Swiss Photonics Workshop on Intelligent Efficient Solid State Lighting

Around 100 specialist, members and interested parties accepted the invitation and attended what turned out to be a very informative workshop. Because this was a follow-up event to the Large- Area SSL workshop held in Lausanne in 2015, the main focus of the morning was on the LASSIE project. In the afternoon, however, information on the more general and extensive topics of HCL and IoT was provided. Renowned speakers from the DACH region (Germany, Austria and Switzerland), as well as experts from The Netherlands, Finland, Sweden, Belgium, France and Spain all shared their knowledge with the attendees.

A Warm Welcome

Dr. Christian Bosshard opened the workshop with a short welcome and an introduction to Swiss Photonics, after which, Dr. Christoph Kloepper briefly introduced the Basel area in respect to technological and innovative power. He explained that Switzerland, in general, and the Basel area in particular, have the highest innovation indices in various international innovation reports. It isn’t a coincidence that CSEM, which is located in Muttenz, coordinated the LASSIE project and substantially contributed to the outcome of the project.

Large Area Intelligent Efficient SSL - Focus on the LASSIE-FP7 Project

Dr. Rolando Ferrini introduced the audience to the topic and the objectives of the LASSIE project before divulging details, results and technologies of the Large Area Intelligent Efficient SSL project. Large area lights are an extensively used product in commercial lighting applications. While conventional troffers already do quite a good job, modern technology could do it even better with some additional, integrated features. However, before the project kicked off, costs for high quality solutions were quite high and the true potential of modern technologies wasn’t being utilized by far. At that time, although OLEDs were a very good candidate for this type of lighting, they weren’t price competitive, and still aren’t. There are also other challenges like beam shaping. On the other hand, LEDs were still costly and had their own disadvantages. The challenge that had to be overcome was to find a concept for a thin fixture that would offer high light quality and color, or at least CCT tuneability, at a reasonable price, while having a small environmental footprint. Dr. Ferrini gave a short overview of the key technologies that were used in the final concept and summarized the major achievements, which include a high CRI above 90 with high color accuracy within 3 to 1 step MacAdam ellipsis and constant color over time due to an intelligent sensor feedback loop.

Comparison between the LM stack that was developed in the LASSIE project and a pure diffuser foil on a thin area light

Senior project leader, Oscar Fernández talked about the optical requirements and solution for the project. For those that attended his talk at the LpS in Bregenz, this was a repeat, but a good opportunity to refresh one’s memory. First he made a quick comparison of expensive OLED lights and LED solutions. It was shown that glare is a much bigger issue with LEDs. But there are two very different concepts possible for LED area lights - both with advantages and disadvantages. Edge lit LED luminaires are a thin but heavy option. They provide moderate light uniformity, lower efficiency and a large color shift across the emitting area. Conventional, direct-lit luminaires are lighter and more efficient but either add volume to the luminaire because of the greater distance needed between the LEDs and the diffuser, or they produce undesired multi-shadows. To avoid or reduce that, the Lambertian emission needs to be changed into cosine-cubed batwing light distribution. This is usually done with bulky and heavy “macro” lenses that add volume and costs to the system. Thin films for free form structures could be an alternative solution but must be tailored with a large degree of freedom in mind. The proposed solution: periodic microstructures, and especially “micro-structured pixel”, are a much simpler solution. These can be cost effective, roll-to-roll processed foils that help to reduce the number of LEDs needed. Such foils are already in use as light enhancement foils in LED displays. Using two rectangular foils in position with a diffusor, leads to the desired result: a flat, thin, highly efficient and cost-competitive area light where variations and further adaptations are possible. While a color tunable multi-LED solution significantly increases the cost, low CRI LEDs can be used with a down-converting phosphor sheet resulting in a high CRI solution with a reduced cost.

