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Publications within the project


Subjective preferences and colour quality metrics of LED light sources. Dangol R., Lighting Research and Technology, published online in February 2013.

Investigation of user preferences for LED lighting in terms of light spectrum. Islam M., Lighting Research and Technology, published online in January 2013.

User acceptance studies for LED office lighting: lamp spectrum, spatial brightness and illuminance level. Islam M., Lighting Research and Technology, submitted in June 2013.

User acceptance studies for LED office lighting: visual apperance, comfort, attractiveness and preference. Dangol R., Lighting Research and Technology, submitted in June 2013.

Spectrally tuneable LED Lighting Simulator Laboratory Room at University of Pannonia. Szabo F., Przeglad Elektroniczny, submitted in June 2013.

Optimization of LED spectra based on user preferences. Baniya RR., Lighting Research and Technology, submitted in June 2013.

New approach for the estimation of the flow velocity generated by acoustic streaming actuators. Klein J., Löschke J., Mitic G., Honsberg-Riedl M., Vontz T., Mock R., conference Proceedings Actuator 2012 in Bremen, Germany, June 18-20, 2012.

Primary optics for efficient high-brightness LED color mixing. Cvetcovic A. et al (LPI), SPIE conference Optics and Photonics in San Diego, August 12-16, 2012.

Brightness perception. Vidovszky-Nemeth

, A., Schanda J. (UPAN), CIE Lighting Quality & Energy Efficiency, Hangzhou, China, September 19-21, 2012.

Noiseless cooling by ultrasonic streaming in resonant mode. Knoche, T., Reinhart, G., Honsberg-Riedl, M., Mitic, G. (Siemens), submitted to Journal of Thermal Science and Engineering Applications.

Subjective preferences and colour quality metrics of LED light sources. Dangol, R. et al (Aalto), accepted for publication in Lighting, Research & Technology.

Investigation of user preferences for LED lighting in terms of light spectrum. Islam, M. et al (Aalto), submitted with referee feedback considered to Lighting, Research & Technogy.

Full-ceramic converters for warm-white LED. Pricha, I. (Siemens), JuniorEuroMat2012, Lausanne, July 23-27, 2012.

Correlation between subjective preferences and colour quality descriptors for LED lighting. Dangol, R. et al (Aalto), 11th L&CV Symposium.

Phosphor Ceramics for Solid State Lighting. Pohl, B. et al (Osram), International Symposium of Luminescent Materials, Hsinchu November 15-17, 2012.

Properties of high quality LED shop illumination - acceptance studies. Wilm, A. (Osram OS), 10. VDI-Fachtagung 'Innovative Beleuchtung mit LED', November 8-9, 2012

Inhomogeneous source uniformization using a shell mixer Köhler integrator. Chaves, J. et al (LPI). Invited paper in SPIE Optical System Design, Barcelona November 26-29, 2012.

Spectrally Tuneable LED Lighting Simulator Laboratory Room at University of Pannonia. Csuti, P. et al (UPAN), Submitted to SPIE Press Room.

Improved color matching functions for better visual matching of LED sources. Csuti P, Schanda J, Petluri R, McGroddy K, Harbers G. CIE 27th Session, Sun City, ZA. 2011.

Abstract: It is common in lighting installations for colour differences to be observed between luminaires using LED sources and those using traditional light sources such as Tungsten-Halogen. These differences can in most cases be confirmed by measuring the chromaticity coordinates, but we found that they can also be caused by failing of the CIE 1931 colour matching functions (CMFs), in particular with LED sources with a relative high blue peak, which is the subject of this paper. For this purpose, visual matching experiments were performed to evaluate the CIE 2° and 10° standard observer CMFs, the tentative 2° and 10° CMFs under discussion in TC 1-36 [1], and a modified set of 2° CMFs developed at the University of Pannonia.

A new method for investigating colour harmony distortion of light sources. F. Szabó, G. Sárvári, K. Toth, L. Balazs, J. Schanda A. 27th CIE Session, 2011, Sun City, South Africa.

