Analog 0-10V control is the most commonly available option offered by North American manufacturers of LED luminaires and lighting controllers, even as LED systems have adopted modern digital network interfaces and luminaire-level sensors. Predicting light output and input power at any particular 0-10V control voltage is difficult due to dependencies on LED driver design and loading, and in practice the performance across luminaires can be inconsistent. Unpredictable and varying luminaire responses to input control signals—and a standard practice that does not compensate for these variations—can result in unexpected and undesirable performance. Moreover, energy and cost savings estimates associated with reduced lighting levels may not be realized.
To improve understanding and possibly resolve the shortcomings of 0-10V products, the Department of Energy recently published the results of a study conducted by Pacific Northwest National Laboratory (PNNL). The study characterized 23 LED streetlights that claimed dimmability via a 0-10V interface, quantified the performance variation found in market-available LED drivers, and explored the potential impact of the most recent 0-10V voluntary standard, ANSI C137.1-2022.
The study results and recommendations for driver and luminaire manufacturers, developers of connected lighting systems, and standards development organizations offer a potential path toward more accurate and consistent dimming performance across all luminaires in a lighting system, guaranteeing the delivery of expected light levels, energy, and cost savings. For example, the ANSI C137 committee is reviewing these findings as they consider updates to the standard.
Key findings
In a nutshell, PNNL’s study found the variation in luminaire response to 0-10V control signals was substantial. Across all the luminaires and tested control voltages, the range of relative power draw was on average ~53 percentage points. Nineteen of the 21 LED drivers were evaluated for ANSI C137.1-2022 voluntary standard compliance and nine of the 19 were found to be noncompliant. The range of relative power draw across all tested control voltages for the 12 luminaires containing ANSI C137.1-2022 compliant LED drivers was on average ~47 percentage points. From this limited testing, it appears that adoption of the ANSI C137.1-2022 voluntary standard will have a positive impact on market-available products (i.e., a reduced variation in response to a given control voltage) but will not necessarily result in uniform or predictable performance.
If controllers that operate luminaires with 0-10V interfaces are not calibrated to the unique control signal responses of those luminaires and controllers are configured with the expectation of a linear response from 0% relative light and power at a 0 V control signal to 100% relative light and power at a 10 V control signal—as is common in real-world products and system configurations—then unexpected lighting levels or energy performance are likely to occur. When implementing energy saving control strategies, such unexpected energy performance may compromise the realization of energy saving goals.
The study explored the potential impact of using 0-10V control on the two predominant energy saving control strategies for outdoor lighting: a Part-Night Dimming (PND) strategy that dims light output for part of the night and a Constant Light Output (CLO) strategy that trims excess initial light output and subsequently compensates for lumen depreciation over luminaire lifetime.
Cumulative energy and cost savings delivered by dimming curves from all luminaires characterized in this study, for one PND strategy (red) and two CLO strategies—L90 at 20 years (green), L80 at 16 years (violet)—relative to the full rated power baseline. The gray shaded columns represent ANSI C137.1-2022 noncompliant products. Notably, L-3, L-9, and L-23 are three units of the same make/model streetlight.
The PND strategy should deliver an annual energy and cost savings of 18%, but comparison of expected savings vs. actual savings in PNNL’s study revealed an average reduction of only 12%. Similarly, the evaluation of two CLO strategies—L90 at 20 years and L80 at 16 years—showed, on average, an increase in energy use and cost of 2% and no savings, respectively, rather than the expected savings of 5% and 10%, respectively.
The use of ANSI C137.1-2022 compliant LED drivers is not a sufficient substitute for calibrating luminaire controller output to the actual 0-10V dimming curve of a given make/model luminaire. On average, ANSI C137.1-2022 compliant LED drivers do not improve the energy or cost savings delivered by a PND strategy, only marginally improve the savings delivered by an L90 at 20 years CLO strategy, and only improve the savings delivered by the L80 at 16 years CLO strategy from 0% to 5%—half of the expected 10% savings.
Download the study for complete results and recommendations here.
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