Electrical contractors don't like to brag, but they are enjoying a -significant and growing influence in lighting decisions. According to a Northwest Energy Efficiency Alliance study, contractors make design changes or suggestions in roughly one-third of their projects, either by substitution or original specification, and more than one-half provide lighting design and layout services, particularly in small- and medium-sized projects. (Compare those numbers to those in the profile on page 36, and you’ll get a compelling picture of contractor influence.)
Michael Lane, commercial lighting specialist for Seattle-based Lighting Design Lab, said the drive toward energy efficiency and the more recent sustainable construction movement often may put contractors in a position where they are asked to exceed the minimum requirements of the local energy code and maximize energy savings.
“The contractor who takes the time to learn what is energy-effective—efficient and appropriate for the task—will be providing a better product for their client. Big Brother is going to mandate it. Your clients are going to demand it. It’s time you start learning about it,” Lane said.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), in collaboration with government and other industry organizations, developed a series of Advanced Energy Design Guides that provides a prescriptive path for beating ASHRAE 90.1-1999, the national energy standard, by 30 percent in small office buildings, small retail buildings and K–12 school buildings.
Regarding lighting, this means reducing lighting power density from 1.3W/square foot to 0.9W/square foot. Lane said this can be done fairly easily with current technology. It’s just 0.1W/square foot less than 90.1-2004’s and California Title 24-2005’s 1W/square-foot limit.
In an office, it is assumed that the target ambient light level is 30 foot-candles and that the task light level on the desktop is 50 foot-candles. The guide recognizes distributing light on walls and ceilings as good design practice and, therefore, recommends one- or two-lamped direct/indirect fixtures mounted in continuous rows parallel to the windows, with some fixtures close to walls or installed with supplemental wall-wash fixtures.
“Pendant-mounted direct/indirect may be perceived as a high-end fixture, but it provides light on the ceiling, walls and task surface, making the space feel bright along with providing the recommended light levels,” Lane said. “This is a huge improvement in the quality of the lighting versus parabolic fluorescent, which has been used extensively in office spaces.”
To increase light levels with indirect lighting, the ceiling should have a 90 percent reflectance, if possible. It must have at least 80 percent. Most ceiling tiles have a 70–80 percent ceiling reflectance, while some manufacturers offer high-reflectance ceiling tiles. Walls and greater-than-2½-foot vertical partitions should have more than a 70 percent reflectance finish value.
The guide recommends high-performance T8 lamps, although T5 and T5HO lamps may be used as long as the fixture doesn’t have an open bottom. High-performance T8 lamps produce more light (3,100+ lumens) for the same wattage, paired with low-output (0.77 ballast factor) ballasts to save energy. T8 lamps should be operated by instant-start electronic ballasts, which provide higher energy savings, lower cost and parallel operation (if one lamp burns out, its companion will continue operating normally), although programmed-start ballasts are recommended to extend lamp life if the lamps are frequently switched by occupancy sensors.
The guide recommends, though seemingly contradictory to its intent, occupancy sensors set to medium to high sensitivity and a 15-minute time delay in open and private offices, with manual-on, automatic--off operation recommended for private offices. If occupancy sensors don’t make sense for an open-plan office space, use time-scheduling instead. Multilevel switching will generate energy savings while private offices are occupied. Similarly, undercabinet fixtures should include T8 lamps and a two-step ballast with the lower output level hardwired to allow bilevel switching control. Or, dispense with undercabinet fixtures altogether, and use articulated compact fluorescent task lights plugged into strips controlled by local occupancy sensors. Finally, use daylight dimming controls for direct/indirect fixtures placed within 12 feet of windows on the north and south perimeter zones, but note that 28W and 30W T8 lamps recommended by the guide are not compatible with dimming ballasts. Additionally, the photosensor should include a five-minute time delay to avoid cycling.
Overall, the guide provides a prescriptive lighting path to exceed 90.1-1999/2001 by 30 percent and 90.1-2004 and California’s Title 24-2005 by about 10 percent. It’s one way, but not the only way, to achieve 30 percent energy savings, Lane said, who contributed to the creation of a series of Lighting Design Lab commercial lighting guides offering additional paths to maximum energy savings as low as 0.75W/square foot.
DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.