by Brianna Crandall — August 8, 2019 — For facilities managers (FMs) who have wondered whether tunable LED lighting would be beneficial for the energy efficiency of their buildings and health and performance of their occupants, the final results are in for a US Department of Energy (DOE) GATEWAY evaluation of a trial installation of tunable-white LED lighting systems in three classrooms at an elementary school in Folsom, California.
Pacific Northwest National Laboratory (PNNL) evaluated the energy and photometric performance of the adaptive systems at the school to explore energy-saving potential. The evaluation found that if both systems are operated at full output, the light-emitting diode (LED) system would provide 46% annual energy savings over the incumbent fluorescent system, while producing similar illuminances.
DOE explains “tunable LED lighting” on its website. According to the site, there are three categories of color-tunable lighting: dim-to-warm, white-tunable, and full-color-tunable; only the white-tunable is discussed in this study.
The trial installation of the tunable LED lighting system was completed by Folsom Cordova Unified School District with the help of the Sacramento Municipal Utility District to understand both energy-savings potential and the potential to improve student health and academic performance, especially in children with autism spectrum disorder (ASD). The goal was to gain firsthand experience with tunable LED lighting in case future evidence confirms potential positive effects on student achievement.
According to DOE, tunable lighting systems offer the potential for significant energy savings relative to fluorescent systems and non-dimmable LED lighting systems. These savings are attributed to the higher efficacy of LED systems versus comparable fluorescent systems, and the dimming capability provided by tunable lighting — with additional energy savings possible in schools where illuminances exceed Illuminating Engineering Society (IES) recommendations.
Tunable LED lighting trial
The tunable LED lighting system was installed in August 2017, just before the start of the Folsom School District’s school year. One of the three classrooms was used for general-education fifth graders, and the other two for autism spectrum disorder (ASD) students. In each classroom, existing two-lamp T8 fluorescent recessed luminaires were replaced with recessed 2′ x 2′ white-tunable LED luminaires, and one 12′ white-tunable LED wall wash surface-mounted luminaire was installed above the whiteboard.
Image (left) and reflected ceiling plan (right) of classrooms L1 and L2 with the installed LED lighting system. Image courtesy DOE. Click image to enlarge.
LIghting system manufacturer Finelite supplied the tunable LED classroom lighting system and controls, which had been developed with research and development support from a competitive funding opportunity from the DOE Building Technologies Office’s Solid-State Lighting Program.
A wall-mounted, touch-sensitive controller, which communicated with the luminaires via a DMX512 protocol, was installed next to the whiteboard, and offered five preset scenes that could be altered with dimming (0%-100%) and color-tuning (2700 K to 6500K) slider bars, in addition to featuring on/off power buttons for the entire system and for the general and whiteboard luminaires separately.
Energy savings
Collection of energy data began during the last week of the 2016-2017 school year, while all three classrooms were operating under fluorescent lighting systems, and continued through the 2017-2018 school year. Based on the monitored energy use, the actual savings during a typical day ranged from 48% to 69%, depending on how the teacher used the controls.
Lighting energy use for a 24-hour period in Classroom L2. Graphic courtesy DOE. Click image to enlarge.
However, the actual energy savings throughout an entire school year will be less than that, because the DMX-controlled driver in each LED luminaire has a small power draw when the system is turned off, without which there might be tradeoffs in control flexibility, number of controllers, or dimming depth, explains PNNL.
Additional benefits
The lighting system manufacturer provided extra hardware and software to log the teachers’ usage of the control touchpads. The resulting data revealed that each of the teachers interacted with the LED lighting system differently, and distinct patterns emerged with respect to how the controllers’ preset, intensity, and spectral power distribution buttons were used.
For example, those in the ASD classrooms utilized the preset buttons and customizable slider bars regularly, while the general-education teacher mainly used the default on/off functionality, and they weren’t comfortable with a combination of higher CCT and higher illuminance settings, using the color slider or making another preset selection whenever they pressed the “Energize” button (control settings of 5000 K and more than 500 lx illuminance).
The teachers viewed the preset lighting options as particularly beneficial because they were quick to implement, and noted that the presets were a way to get students’ attention or cue them to transition between certain activities. According to the teachers, the lights were more effective in getting students’ attention than any other method they had tried.
The teachers considered the lighting system’s dimmability to be particularly valuable, with color-tunability seen as a secondary benefit. The individual differences between teachers in their use of controls showed the opportunity that tunable LED lighting systems can provide for customizing the educational setting.
PNNL concludes that the trial LED lighting installation at FCUSD not only offered significant energy savings compared to the incumbent fluorescent system but ultimately provided teachers with an additional tool for facilitating classroom activities. The implementation of the lighting system varied between classrooms, but the teachers included in this study agreed that the LED lighting system offered an improved working environment for themselves and the students.
GATEWAY conducts field evaluations of high-performance SSL products to collect empirical data and document experience with field installations. Real-world installations often reveal product limitations and application issues that are not apparent from laboratory testing, notes PNNL.
The Evaluating Tunable Lighting in Classrooms: Trial LED lighting systems in three classrooms in the Folsom Cordova Unified School District report is available for free download from the DOE website. DOE also offers information on understanding, specifying, controlling and testing LED color-tunable products.