Abstract: The failure of the current CIE Colour Rendering Index1 (CRI) for modern (especially LED based) light sources is anecdotal. CIE TC1-62 recommended the development of a new colour rendering index or more indices to make an improved description of light source colour quality2. One of the authors previously developed new colour harmony models based on visual experiments3. Based on these new models of colour harmony, a Colour Harmony Rendering Index (Rhr) was introduced4 to describe the colour harmony rendering property of light sources as a new colour quality metric. Until now, this metric is the only one, which deals with the colour harmony rendering property of light sources. A need of the demonstration of colour harmony rendering phenomenon was raised by lamp designers and manufacturers as well as end-users, to get familiar with this new quantity. During this workshop presentation, a newly developed computer software will be introduced.

User Acceptance Studies for LED Lighting in Offices. Dangol R, Islam M, Bhusal P, Halonen L. Poster at Aalto Energy Day 2011.                                                             

Abstract: The LED based lighting technology is growing rapidly and improving day by day. The technology is more energy efficient and ergonomic.  With LEDs it would be possible to concentrate light on actual working areas as well as adapt light colour for different activities such as alertness, which in turn can affect circadian rhythm positively. However, the colour rendering property of LED light source is an arguable and questionable fact. The presently used colour quality descriptor of light source [CIE Colour Rendering Index (CRI)] is out-dated and does not describe colour quality of LED correctly. For the tuneable light spectrum and dynamic light levels provided by LED lighting, more diversified description of lamp light quality will be required in the future. Highly energy efficient, long lasting lamps with reasonable price will not be well accepted by the end-users if the colour quality of the lamp is poor. Accurate assessments and evaluations of colour quality are critically important for LED lighting technology. Therefore, Lighting Unit, Department of electronics is currently working on user acceptance studies for energy efficient office lighting with LEDs. The user acceptance studies are divided into two parts: small scale booth experiment, and full scale experiment.

Ceramic processing of multi-phosphor converters for solid state lighting. Pricha I, Liepold U,  Ahlstedt M, Pohl B, Kechele J,  Moosburger J, Göötz B. 10th International Symposium on Ceramic Materials and Components for Energy and Environmental Applications, May 20-23, 2012, Dresden, Germany.    

Abstract:  For white and broad band emitting LEDs used for solid state lighting, ceramic converters exhibit several advantages over phosphor particles incorporated into optical resins, such as heat dissipation, efficiency and colour homogeneity. Nevertheless their processing is more sophisticated than for converters based on resin incorporated phosphor particles, especially if a composition of different phosphor systems is required. Particularly challenging is the combination of oxide and nitride based phosphors in ceramics, since the high temperatures for sintering usually induce severe chemical interactions, causing deterioration of the phosphors. As an approach for the minimization of the interface between two phosphors, layered ceramic composites can be used. However interaction can occur in the contact region between layers of different phosphors. Moreover, differences in the sintering behaviour of the two materials can cause delamination or crack formation within composite layers. The influence of processing parameters, especially the sintering temperature, on the luminescence and the ceramic properties of single phosphors and multi-phosphor materials therefore had to be investigated. Under mild thermal conditions during sintering chemical reaction is significantly reduced, however, it usually yields a low ceramic density, resulting in poor conversion efficiency due to strong light scattering. To achieve a good compromise between ceramic quality and temperature load, different ways for layer composite formation and processing were studied. Amongst others, the feasibility of interlayers was investigated as well as their effect on layer adhesion or inhibition of interaction between the phosphors. The investigations are conducted as a part of the EU-funded project SSL4EU (FP7-257550).

Phosphor converters for LEDs - Overview on basics and own developments. Pricha I. Tutorial, November 25, 2011, Bayreuth, Germany.

Abstract: The first part of the presentation focuses on luminescence theory. It gives an introduction to general aspects of luminescent materials, consisting of doped inorganic insulator materials, and their functionality using general excitation and emission models. A short overview of light emitting diodes (general design and functionality) and lighting technology (colour point and CIE colour diagram) is given. The state-of-the-art for white LEDs in lighting applications and challenges (e.g. heat dissipation) are considered, motivating the need for new innovation approaches using a fully ceramic converter. The fabrication of multilayer ceramics is summarized, as well as the use of multilayered ceramics to minimize system interfaces in order to reduce interactions between different phosphor systems. A short generalized insight to first results during of the converter development using multiphosphor layers is given. Tape-based ceramic processing is explained first. Within the process flow, challenges and relevant process parameters are discussed for each step using general monophosphor processing as an example. Possibilities for ceramic multilayer production, e.g. lamination, slurry coating, sedimentation are shown schematically and briefly discussed and compared. The luminescence spectra of the first sintered single and multiphosphor ceramics are investigated as a function of the sintering temperature. The maintainance of phosphor functionality within the composite material is demonstrated with emission band fitting.

