Browsing by Subject "Lighting"
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Item Open Access Accuracy limits of distance estimation in visible light systems with RGB LEDs(IEEE, 2019-09) Demirel, İlker; Gezici, SinanThe distance estimation problem is investigated for visible light positioning (VLP) systems with red-green-blue (RGB) light emitting diodes (LEDs). The accuracy limits on distance estimation are calculated in terms of the Cramér-Rao lower bounds (CRLBs) for three different scenarios. Scenario 1 and Scenario 2 correspond to synchronous and asynchronous systems, respectively, with known channel attenuation formulas at the receiver. In Scenario 3, a synchronous systems is considered but channel attenuation formulas are not known at the receiver. The derived CRLB expressions reveal the relations among the distance estimation accuracies in the considered scenarios and provide intuitive explanations for the benefits of using RGB LEDs.Item Open Access Color enrichment solids of spectrally pure colloidal quantum wells for wide color Span in displays(Wiley-VCH Verlag GmbH & Co. KGaA, 2022-07-18) Erdem, T.; Soran Erdem, Z.; Işık, Furkan; Shabani, Farzan; Yazici, A. F.; Mutlugün, E.; Gaponik, N.; Demir, H. V.Colloidal quantum wells (CQWs) are excellent candidates for lighting and display applications owing to their narrow emission linewidths (<30 nm). However, realizing their efficient and stable light-emitting solids remains a challenge. To address this problem, stable, efficient solids of CQWs incorporated into crystal matrices are shown. Green-emitting CdSe/CdS core/crown and red-emitting CdSe/CdS core/shell CQWs wrapped into these crystal solids are employed as proof-of-concept demonstrations of light-emitting diode (LED) integration targeting a wide color span in display backlighting. The quantum yield of the green- and red-emitting CQW-containing solids of sucrose reach ≈20% and ≈55%, respectively, while emission linewidths and peak wavelengths remain almost unaltered. Furthermore, sucrose matrix preserves ≈70% and ≈45% of the initial emission intensity of the green- and red-emitting CQWs after >60 h, respectively, which is ≈4× and ≈2× better than the drop-casted CQW films and reference (KCl) host. Color-converting LEDs of these green- and red-emitting CQWs in sucrose possess luminous efficiencies 122 and 189 lm W−1elect, respectively. With the liquid crystal display filters, this becomes 39 and 86 lm W−1elect, respectively, providing with a color gamut 25% broader than the National Television Standards Committee standard. These results prove that CQW solids enable efficient and stable color converters for display and lighting applications.Item Open Access Creating a coordinate database for the lighting of three dimensional art objects(Bilkent University, 2003) Dikel, Ekrem ErhanThis thesis proposes a Lighting Coordinates Database for the illumination of three-dimensional art objects. Finding and defining the weak points of current lighting methodology reinforces the importance of the need for such a database. The two methods of obtaining data for this database, the computer software and hardware method are described. For the case study, the head of Michelangelo’s David is chosen. By using the software method, the scanned image of David is illuminated and an example database is created. As the second method, a prototype of a lighting model, David’s scaled model is illuminated by using LED light sources and another example database is created.Item Open Access A critical analysis of sunlight patches in patient rooms via simulation(Taylor & Francis, 2008) Tanrıöver, S.; Düzgüneş, A.; Yilmazer, S.Recent research on patient recovery has indicated significant improvement in the conditions of patients treated in sunny rooms compared to those treated in shaded rooms. In this study, the amount of sunlight received in patient rooms with different orientations and opening positions was observed. Desktop Radiance 1.02 software was used to simulate the conditions in a typical double patient room. The area and location of sunlight patches on room surfaces were considered as analog indicators for the investigation. Seven orientations and three positions of standard window openings were studied on an hourly basis in different combinations at solstices and equinoxes from sunrise to sunset. Data were statistically analyzed for advantageous combinations of orientation and opening positions. Results indicated that rooms with right- and left-shifted openings receive direct sunlight more than rooms with centered openings, and these have sunlight mostly on walls, while those with centered openings have it mostly on floors. The study revealed that opening positions rather than orientation is crucial to the design of patient rooms regarding the penetration of sunlight. Orientation is effective only when the room surfaces are studied individually. The