Many spaces in buildings are only ocucpied from time to time, but must be lit at all times in order to meet life safety requirements found in most codes. When it comes to lighting in intermittently occupied egress spaces such as stairwells, meeting code and safety requirements are of utmost importance, but once those standards are met, there are significant opportunities to reduce energy use.

Several buildings on Harvard’s campus have installed bi-level lighting controls to address the fact that lighting in these stairwells is typically always on, yet the spaces are occupied only a fraction of that time. A comprehensive study via California's Lighting Research Program demonstrated the potential to reduce energy use between 40-60% by utilizing bi-level controls. As states adopt ASHRAE 90.1-2010, reducing lighting power in stairwells not designated for egress will be required. The updated standard states that stairwell lighting controls must be used to automatically reduce lighting power by at least 50% within 30 minutes of all occupants leaving (9.4.1.6).

Before making changes to lighting in egress areas, be sure to consult a licensed professional to ensure appropriate code requirements and lighting levels are being met and advise on placement of occupancy sensors. Massachusetts code currently references NFPA 101, which requires at least 1 footcandle (fc) on the walking surface at all times in egress pathways. During occupied periods, the same standard requires an illuminance of at least 10 fc. (7.8.1.3)

Many buildings leave stairwell lighting on at full power, 24 hours a day, to meet these requirements, yet the NFPA 101 allows the use of occupancy sensors “provided that the switch controllers are equipped for fail-safe operation, the illumination timers are set for a minimum 15-minute duration, and the motion sensor is activated by any occupant movement in the area served by the lighting units” (7.8.1.2.2). Additionally, the design must ensure that the system is "arranged so that the failure of any single lighting unit does not result in an illumination level of less than 0.2 ft-candle" (7.8.1.4)

There are many methods to provide bi-level dimming control in stairwells and corridors. The best solution for a specific project will depend on a variety of factors:

• Bi-level fixtures with integrated occupancy sensors: Many manufacturers now offer fixtures that are designed specifically to meet both code and efficiency requirements in typical stairwell configurations (i.e. one fixture at each landing). Multi-lamp fluorescent and LED technology are available.
• Retrofitting existing fixtures with occupancy controls: If the existing fixtures are reasonably efficient and in working order, it may be possible to add occupancy control and/or a dimming system without changing the entire lighting fixture. In corridors where some fixtures are already on a separate emergency lighting circuit, it may be possible to leave that circuit on at all times and shut down the non-emergency circuit when no occupants are present. 

Both wireless and hardwired remote occupancy sensor systems are available.

Incentives: The MassSave incentive program currently features a $75 per fixture incentive for retrofitting existing lighting in stairwells with integrated occupancy sensors, though only for fixtures that operate continuously.  Details on this and other incentives available in Massachusetts can be found on the MassSave website.

Life Cycle Costing: While many spaces are good candidates for bi-level lighting, not every corridor or stairwell renovation is economically viable, particularly when existing systems in a space already utilize efficient lighting technologies. By using utility savings calculations combined with reasonable equipment and maintenance cost estimates, it's possible to develop a comprehensive analysis that will show the true cost of ownership of both the existing and proposed systems over the expected life of the building.  Harvard maintains a free Life Cycle Costing Calculator that can be accessed here.