2014 IES Street and Area Lighting Conference
September 14-17, 2014 | Nashville, TN
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The topics of this paper are mesopic dimensioning, glare properties and energy efficiency of LED street lighting. Road lighting luminance measurements and threshold increment (TI) measurements are made for four different LED street lighting installations. The effect of mesopic dimensioning on energy consumption and life cycle costs of the LED installations are examined. Through the calculations and measurements, the energy efficiency and glare properties of the LED installations are analyzed. The measurement results indicate that the measured and calculated threshold increment values differ from each other due to varying calculation parameters in real installations. It also shows that energy can be saved when mesopic dimensioning is applied to street lighting design.
The Backlight-Uplight-Glare (BUG) rating system has been proposed as a metric for evaluating luminaire photometric output with respect to issues surrounding exterior environmental sensitivity based on the Luminaire Classification System (LCS) infrastructure established in IES TM-15–07. The BUG rating system was adopted and issued as Addendum A to IES TM-15–07. The proposed original values for the BUG system have since been modified to decouple the uplight and glare ratings based on feedback received during the public review process, but the basic infrastructure of the BUG system remains unchanged. The results of the analysis examining the impact of decoupling on the BUG ratings of various luminaires showed that the vast majority, 78 percent of ‘U’ ratings, 90 percent of ‘G’ ratings and 94 percent of combined ‘UG’ ratings, will remain the same.
Daylight responsive dimming systems continuously adjust electric lighting output with an algorithm to maintain target illuminance levels at the workplane in combination with available daylight. A key factor of closed-loop proportional control algorithms is the ratio of photosensor response to daylight illuminance at the workplane. This ratio determines in part the control slope (M) between dimming level and lighting output. Although this ratio is known to vary significantly with sun and sky conditions, it is typically set to a fixed value at the time of calibration. Such practice adversely affects the accuracy and therefore reliability of these systems. To investigate how to improve performance, a solstice-to-solstice experiment was conducted in a conventional private office mockup with a large-area, south-facing window and a fixed height roller shade positioned to block direct sun for most hours of the year. This simple preliminary case was used to explore and define the methods for derivation of improved control algorithms with the intent of studying more complex cases in future work. First, variations in the ratio of photosensor signal to daylight workplane illuminance were analyzed using a divided time period, clearness index (KT) ratio, and the ratio of diffuse solar irradiance to global solar irradiance on an exterior horizontal surface (Id/IT). Second, an improved closed-loop proportional control algorithm was suggested based on least square fits to the experimental data assuming that commissioning would occur at targeted times. The performance of this improved algorithm was compared to a modified conventional control algorithm and found to deliver more reliable, accurate performance when commissioning was performed on two targeted days within the solstice-to-solstice period.
This study evaluated the energy impacts and cost differences of multiple lighting control strategies for a controls-only retrofit of a theoretical 1970’s or 1980’s office building, analyzed in Boston and Los Angeles. The minimum control requirements of ASHRAE 90.1–2007 established an energy baseline, and six control systems were assessed. Life-cycle costs were evaluated using equipment and installation cost estimates, provided by an independent contractor, and commissioning cost estimates, provided by an independent commissioning agent. Results suggest that advanced systems can achieve nearly 50 percent energy savings compared to code-compliant controls, and that the approach to space-planning can significantly influence the lighting energy density. The cost analysis shows that wireless lighting controls required lower investment to achieve a high level of functionality for retrofit applications. The cost of commissioning was found to generally be offset by the utility rebates available in both locations. This all combines to illustrate that advanced networked lighting control systems can lead to a lower lifetime cost of ownership compared to more traditional systems.