Other publications by the partners on project-related topics


Colour vision and colour rendering

Testing Colour Sample Datasets for Calculating Colour Rendering Indices. F Szabó. Kosztyán T, Schanda J. CIE Symposium, Ghent, 2010.

Abstract: The aim of this study is to investigate test sample dependence of the current CIE colour rendering index (CRI) calculation method[1]. Authors of this study calculated colour rendering indices of 9 test SPDs with different test colour sample sets. 8 and 14 test colour samples from Ra method, 15 samples from CQS and 215 samples from Philips were applied as test colour samples. CRI values and ranking order of the 9 test light sources was compared in case of the different test colour sample sets.

A light source colour fidelity index for the graphic arts. Schanda J. IARGAI Conf., Budapest, 2011 Sept.

Colour Rendering Index and colour rendering of LEDs. Dangol, R. Master Thesis Aalto University, 2011.                                                                                          

Abstract: The purpose of this study was to understand CIE (Commission Internationale del´Eclairage) Colour Rendering Index (CRI) and its deficiencies. Another aim was to find out limitation of CIE CRI for LEDs. Finally, current works on colour rendering of LEDs was examined in the study. CIE (Commission Internationale de l´Eclairage) Colour Rendering Index (CRI) is the only internationally recognized colour rendering metric. This metric expresses the colour rendering properties of light sources based on colour shift of test objects when illuminated by reference illuminant and test source. The CIE method to obtain CRI is called CIE test colour (sample) method. Despite of prominence, CIE test colour method has numerous deficiencies. The problems of CIE test colour method became more serious when applied to white light emitting diode based sources. Various studies have indicated that even LEDs with low values of CIE CRI can produce visually appealing, vivid, and natural light. CIE technical committee TC1-62 concluded that the CIE CRI is generally not applicable to predict the colour rendering rank order of white LEDs light sources. The colour quality of light sources is not just a colour difference. Colour discrimination, colour harmony, colour preference, colour acceptability, visual clarity, and brightness are some known dimensions of light source colour quality. For different application different light sources are suitable and relevant dimensions of light source colour quality should be used to select appropriate light sources as per the application. The universal colour rendering metric should be able to define all the dimensions of light source colour quality.

Brightness, visual comfort and task performance
. Vidovszky-Németh Á, Schanda J.
CIE 27th Session, Sun City, ZA. 2011.                                                                                                                                 

Abstract: Brightness perception of near white surfaces is influenced by the spectral power distribution (SPD) of the illumination. At the same time this has an effect on task performance, either directly or via influencing the mood of the worker. With the introduction of modern SSL sources the SPD of illumination can be varied almost at will. Investigations were conducted to test the SPD dependence of the brightness perception of equal correlated colour temperature (CCT) white lights. Very big inter-observer variability was found. Parallel experiments are under way to test the CCT and spectrum dependence of task performance, conducting long duration (1 to 2 hours) proof-reading and visibility studies both using paper tasks and projection reading and computer input tasks. The lighting seems to have both a direct influence on task performance and via comfort perception.

A better description of metameric experience of LED clusters
. Csuti P, Schanda J, Light & Engng 18 44-50 2010.

Abstract: We carried out colour matching experiments using colour LED clusters and filtered incandescent lamps. There is considerable difference between the instrumentally determined chromaticities if broad band colours are visually matched with narrow band colours produced by additive mixture of the light of red, green and blue LEDs. The measured u’,v’ chromaticity difference could be halved if not the 2° standard colour matching functions (CMFs) are used, but CMFs derived from cone fundamentals. As a further step the cone fundamental derived CMFs have been modified. The obtained CMFs provide very good agreement between the visual and instrumental matches. These tentative CMFs have to be further evaluated with a larger number of observers, before it can be recommended for general practice.