Demonstrator and development board for Fraunhofer’s integrated sensor using plasmonic filters

Dr. Stephan Junger from the Fraunhofer Institute presented a new CMOS technology based sensor concept that helps to add intelligence to color tunable luminaires at reasonable costs. While conventional sensors are usually designed with some type of pigment filter or interference filters and are restricted to RGB or, rarely, RGBW, this concept is different. It uses a nano structured metal layer as a so-called plasmonic filter. This technology allows designing a photodiode array of 12 channels between 400 and 700 nm in a 5x5 mm package. The LASSIE project was ideal to prove the concept and test the accuracy of the approach. It also helped find out how many different channels are really needed to provide high accuracy at optimized costs. Fraunhofer found that this technology could provide sensors with a cost target of €1 in high volume. Compared to that sensors with similar functionality are currently not available below €2.

VTT is a research institute in Finland with a lot of experience in R2R manufacturing processes and flexible substrates. Senior Scientist, Dr. Kimmo Keraenen, described their role and tasks within the project. One key issue, as is very often the case, was thermal management. They compared different technologies, rigid and flexible, and finally found a suitable solution for their printed R2R technology that led to excellent results for this application. A PET substrate was perforated using a USHIO mechanical puncher and wafer diced ceramic/metallic foil pieces were bonded to these vias. Circuit wiring and contact areas were printed with silver ink. While the cool white LEDs were bonded on pads with the heat management structures below, the color LEDs were bonded on contact pads without heat management structures. Necessary wire crossings were enabled by zero Ohm resistors.

Leire Barruetabeña from the Spanish specialist for environmental management and life-cycle assessment, Gaiker, explained that new regulations and economic efficiency require having a life cycle assessment in mind from the beginning of a project. According to her findings, an efficient design is still key for an environmentally friendly and cost-effective solution. 85% of CO2 is generated during the use-phase of an LED product. Therefore better efficiency has the greatest impact. The major cost driver is still the LED package, respectively, the number of used packages. More efficient LEDs can reduce cost and simplify design owing to a reduced number of LEDs.

Dr. Adrian von Mühlenen, representing the Technology Incubator of BASF Switzerland in Basel, showed an interesting approach to down-convert white light of low CRI to generate a high CRI white light. The R2R manufacturing based technology is still in a research state and therefore just basic information and preliminary results could be disclosed at the workshop. A strategic decision if and when the technology will be transformed in a standard product, still needs to be made.

Christian Hochfilzer, Technical Director at Regent, emphasized that technology is no longer the main driving force behind the lighting evolution. He demonstrated that intelligence and system integration are relevant success factors. Contemporary lighting concepts need to be flexible, and IoT has an important role, providing new services. Dr. Hochfilzer identified IoT as being a complicated and critical strategic topic. The choice of the right technology from the bunch of competing approaches is especially crucial for small to mid-size companies to hold their own in the marketplace of the future.

The session was then completed with the talk of Peter Bennich, Senior policy adviser (at the Swedish Energy Agency); chair of the IEA 4E SSL annex. He explained the background, the goals and the activities. One of the challenges in reaching the goals is seen in the harmonization, recognition and acceptance of standards and regulations, worldwide. In a first step testing methods and results were compared. He also emphasized the reaction of the 4E on new circumstances. Smart lamps have a great impact on energy use and active functions often need more than pure standby energy. In some cases, these standby losses exceed active energy consumption of 3 hours.

Life Cycle Thinking has been recognized in the EU as the most suitable methodological framework for most product and process related sustainability discussions

Smart & Human Centric Lighting - Technologies, Bio-physiology and Application

EPIC’s Director General, Carlos Lee, chaired the session that was characterized by exciting discussions and Q&As. The session started with Exalos’ CTO, Markus Duelk, who gave a status report on the Superluminescent Light Emitting Diode (SLED) technology and prospects for future development and possible applications. In many aspects, visible light SLEDs are combinig the best of both technologies, LEDs and SSL lasers, but they also have their weaknesses. The major disadvantage is not being powerful enough for most lighting applications today. Improvements are possible, but will take time.

LETI’s LED and OLED technology and business expert, Hani Kanaan, talked about “Micro LED Matrix for Smart Lighting System and Automotive Headlamps Applications”. The technology distinguishes significantly from conventional LED technology. Currently, the smallest pixel size is 2 μm. Multi quantum well technology is used to generate different colors and could allow for color tuning applications. While being especially interesting for display technology, there might also be a certain potential for smart and human centric lighting applications.

