Stairwell lighting is typically operated continuously at full output in nonresidential buildings even though these spaces are only intermittently used. In recent years, lighting manufacturers have begun offering a solution that can reduce energy costs while providing satisfactory levels of illumination for emergency egress. These lighting fixtures adjust light levels based on occupancy.
The concept is simple. The lighting fixture provides a constant low level of illumination until the occupancy sensor detects occupancy, at which time it raises the light level. The result is ongoing energy cost savings. The Federal Energy Management Program rates this measure four out of five in cost effectiveness and five out of five in probability of success.
NFPA 101, the Life Safety Code, requires at least 10 foot-candles (fc) of illumination on the stair tread while in use (Section 126.96.36.199) and recognizes the use of automatic motion sensors as long as they provide fail-safe operation, activate the lighting upon occupancy, and keep the lights on for at least 15 minutes after the area becomes unoccupied (Section 188.8.131.52.2). Bilevel stairwell lighting, therefore, provides partial illumination—typically about a foot-candle—when unoccupied and until a person enters the stairwell. The lighting then increases automatically to 10 fc for as long as occupancy is detected in the controlled area. Of course, local codes vary. Some codes may allow the lights to be turned off completely.
Automatically controlled bilevel stairwell lighting will soon become required in most new nonresidential construction, as the Department of Energy recently recognized ASHRAE/IES 90.1 2010 as the new national energy standard. By Oct. 18, 2013, all states must institute a commercial building energy code at least as stringent as ASHRAE/IES 90.1 2010. For stairwell lighting, it requires automatic controls that reduce lighting power by at least 50 percent within 30 minutes of the controlled area being vacated.
According to the International Facility Management Association, stairwells account for roughly 2 percent of multistory commercial building floorspace, with an average of one lighting fixture per 58 square feet of stairwell. Studies suggest that the average stairwell is trafficked only 3–5 percent of the average day, resulting in significant energy savings. These savings typically have two components: an improvement in efficiency by upgrading from T12 to T8 lamps and ballasts and a reduction in light level during the majority of operating time. Manufacturers estimate savings potential of 70–80 percent, a number not quite achieved in various studies.
In 2003, the Lighting Research Center studied the use of bilevel stairwell lighting—specifically, LaMar Lighting’s Occu-smart bilevel T8 fixtures—in two New York City buildings and found energy savings of 53–60 percent. Subsequently, the Lawrence Berkeley National Laboratory studied the use of this product in four California buildings and discovered an average of 40–60 percent energy savings. A Pacific Gas & Electric study of the installation of stairwell fixtures by Wellmade Products at the Fillmore Center apartments in San Francisco calculated 66 percent energy savings.
Bilevel stairwell lighting is suitable for new construction and retrofits. The greatest opportunities are in stairwells that are lightly trafficked and receive no daylight; look beyond stairwells at other potential applications in utility spaces, such as laundry rooms. If an older installation using 4-foot T12 lighting, energy legislation affecting availability of T12 lamps and ballasts presents an opportunity to replace the entire fixture with one that has bilevel control capability, accelerating the energy savings for a likely reasonable cost premium. Note, if the sensor uses PIR sensing technology, it must have a line of sight with the occupant; the location of J-boxes in existing construction may not be optimal for this. Ensure that no “blind spots” exist and that the sensor activates the higher illumination level almost immediately after an occupant enters the coverage area. Wireless sensors provide flexibility to adapt coverage to the existing wiring and layout of the stairwell.
Lighting manufacturers offer a variety of approaches and options. Stairwell fixtures are available in 2-, 3- and 4-foot lengths; T8, T5 and T5HO lamping in various wattages; one or two lamps; step dimming, continuous dimming or switching; choice of low-end dim levels; integral or external wireless ultrasonic or passive-infrared (PIR) sensors; daylight sensing, ensuring the fixture is not brought to full output when sufficient daylight levels are present; white or clear prismatic lenses; wall or ceiling mounting (each with distinct coverage patterns for their integral sensors); 120-volt (V), 277V or universal voltage ballasts; optional vandal-resistant features; and optional emergency battery backup.
Columbia Lighting, for example, offers a switching option for when dimming is not practical or affordable; for this option, a 17-watt T8 operates continuously, joined by two 4-foot T8 lamps during periods of occupancy. Lutron’s PowPak Stairwell Solution uses continuous dimming ballasts operating with a wireless occupancy sensor that can be installed anywhere for optimal coverage.
Depending on the application, properly applied bilevel control can provide significant energy cost savings for stairwell in new and existing buildings.
DILOUIE, L.C., a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.