LED-research has been a focal point for the Fraunhofer-Institute for Applied Solid State Physics (IAF) since 1995. Researchers of the IAF developed the white luminescence LED, which is the foundation of the current LED-based lighting systems. This development led to the efficient LEDs becoming an excellent alternative to conventional lighting such as lightbulbs. There are however market access hurdles for LEDs that still exist today, including a comparatively high initial cost. Researchers of the IAF are inspecting these hurdles twofold: once on a more technical side and with a more interdisciplinary approach. The pilot project “SusLight” was created with the purpose of placing LED-technologies in new application fields and examining to what extent customer acceptance or political strategies influence the spread of the alternative technology.
Interdisciplinary Research as Part of the Sustainability Center Freiburg
As part of the Sustainability Center Freiburg (LZN), a collaboration between the Fraunhofer IAF and the University of Freiburg was initiated in 2014 in the form of the pilot project “SusLight: Sustainable LED Lighting – Technological Challenges, Barriers to Market Entry and Political Acceptance”. Various faculties of the University of Freiburg participated in the collaborative work: the Fritz-Hüttinger-Chair of Microelectronics from the Department of Microsystems Engineering (IMTEK), the Department of Economic Policy and Constitutional Economic Theory and the Department of Public and Non Profit Management. The experts of Hahn-Schickard also played a key role in the project, especially given their closeness to industry.
A network between the Fraunhofer IAF, the University of Freiburg and industrial partners had already been previously established. “We had a clear push from our director for an even stronger interdisciplinary collaboration. The timing was perfect when a networking workshop was offered shortly after by the LZN”, explains Dr. Michael Kunzer from IAF. Kunzer and his colleague, Andreas Zibold, had to laugh in response to the question, if the collaboration caused any problems. “We had to first have everyone speaking the same ‘language’ at our meetings.” The partners divided themselves into two thematically different groups: the first, a more technical group, dealt with the microelectronics and software of the project while the other, more social-science oriented team inspected behavioral and business aspects. Researchers from IAF and IMTEK examined the efficiency of modules and drivers based on Galliumnitrid (GaN).
Flicker-free and resource-efficient LED-Technology
The cooling of LED-systems is particularly important, since the efficiency of LEDs decreases with increasing temperature. Because of that, LEDs are fixed on thermally conductive plates such as ceramics like aluminum nitride or aluminum oxide and analyzed for changes in efficiency. In a separate project, IAF researchers worked on high frequency circuit transducers for the transformation of line voltage to direct current. Their aim was to ensure that the LEDs could operate flicker-free. Flickering can negatively influence human health and under certain circumstances, even lead to migraines or epileptic seizures. To ensure the flicker-free operation, a specific amount of energy is stored in coils and capacitors in the circuit transducers. If the transformation described above were to proceed more quickly, less storage area would be required. Thereby, the entire design would be more sustainable and smaller, which simplifies the integration of the complete system. In the SusLight project, GaN power semiconductors, which have a high switch frequency with low frequency losses, were implemented. The entire system became thereby more efficient.
Smart Lighting for Efficient Work
The researchers of Fraunhofer IAF and from Hahn-Schickard also worked on the sensor integration for Smart-Lighting-Technology. As Kunzer explains, humans have a “blue light sensor” in their eyes, along with rods and cones, which determines whether it is day or night. This sensor regulates our circadian rhythm via hormones. The larger the amount of blue light in an area, the more hormones are released to keep the body alert and awake. Logically, these hormones also indirectly influence our reaction capacity. If there is too little blue in the light, i.e. a too high color temperature, then that situation is not optimal for concentrated, alert work.
The LED-system developed during the SusLight project is able to imitate the natural continual color gradient of the sun, by using four different color channels between 2,000 and 2,700 Flux. Thanks to internal color sensors, lighting can be optimized and perfectly controlled for various activities from a working environment to a sleeping environment. This “Human-Centric-Lighting” process can determine exactly, what sort of lighting is needed in a room, and accordingly send out the appropriate flux. The system could even be so precise as to analyze, which percentage of a desk is in that moment being used and only illuminate that bit. This would lead to an increased saving of energy and a general increase of sustainability.
