Hard Numbers: Responsive Lighting

Estimating lighting control energy savings is challenging, as actual savings depend on application characteristics, such as occupant behavior, building design, site orientation, daylight apertures, interior reflectances, device settings and level of commissioning. But what about measuring savings after responsive lighting is installed?

In its 2011 report, “A Meta-Analysis of Energy Savings from Lighting Controls in Commercial Buildings,” the Lawrence Berkeley National Laboratory (LBNL) analyzed 240 energy-savings estimates from 88 papers and case studies, focusing on actual field installations as opposed to simulations, to produce best estimates of average lighting energy savings for four primary lighting control strategies:

• Occupancy-based control (occupancy sensors, time scheduling): 24 percent

• Personal tuning (occupant control of light levels using dimmers, wireless switches, workstation-specific control, preset scene control): 31 percent

• Daylight harvesting (photosensors): 28 percent

• Institutional tuning (light levels tuned to space needs by application, reduction of ballast factor, task tuning, lumen maintenance, group controls): 36 percent

The LBNL report also estimated 38 percent savings for using multiple strategies (any combination). Get the report at http://efficiency.lbl.gov.

In September 2012, LBNL produced another report, “Responsive Lighting Solutions,” for the General Services Administration’s (GSA) Green Proving Ground program, which evaluates innovative building technologies and supports GSA performance specifications development. The study provides insight into the viability of highly responsive lighting control systems.

Five federal buildings were retrofitted for the study. The existing lighting systems were diverse, mostly recessed fixtures, with control limited to occupancy sensor and time scheduling applications. The systems were replaced with several retrofit options, the most notable being Philips Lightolier suspended 4-foot direct/indirect three-lamp T8 fluorescent fixtures—with two lamps dedicated to downlight and one to uplight—and equipped with onboard digital (LumEnergi iB-100) dimmable ballasts and passive-infrared occupancy sensors. The ballasts were tied to a LumEnergi digital lighting control system for task tuning (for application needs) and personal control. The system operator could access lighting control settings using a computer. The installation primarily consisted of the new fixtures and controls, communications wiring, and system setup. The manufacturer and an electrical contractor verified the settings and operation.

Other options included 8-foot workstation-specific fixtures above cubicles in open offices and 2-by-4 and 2-by-2 recessed fixtures in private offices, conference rooms, transition spaces and similar environments. In private offices, daylight harvesting added a control strategy using photosensors. Recessed 26-watt compact fluorescent downlights were placed in corridors and other transitional spaces.

Task tuning was implemented based on task evaluation and user discussions, establishing default settings. In fixtures over open cubicles, for example, installed power was reduced to 50 percent for the downlight component and 30 percent for the uplight component. In interior private offices, interior conference rooms and transitional spaces, 50 percent. In perimeter private offices and conference rooms, 30–70 percent.

Nonetheless, light levels generally improved. A desktop light level sampling revealed 42 percent of the preretrofit fixtures provided light levels higher than the IES-recommended 35 foot-candles, while 60 percent of the workstation-specific fixtures met that goal on the default dim settings. With light level controls, users displayed a preference for lower light levels at 56 percent.

The fixture layout change increased the lighting power density (watts per square foot) significantly, but controls use achieved energy savings ranging from 27–63 percent. Spaces with long operating hours, high utility rates and variable occupancy patterns realized higher savings.

Occupants were surveyed. Respondents demonstrated higher satisfaction with the new lighting system, generally finding it provided better quality light with less glare. Satisfaction tended to increase as users had a chance to acclimate to the new system. However, a significant number of users indicated the occupancy sensors were not sensitive enough and would turn off while the space was still occupied. Additionally, occupants said they wanted more control of their overhead lighting. While the system offered this capability, open office occupants could not adjust light levels without going through a systems operator due to GSA security restrictions. Full occupant control could have elevated occupant satisfaction further while increasing energy savings.

The researchers cited several lessons that could have improved results: personnel training, more thorough commissioning and built-in diagnostics, and more intuitive operator interface and settings. Overall, however, they concluded that the study demonstrated responsive lighting systems have proven to achieve deep energy savings while providing comparable or improved light levels and increased occupant satisfaction.

Download the report at www.gsa.gov/portal/content/121195.

About the Author

Craig DiLouie

Lighting Columnist
Craig DiLouie, L.C., is a journalist and educator specializing in the lighting industry. Learn more at ZINGinc.com and LightNOWblog.com .​

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