Enno Langendijk from the TNO Holst Center presented the PI-SCALE project. Visitors of the LpS 2016 in Bregenz might already be familiar with the project that deals with establishing a pilot line for R2R production of flexible OLEDs. The aims of this project are to help speed up the transition from lab to commercialization for Europe’s lighting and OLED industry - bridging the gap.

Smart lamps may use more energy in standby mode than during the active phase

Beat Ruhstaller, Chairman at Fluxim and Professor at the Zurich University of Applied Sciences, talked about “Design, Characterization and Optimization of OLEDs for Lighting”. Using his research results, Professor Ruhstaller confirmed statements by Professor Kido that were discussed at the OLED track of LED Lighting Japan in 2014 (see LpR 42 Event Report: Lighting Japan - Strong Focus on OLEDs). Furthermore, he analyzed the different challenges from conductivity issues to light extraction to angular dependency of light color. He showed how manufacturers deal with these types of issues today. Regarding light outcoupling, he presented a highly accurate simulation model, compared the efficiency of an internal light extraction structure with an external light extraction structure and the combination of both. Using two rough interfaces increases the emitted lumens by a factor of 2.1.

While flexible OLEDs can be customized to virtually any shape and color, they are still facing technical challenges

The last part of the afternoon session focused on the different effects of light on humans. Professor Cajochen, who gave a presentation in a workshop at the LpS in Bregenz and whose findings were discussed in the TTB interview in LpR 58 - Nov/Dec 2016 issue, gave the audience the current status of this research discipline. He explained the circadian system and Melatonin rhythm in detail and presented alarming figures about smartphone use in adolescents (14-20 years) which is one of the most critical light sources with high melatonin suppressing light levels besides computer screens. Due to the distance, he feels that TVs don’t have such critical effects. He also showed that a lux level of 120 lux has acute alerting effects on humans. Declarative learning effects test results for correctly identified new word pairs were significantly better when LED screens were used while correctly identified old word pairs showed almost no difference between LED screens and non-LED screens. Professor Cajochen emphasized that light is not just for vision but has many non-visual biological effects on humans, some of which are still not fully understood. He asks that non-visual lighting solutions should be dynamic and individual; dynamic in respect to intensity and duration, spectral composition, and dynamic according the time of the day; individual depending on gender, age and chronotype.

Wilfried Pohl from Bartenbach reflected on the topic from the perspective of a lighting design company. He added technical questions and requirements to the medical requirements, and he showed a dynamic illumination of a hospital from a current research project. He identified some limitations and practical issues for successful implementation of dynamic and truly human centric lighting. The most important ones on a long list are costs, complexity, confusing user interface, limited interoperability.

Dr. Heinz Seyringer from the Zumtobel Group added the view of a lighting manufacturer to complete the picture. He started by showing the dynamism of daylight during the day in respect to CCT and intensity. He showed what is already available on the market and some effects of human centric lighting on learning efficiency. He also emphasized that more than 95% of our decisions are made unconsciously and can be affected by light. He suggested that a more holistic approach might be taken into account, including non-visible light to HCL, like UV-B that triggers vitamin D production. Finally, he presented the company’s thoughts about a more user-centric lighting achieved by intelligent, connected lights utilizing IoT and adding additional human centric services.

The use of smartphones in adolescents that might carry some health risks clearly shows how technology influences culture and behavior

Different light scenes for HCL in a hospital depending on the time of day and task

Final Thoughts

This small but excellent event was well organized. It targeted technicians, R & D departments, SMEs and LMEs as well as lighting designers, architects, and end-users like large retailers. The aim was to bring together these different groups and to present the final results from the LASSIE project and related topics. The well selected topics and speakers in conjunction with the welcome networking opportunities guaranteed that the event fully accomplished its purpose. In short, Muttenz was worth the journey. We are eager to see what is on the schedule for next year.