Luminaire-level lighting control (LLLC) has attracted significant interest among building owners and utilities as a simple path to maximize energy cost-savings from LED lighting installation. A study conducted by the University of Oregon in Eugene on behalf of the Northwest Energy Efficiency Alliance (NEEA), Portland, Ore., demonstrated that LLLC produced similarly substantial energy savings as a networked lighting control system, but at a lower cost.
LLLC features one or more sensors plus a luminaire controller and dimmable driver installed in each luminaire. This enables a control strategy where each luminaire can operate as an independent control zone, increasing energy savings by maximizing responsiveness. It is more commonly deployed in office spaces, where a typical luminaire serves 80–120 square feet. The sensor element may be responsive to occupancy and, if it is in a daylight zone, daylight. The control output may be on/off, multilevel switching or dimming or continuous dimming. Manual controls allow users to override the automatic control function.
LLLCs may operate independently or together by a connected layer consisting of a gateway to send and receive data, a server or cloud to store the data and software for programming, commissioning and potentially analytics. The control points may be addressable for assigning to sequences of operation and grouping in larger zones, with additional strategies such as scheduling, plug-load control and personal or institutional task-tuning control available.
NEEA wanted to determine whether LLLC installed in a one-for-one LED retrofit generated energy savings and lighting quality comparable to a more-comprehensive NLC-based redesign, while also comparing cost.
The study involved an 891-square-foot space: 33 feet wide east-west and 27 feet deep north-south, with perimeter glazing along the northern facade to allow daylight penetration. The existing lighting consisted of nine 4-foot indirect/direct pendant luminaires evenly spaced apart on a three-by-three grid and controlled by a manual wall switch. Four workstations were set up at the center of the space to simulate a typical open office space.
Five systems were installed and monitored—four LLLC and one NLC differentiated from the LLLC by installation of remote ceiling-mounted sensors (four occupancy sensors and two light sensors) and control zoning of luminaires in groups using software. The four LLLC solutions started with a basic luminaire with onboard sensors and luminaire controller and built up to networked luminaires for more sophisticated control. The NLC redesign also used a 1:1 luminaire replacement, but with the sensors installed remotely and grouped for occupancy and daylight control using software, while also yielding data used for space use and asset tracking. All five scenarios were compared to a fluorescent baseline based on each luminaire housing 32W T8 lamps powered by an electronic ballast. All were tuned to produce approximately 30 foot-candles of workplane illumination.
Current transformers monitored lighting power draw while lighting quality was analyzed. Study participant recruits performed computer- and paper-based tasks and answered questionnaires to provide subjective reaction to quality of light, brightness, light distribution, visual comfort and well-being. The researchers also quantified the time and ease of installation and cost.
The researchers discovered that all these systems produced substantial energy savings compared to the baseline. The LLLC systems generated 50%–74% energy savings for the control element alone, while the NLC redesign demonstrated 67% energy savings. Admittedly, the space was very well suited to LLLC compared to the NLC solution.
Savings were analyzed in three categories: savings due to daylight and occupancy sensing, savings due to institutional task-tuning (high-end trim) and savings due to all control measures. The highest-performing LLLC was a basic 1:1 replacement geared up with additional features, such as scheduling, task-tuning, demand response, plug load control and energy monitoring. The NLC fared best for savings due to institutional task-tuning but lowest for daylight and occupancy sensing, likely due to fewer sensors and therefore less granularity in the control response.
Each system was installed smoothly and without delays, though acquiring the equipment was challenging due to compatibility issues, accuracy of the specification and miscommunication along the supply chain. The time and complexity involved in programming and commissioning varied across the systems, with the main challenges arising from insufficient hardware and software documentation. With an installed cost ranging from $6.04 to $7.44 per square foot, the LLLC solutions in this study proved more cost effective, while the redesign system cost $17.57 per square foot. Regarding lighting quality, participants valued the new indirect/direct lighting, though without any clear preference for any of the five systems.
Check out the study results at https://bit.ly/36mxMcr.