The US Department of Energy (DOE) has conducted a Gateway trial of tunable LED lighting in three Carrollton, TX classrooms, and teachers felt that the solid-state lighting (SSL) installation improved the educational environment. Interestingly, the school district has decided not to invest in tunable LEDs on a widespread basis at this point due to the cost premium relative to non-tunable LED lighting. However, the district did say it would reevaluate tunable technology as more data becomes available documenting positive impacts in student learning outcomes and teacher satisfaction directly attributable to tunable lighting. And the report lacks quantifiable detail on aspects such as productivity improvement that have been associated with so-called human-centric lighting (HCL).

Interested in articles & announcements on tunable lighting?

The Gateway project took place in the Carrollton-Farmers Branch Independent School District (CFB). As with all DOE Gateway projects, commercially available LED lighting products were installed for evaluation in a working setting. The SSL installation included one 5^th-grade math and science classroom, one 4^th-grade reading and language arts classroom, and one 8^th-grade science laboratory at three different CFB schools. In each of the schools, there was a very similar classroom nearby that was lit with legacy fluorescent lighting, and those classrooms served as a comparative reference case to the tunable lighting installations.

The SPD settings are shown for the Gateway-evaluated tunable lighting, clockwise from top left: 3000K/Reading (top left), 3500K/Testing (top right), 4200K/General (bottom right), and 5000K/Energy (bottom left). All luminaires were on at full light output when the photos were taken. (Photo credit: Acuity Brands.)

In the Texas schools, the DOE installed a control panel that supported four scenes and separately four different spectral power distribution (SPD) settings — General (4200K CCT), Reading (3000K), Testing (3500K), and Energy (5000K). The scenes included:

• Full — all luminaires on at 100%
• AV Mode — the luminaire near the front of the room off and others set to 40%
• Presentation Mode — the luminaires near the front at 100% and others at 50%
• Dim — All luminaires at 10%

Other controls provided overrides. For instance, an up arrow allows the teacher to raise light levels at every luminaire by 5% each time the button is depressed and a down arrow works similarly to reduce light levels. Occupancy sensors can also turn the lighting off.

The full DOE report provides intricate details on photometric data gathered under the lighting. And it compares that data with the fluorescent reference classrooms. Generally, the LED system delivered higher-quality lighting, although there are some interesting details that the DOE discussed in new human response metrics that it studied in the classrooms. You can find the full report on the DOE SSL website.

But the summarized results are more focused on energy savings and whether the tunable lighting improved the educational environment. The energy efficiency angle is documented by facts, whereas the benefits of the lighting are generally limited to input from the teachers.

One of the teachers, who had suffered migraine headaches on a regular basis, reported no recurrence of migraines under the LED lighting. The report speculates that flicker from the fluorescent lighting may have been the culprit.

Generally, the teachers felt that the tunable system empowered them to provide a better educational environment. But the DOE noted that the empowerment is impossible to quantify. Overall, the teachers reported using the scene controls far more often that the SPD controls.

In almost all cases, the teachers used the dimming controls via scenes or manual overrides throughout the day. The combination of energy-efficient LED sources and dimming that wasn’t easily accomplished with the fluorescent systems resulted in the LED lit rooms using 58% of the energy used in the fluorescent-lit rooms.

The school district, however, balked at installing a tunable system on a more widespread basis after learning that the tunable system cost 25% more than an SSL system that just included dimming with a similar control strategy. Indeed, the scenes as implemented in the Gateway system were simply based on dimming with the SPD tuning handled separately, so a non-tunable system could deliver those scenes and perhaps better energy efficiency since tunable lights mix output from multiple LED channels.

The report implies that more training for the teachers in terms of lighting science could improve the way the lighting was used. For instance, the report says the teachers would only select among the General, Reading, Testing, and Energy SPD modes when those words literally described an activity at hand. Mostly the teachers left the SPD control on General and did not attempt to decide when other settings might be appropriate for an activity.

The DOE has published Gateway reports on numerous indoor lighting projects. For example, we reported earlier this year on a report focused on light quality in a variety of indoor settings. We also recently covered a Gateway report on OLED lighting in an office. But the industry sorely needs more data in settings such as the school where human-centric lighting or lighting for health and wellbeing concepts can be put to the test.

<Source : LEDS Magazine