In this paper, an energy efficient streetlight for pedestrian roads is introduced. Energy efficiency is achieved via up-to-date light-emitting diode (LED) technology and added intelligence utilising integrated sensors and wireless control. Thermal and electrical design of the luminaire contributed to good technical functionality. The performance of the luminaire was validated with testing. The luminaire was compared with commercial lamp and LED-based street lighting technology by technical values and user acceptance. Energy savings of 19-44% through improved luminous efficacy was demonstrated without added intelligence. With smart control further power saving potential of 40-60% was shown depending on the lighting environment and pedestrian presence. User feedback of a pilot installation comparing commercial luminaires with the newly developed streetlight revealed that on average the users preferred the developed streetlight over the commercial luminaires.

Novel continuous and mass customizable lightemitting diode (LED) lighting foil system, capable to produce adequate lighting levels for general lighting, was designed, processed, and characterized. Lighting element substrate was processed by roll-to-roll (R2R) printing using silver ink and automatic bonding of LEDs and current regulators on polyethylene terephthalate (PET) substrate using isotropic conductive adhesive (ICA). Demonstrator consisting of two basic lighting elements contained 98 LEDs and produced 860 lm when running with 25 mA operational current through the LEDs when using total electrical driving power of 8.4 W. Measured power conversion efficiency of the demonstrator was 31 % and efficacy 102 lm/W. Element produced 460 lx illumination level measured by an illumination level meter at element's central axis at distance of 1 m. At a distance of 2 m, illumination level was 110 lx, respectively. Temperature measurements with T3Ster thermal characterization instrument showed that when driving LED with maximum nominal driving current of 100 mA, LED junction temperature was about 120°C, when lighting element was in air in room temperature. Accelerated environmental stress tests consisting of 500 cycles from −40 … +80°C in aging oven and 1000 h in +60°C/95 % RH climate chamber were performed to test samples without any failures. In addition, over 700 bending cycles using 20 mm bending radius were performed to test samples without any failures, so bonding of LEDs were shown reliable according to these tests. Achieved results proved that thin, flexible, and large area high luminous flux lighting elements and systems can be processed based on plastic foil manufactured using R2R silver ink printing and R2R automatic bonding of LEDs and regulator components using ICA on that foil.

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To improve thermal performance of high-power chipon-board multichip LED module, a copper-core metal core printed circuit board (MCPCB) substrate with copper filled microvias is introduced. As a reference, the performance is compared with alumina module with the same layout by means of thermal simulations and measurements. Up to 55% reduction in the thermal resistance from the LED source to the bottom of the substrate is demonstrated. The excellent performance of the Cu MCPCB module is due to copper-filled microvias under the blue LED chips that occupy the majority of the multichip module. The conclusion was verified by measuring increased thermal resistances of red chips without thermal vias on the Cu MCPCB module. However, as the blue LEDs dominate the thermal power of the module, they also dominate the module thermal resistance. The thermal resistance was demonstrated to correspond with the number of vias as lower thermal resistance was measured on modules with larger number of vias. The Cu MCPCB was processed in standard PCB manufacturing and low cost material, FR4, was utilized for the electrical insulation. Thus, the solution is potentially cost-effective despite the higher cost of copper in comparison with aluminum that is the most commonly used MCPCB core material.

Evolution of lumens per watt efficacy has enabled exponential growth in light-emitting diode (LED) lighting applications. However, heat management is a major challenge for an LED module design due to the necessity to conduct heat away from the LED chip. Elevated chip temperatures cause adverse effects on LED performance, lifetime, and color. This paper compares the thermal performance of high-power LED modules made with two types of circuit boards: novel substrates based on insulated aluminum material systems (IAMSs) technology that inherently allows using thermal vias under the LEDs and traditional metal core printed circuit boards (MCPCBs) commonly used with high-power LED applications. IAMS is a thick-film insulation system developed for aluminum that cannot handle temperature higher than 660°C. The coefficient of thermal expansion of IAMS pastes is designed to match with aluminum, which minimizes any bowing. The thermal via underneath the LED enables excellent thermal performance. More than 7°C reduction in LED junction temperature at 700-mA drive current and 27% reduction in the total thermal resistance from the LED junction to the bottom of the substrate were demonstrated for the IAMS technology when compared with MCPCB. When considering only the thermal resistance of the substrate, reductions of around 70% and 50% were obtained. This versatile and low-cost material system has the potential to make LEDs even more attractive in lighting applications.