Experimental modeling of colour harmony
. Szabó F, Bodrogi P, Schanda J. CR&A 35/1 34-49. 2010.

Abstract: This study investigates colour harmony in visual experiments in order to develop a new quantitative colour harmony model. Based on new experimental results, colour harmony formulae were developed to predict colour harmony from the CIECAM02 hue, chroma, and lightness correlates of the members of two- or three-colour combinations. In the experiments, observers were presented two- and three-colour combinations displayed on a well characterized CRT monitor in a dark room. Colour harmony was estimated visually on an 11 category scale from -5 (meaning completely disharmonious) to +5 (meaning completely harmonious), including 0 as the neutral colour harmony impression. From these results, mathematical models of colour harmony were developed. The visual results were also compared with classical colour harmony theories. Two supplementary experiments were also carried out: one of them tested the main principles of colour harmony with real Munsell colour chips, and another one compared the visual rating of the new models with existing colour harmony theories.

Do LEDs need  a new colorimetry?
Schanda J. British Colour Group Newton Lecture, 3 March 2010.

Optics and optical design

Free-form Fresnel RXI-RR Köhler design for high-concentration photovoltaics with spectrum-splitting.
M. Buljan, P. Benitez, R. Mohedano, J. C. Miñano, Proc. SPIE, San Diego (2011).

Progress on ultra-high efficiency, high-concentration pv system based on spectral division between a gainp/gainas/ge and bpc silicon cells. Mohedano R, Buljan M, Benítez P, Miñano J.C, Sun Y, Falicoff W, Vilaplana J, Chaves J, Biot G, López J, Proc. PVSEC Hamburgo 2011.

Spiral nonimaging optical designs. P. Zamora, P. Benitez, J. C. Miñano, J. Vilaplana, Proc. SPIE, San Diego (2011).

Novel free-form optical surface design with spiral symmetry.
P. Zamora, P. Benitez, J. C. Miñano, J. Vilaplana, , Proc. SPIE, San Diego (2011).

Spiral optical designs for nonimaging applications. P. Zamora, P. Benitez, J. C. Miñano, J. Vilaplana, M. Buljan, Proc. SPIE, Marsella (2011).

Progress In Fresnel-Köhler Concentrators. Mohedanoa R, Cvetkovića A, Benítez P, Chaves J, Miñano J.C, Zamora P, Hernandez M, Vilaplana J, CPV7 Las Vegas 2011.

Performance Modeling of Fresnel-Based CPV Systems: Effects of Deformations Under Real Operation Conditions. A.Cvetkovic, R.Mohedano, O.Gonzalez, P.Zamora, P.Benitez, P.M. Fernandez, A. Ibarreche, M.Hernandez, J.Chaves, J.C.Miñano CPV7 Las Vegas 2011.

Characterization of Fresnel-Köhler Concentrator. Cvetkovic, R.Mohedano et al. Proceedings of the 25th EU PVSEC/WCPEC-5, Valencia 2010.

Compared performance of fresnel-based concentrators at array level. Mohedano R, Cvetkovic A, Benítez P, Chaves J, Zamora P, MiñanoJ.C, Hernandez M, Buljan M, Proceedings of the 25th EU PVSEC/WCPEC-5, Valencia 2010.


LEDs and energy-efficiency


LED module design and testing. Tetri E, Paakkinen M, Halonen L.
CIE 27th Session, Sun City, ZA. 2011.

Abstract: Twenty-two different modules were burnt 6000 hours in controlled circumstances in life test racks. In the modules were used different LEDs from different manufacturers, but also different substrates and optical lens materials. Photometric and electrical values were measured during burning hours. Results of the life test showed that the LED´s junction temperature is the key issue when designing module or luminaire. The junction temperature has an effect on luminous flux, lumen maintenance and thus also life time of LED module or luminaire. The temperature had an effect also on the lens material.

Lighting control and energy-efficient lighting. Halonen L, Tetri E. Lighting India, July-August 2011, 28-32.

Energy-efficiency demands and current changes in the lighting field. Halonen L. IODS, Sept 27-28, 2010, Saint Petersburg/Russia.