Energy-Efficient Lighting Design

April 21, 2009

Better, more efficient lighting can have a positive impact on organizations, their employees, and their clients

Architects play a key role in better lighting design that results in significant reductions in operating costs, electrical consumption, and greenhouse-gas emissions, along with increased occupant comfort and productivity. Better, more efficient lighting can have a positive impact on organizations, their employees, and their clients.

The largest energy consumers in the United States are office, retail, and service buildings. Office buildings consume the most, accounting for 19 percent of all commercial energy consumption (44 percent of that is for lighting). Retail and service buildings have the largest energy bills, and they account for 18 percent of all commercial energy consumption (59 percent of that is for lighting). Retail buildings are responsible for the second largest percentage of greenhouse-gas emissions. The average age of commercial buildings in the United States is 30.5 years, and many of these buildings have inefficient lighting and lack smart controls.

Energy-Smart Buildings and Light Quality
Architects of energy-smart buildings typically specify automated controls like occupancy sensors and bi-level switching to reduce energy consumption. Occupancy sensors in unoccupied offices or infrequently used areas, and bi-level switching in parking lots or retail areas, can lower energy usage by up to 30 percent. Bi-level switching can lower lighting levels by 50 percent in unoccupied sales areas or parking lots, and switch to full lighting levels as occupants approach. Energy-smart office buildings can actually enhance the comfort and performance of workers, and boost productivity. Many of the same measures that improve energy performance also make it a more comfortable place to work. Energy-efficient features also help your clients attract and retain tenants.

Color rendering index (CRI) is a measure of the quality of color light, devised by the Intl. Commission on Illumination (CIE). CRI values range from 0 (for a source like a low-pressure sodium vapor lamp, which is monochromatic) to 100 (for a source like an incandescent light bulb or a source with color temperature similar to daylight). CRI is a quantitatively measurable index, not a subjective one. A standard “cool white” fluorescent lamp will have a CRI of near 62. Corrected color temperature (CCT) is a characteristic of visible light that’s color balanced, where all colors are present or neutral. CCT is a measurement on the Kelvin (K) scale that indicates the warmth or coolness of a lamp’s color appearance. Typically, a CCT rating of below 3,200K is considered warm, while a rating of above 4,000K is considered cool.

CRI and CCT are often combined into a three-digit number: The first digit represents the CRI, and the last two digits represent the CCT. This combined value is helpful in selecting spectrally enhanced lighting (SEL). Efficacy, or the ratio of the light output to the power used, is measured in lumens per watt (lm/w); the higher the efficacy, the more efficient the fixture. Combining high efficacy with spectrally enhanced lighting has resulted in savings of 17 to 30 percent by allowing lower lighting levels in the typical office environment with no significant difference in user/occupant acceptability.

The design method for SEL provides a reliable model for predicting light-level differences and energy-savings potential. Projects with SEL systems are an economic and viable solution for many commercial buildings. Be sure to inform building owners that the installation costs are no higher than other forms of lighting retrofits, making the incremental energy savings a no-cost benefit. For buildings with T12 lamps, spectrally enhanced lighting can provide a 71-percent rate of return on the investment over the life of the system. A 30-percent rate of return is obtainable for buildings with existing T8 lamps. For new construction, SEL provides a design tool that can reduce initial construction costs and provide peak-load reductions and long-term energy savings for building owners and operators.

Using SEL will maintain the same level of visual ability in existing or new facilities with reduced lumen output through increased brightness perception and visual acuity provided by the enhanced spectrum. This reduction in lumens translates directly to energy savings. Approximately half of the savings in a case study on office buildings was due to the use of SEL, while the other half was attributable to the change from the pre-retrofit T12/magnetic ballast system to the post-retrofit T8/electronic ballast system. SEL lamps with electronic instant-start ballasts cost approximately the same as installing more traditional lighting systems, but SEL lamps offer immediate payback.

Potential energy savings depends on the existing lighting or the proposed lighting for new construction, and the illumination requirements. Energy savings are achieved through a combination of technologies ranging from simple lamp/ballast change-outs to implementation of smart controls to integration of daylighting strategies. Depending on the type of occupancy and new or existing conditions, these lighting strategies differ. Understanding and documenting what each owner will need for efficient delivery of the facilities mission, staying in budget, and occupant comfort are essential, as is the knowledge of various lighting and control nuances, and their associated implementation strategies. Making sure that all benefits are achieved requires a team approach to gain the maximum benefit from the investment (see below for more on this).

Implementation of smart design, correct installation, and verification of performance provide lower construction and retrofit costs, permanent reductions of electric load and operating costs (thereby automatically reducing greenhouse-gas emissions), and lower demand-load costs at peak hours. The return on investment, positive occupant perceptions, and savings to the environment can be quite substantial.

Select a Dedicated Team
How lighting systems are designed depends on many factors, ranging from aesthetics to occupancy types to specific task requirements. Combining daylighting with artificial lighting increases the complexity of the design, and rewards with improved occupant satisfaction and lower operating costs down the road.

A team approach is required to successfully accomplish cost reductions and positive business and social benefits. This team typically consists of architects, lighting design professionals, electrical contractors, commissioning authorities, and operation and maintenance staff to obtain the maximum benefit of a lighting retrofit. If the lighting modifications are part of a grander plan, or a new building, a full team of design, construction, and commissioning professionals would be needed as dictated by the project scope.

It’s important that the team be truly committed to the project goals and have experience with high-performance building design and construction. Communication and team dynamics are keys to success. The importance of defining and documenting a project’s objectives and criteria can’t be overstressed. Using the commissioning process to develop the owner’s project requirements (OPRs) organizes and clearly states the project’s design and performance requirements. Referencing the OPRs in the project contracts will ensure that all team members have a solid understanding of project objectives and criteria. It’s typically necessary to modify standard agreements to include the OPRs, as well as the consequences if the design and construction teams don’t meet these requirements.

In selection of team members, it’s recommended that the team include an independent lighting designer and an independent commissioning authority (CxA). The lighting designer shouldn’t be tied to a specific manufacturer, and must be able to provide guidance on daylighting, fixture selection, layout, and control strategies. The independent CxA, who reports directly to the owner, must have an in-depth knowledge of lighting design and controls.

Jay Enck is principal and founder at Atlanta-based Commissioning & Green Building Solutions Inc. (CxGBS).

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