Solar street lights and other street light solutions using advanced solar technology

Research About the LED Lighting Over Legacy Lighting of the Solar Street Lights

As an energy saving product, the led lighting are get more popular than legacy (high pressure sodium) lighting. Recently, the Lighting Research Center (LRC) conducted a research about the two different light systems of solar street lights.

DELTA compared the LED installation to a neighboring HPS (high-pressure sodium) installation in the same business park. The DELTA study sought to quantitatively measure system performance, photometric performance, energy savings, and light pollution. Plus DELTA used volunteers to evaluate the LED lights.

Photometric performance

DELTA measured horizontal illuminances on the ground after about on years of the operation at the same location where visitors evaluated the LED installation. DELTA measured an average horizontal illuminance of 0.4 footcandle (fc) and an average-to-mininum uniformity ratio of 6:1. Therefore, the installation meets the relevant industry recommendations after a year of operation, but will eventually drop below the minimum as lumen degradation occurs.

Because of greater human sensitivity to light with a “white” appearance than a “yellowish” appearance at these illuminances, it is possible to predict improved visual effectiveness using “unified luminance” calculation. DELTA used the photometric information above to calculate unified luminance. DELTA estimates that the unified luminance of the system is approximately twice that of a high pressure sodium system at an equivalent photopic illuminance. But at higher illuminance, the advantage of this LED light source would be reduced.

Energy savings

The LED lights, at 79W per luminaire, use 38% less power than the HPS system. DELTA relied on Lighting Analysts' software to calculate illuminance along several hundred feet of roadway and found that the HPS system trailed the LED system in uniformity.

Light pollution

DELTA used the Outdoor Site-Lighting Performance (OSP) light pollution calculation techniques (developed by LRC) to compare the two installations. The LED installation did prove superior in terms of creating less light pollution. But the DELTA researchers attributed the difference more to the fact that the HPS installation was brighter than required than to the ability of LED luminaries to better control light within the test site.

Human Evaluation

For the human evaluation, DELTA recruited 26 volunteers to visit the field site after dark in September 2009. The participants completed a survey based on their visit with questions ranging from how safe the participants felt in the area to the ability of the participants to recognize friends in the light. Comparing the lights at a high level, 44% rated the LED and HPS lights the same, while 40% rated the LED lights superior.

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