Market Acceptance of smart LED-Lighting
A further key research point of this project was the query, how the acceptance of LEDs as viable products for potential consumers could be increased. A group of behavioral scientists of the University of Freiburg concentrated on examining product attributes and which thereof are of interest for consumers. The group wanted to identify which characteristics of the LEDs such as dimming or the previously described “Human-Centric-Lighting” functions were considered important. The results showed that there are in fact, certain important characteristics including, a warm white color temperature, high energy efficiency and few emissions and pollutants. Less relevant were characteristics such as Smart-Home compatibility possibilities, dimming, and the country of manufacture.
The business researchers of the Public and Non-Profit Management Department of the University of Freiburg examined, what possible tactics could be used to increase the widespread use of LEDs. They wished to analyze, how one could “nudge” a consumer into buying LEDs instead of a lightbulb. The team made sure to take psychological aspects into consideration, such as the possible influence of pride or guilt feelings. Of course, the relatively high costs of LEDs is another contributing factor for consumers. “Yes, one has to spend 20 Euros as opposed to 2 Euros, but the higher costs are worth it in the long run. Besides, we can already see, that the prices of LEDs have dropped about 30% per year since 2014,” Kunzer explains.
The European Commission had promoted the step-wise ban of conventional lightbulbs in Europe via a directive for the eco-design requirements for non-directional household lamps in 2009. The reason behind this ban was the low efficiency of the lightbulb: only five percent of the required energy was used to produce light and the rest was lost as heat.
Such strict bans generally do not have the desired effect of influencing the buying behavior of the general public. However, the introduction of other influences such as a fitting tax-model or energy labels on the LEDs could promote the switch to buying the more expensive alternative. Such soft-paternalistic approaches were examined during the SusLight project by researchers of the Department of Economic Policy and Constitutional Economic Theory. Based upon their examinations, they were able to present a suitable strategy as a recommended action.
The work of the project partners culminated in a demonstrator. The team developed an exemplary Smart-Home in which four different rooms were set up, each with LED-modules and sensors, which control the color temperature and brightness. The developed hardware is comprised of integrated color, brightness and motion sensors. A highly efficient LED-Lighting-System was developed as a final demonstrator (see Figure 02), in which the color temperature between warm and cold white (i.e. between white light with a high blue light amount and a low blue light amount) can be manually switched by the user.
The LED: Efficient and Sustainable
A follow-up project and a multitude of new research questions were initiated by the work completed during this pilot project. Fraunhofer IAF researchers further examined the LEDs themselves for their dependability. There is often a discrepancy between the advertised number of usage hours and the actual lifetime of a LED. There are many factors which can decrease the vitality of a LED such as heat buildup, moisture, and corrosion or trace gas stresses caused by hydrogen sulfide. The effect of reduced light yield with time is caused, for example, by the penetration of moisture and gases in the system through poly-materials such as silicon or ceramics. At IAF, these exact degradation effects are examined as well as possible solutions.
As part of the sustainability aspect of LED-lighting comes the question of its recyclability. Specific parts of the system, such as the aluminum cooling element, are easily recycled. To what extent repairs of non-recyclable parts play a role in the extension of the lifetime of the systems is however an important research question. As Kunzer explains, this question can be analyzed threefold. “First, it is important to extend the lifetime of the LED-modules themselves. Secondly, their reliability needs to be increased. Finally, the availability of replacement parts needs to be guaranteed.” These aspects were exemplified with the possible scenario of street lamps. Multiple questions arose including whether a non-specialized technician would be able to switch out a defect lamp or would so-called “LED specialists” need to be hired? From where would replacement parts be obtained? In what way would the product cycle play a role? Such research questions are complex and the answer requires much time and effort.
With the completion of the project in September 2018, Dr. Kunzer, Mr. Zibold and their colleagues can proudly reflect on their work and results. As the colleagues describe it, the collaboration was not only successful but also a pleasant experience. Dr. Kunzer says, that the flexibility within the project led to an atmosphere in which the researchers were inspired to address a wide span of research questions, in order to reach their goals. A further collaboration between Fraunhofer IAF, the University Freiburg and other partners is already being planned. The colleagues are excited to further develop their ideas and to present new results in the future.