energy requirements for heating and air-conditioning also tend to go up. Achieving a design that reduces the overall energy budget while permitting most tasks to be accomplished without artificial lighting therefore requires a delicate balancing act.

Skylights can be successfully employed for daylighting one-story buildings and the top floor of multistory buildings, and devices such as tubular skylights can admit natural light into interior spaces on lower floors. Selection of glazing materials must also be carefully considered to achieve an appropriate balance of thermal resistance, shading coefficient, and visible transmittance, and this balance may vary with location. Glazing at or near eye level, for instance, typically should be transparent, but translucent or reflective fenestration above high level and for use in skylight glazing may be more energy efficient.

A successful daylighting design must incorporate integrated artificial lighting for the inevitable bad weather days and for use after normal operating hours. Incorporating automatic sensors and dimmable ballasts, fixtures, and controls for this purpose will increase first costs but can typically be shown to reduce overall energy needs and thus reduce operating costs.

Reducing Toxic Waste from Lighting
Another goal of green building design is reducing the toxic waste from the construction and operation of a building over its lifetime. Fluorescent lamps, including compact fluorescent lamps, employ mercury for their operation, as do sodium vapor high-pressure lamps. Mercury is a toxic heavy metal and poses the greatest hazard to pregnant women, children, and infants. Landfills often refuse standard fluorescent and sodium vapor lamps because of their high mercury content.

The amount of mercury in a standard lamp can vary significantly, from as little as 3 milligrams to as much as 46 milligrams. Modern fluorescent lamps use much less mercury than their predecessors, but there is still room for improvement. A standard 4-foot T12 fluorescent lamp contains about 12 milligrams of mercury, but alternatives are available with as few as 3 to 4 milligrams. Compact fluorescent lamps and sodium vapor lamps are also now being manufactured with far less mercury, intended to provide just enough to last for the expected lamp life.

With the recent availability of these high-efficiency, low-mercury alternative light sources, anyone interested in green building design should give serious consideration to specifying them for new construction, as well as for remodeling and retrofit applications. The LEED-EB Green Building Rating System for Existing Buildings includes as a prerequisite the requirement that a toxic material source reduction program be established and maintained to reduce the amount of mercury brought into buildings through purchase of lightbulbs (actually fluorescent lamps). This system also awards up to one point for a further reduction in mercury introduced through the lighting system.

Conclusion
Good lighting design can be compatible with the broader goals of green building. For maximum impact, the overall lighting goals must be addressed at the earliest stages of design because the very shape, orientation, and volume of the building can be affected by lighting considerations. Optimizing energy usage will call for careful fixture and lamp selection and will also affect room shape and room finishes, as well as lighting controls. Whether or not certification under LEED or Green Globes is being sought for a particular building, the lighting strategies promoted by these systems should be given serious consideration by design professionals and building owners interested in reducing operating costs and minimizing environmental impact.

Robert Dean ([email protected]) is an architect and president and chief operating officer of BSD. He is responsible for business administration and new business development and is also one of the most experienced and knowledgeable experts on automated specification systems in the country. Susan McClendon ([email protected]), a registered architect, is executive vice president of BSD. She is project manager for BSD SpecLink®, which now includes CSI-DBIA's PerSpective®. She manages the ongoing data development and updating of BSD SpecLink and also manages the maintenance of BSD's website.

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