study enabled sun patches to be visualized in relation to patient beds, which is a significant determinant that can affect the location of the bed, and so patient in the room. The paper concludes with four proposals of an informal choice from these combinations that both admits sunlight and protects the patient from glare and excessive heat gain.Item Open Access Differences in illumination estimation in #thedress(Association for Research in Vision and Ophthalmology Inc., 2017) Toscani, M.; Gegenfurtner, K. R.; Doerschner, K.We investigated whether people who report different colors for #thedress do so because they have different assumptions about the illumination in #thedress scene. We introduced a spherical illumination probe (Koenderink, Pont, van Doorn, Kappers, & Todd, 2007) into the original photograph, placed in fore-, or background of the scene and-for each location-let observers manipulate the probe's chromaticity, intensity and the direction of the illumination. Their task was to adjust the probe such that it would appear as a white sphere in the scene. When the probe was located in the foreground, observers who reported the dress to be white (white perceivers) tended to produce bluer adjustments than observers who reported it as blue (blue perceivers). Blue perceivers tended to perceive the illumination as less chromatic. There were no differences in chromaticity settings between perceiver types for the probe placed in the background. Perceiver types also did not differ in their illumination intensity and direction estimates across probe locations. These results provide direct support for the idea that the ambiguity in the perceived color of the dress can be explained by the different assumptions that people have about the illumination chromaticity in the foreground of the scene. In a second experiment we explore the possibility that blue perceivers might overall be less sensitive to contextual cues, and measure white and blue perceivers' dress color matches and labels for manipulated versions of the original photo. Results indeed confirm that contextual cues predominantly affect white perceivers.Item Open Access Effects of coloured lighting on the perception of interior spaces(SAGE, 2015-02-01) Odabaşioğlu, S.; Olguntürk, N.Use of coloured lighting in interior spaces has become prevalent in recent years. Considerable importance is ascribed to coloured lighting in interior and lighting design. The effects of colour on the perception of interior spaces have been studied as surface colour; but here, the effects of three different types of chromatic light were investigated. The lighting differed in colour (red, green and white) and perceptions of interior space were assessed. 97 participants (59 women, 38 men; M age = 21.4 yr.) evaluated the experiment room on a questionnaire assessing eight evaluative factors: Pleasantness, Arousal, Aesthetics, Usefulness, Comfort, Spaciousness, Colour, and Lighting quality. Perceptions of the room differed by colour of lighting for some of the evaluative factors, but there was no sex difference in perceptions. Interior spaces may be perceived as equally pleasant under white, green and red lighting. Under white lighting a space is perceived as more useful, spacious, clear, and luminous. Green lighting would make the same effect. Green and white lighting were perceived equally comfortable in an interior space. Chromatic coloured lighting was perceived to be more aesthetic than white lighting. The results support previous findings for some evaluative factors, but differed for others.Item Open Access The Effects of correlated color temperature on sustained attention and mood of university students in learning environments(Bilkent University, 2015) Kocaoğlu, RenginThe aim of this study is to understand the effects of correlated color temperature on sustained attention and mood of university students in learning environments and to compare different color temperatures. The experiment was conducted with two different sample groups in two different lighting settings; 4000 K and 6500 K in a single phase. The participants were ninety seven undergraduate students from Bilkent University. The participants were seated in a regular lecture room and tested by the researcher. They were asked to perform three paper- based tests; one of them about the sustained attention, d2 Test of Attention, and the other two about mood, (PANAS) Positive and Negative Affect Schedule. It was found that correlated color temperature has no significant effect on concentration performance, errors of omission, total numbers of items processed. A certain conclusion could not be derived about the effect of color temperature on mood. However, color temperature has a significant effect on errors of commission and number of errors. It was found that 4000 K significantly increases errors of commission and number of errors, thus 6500 K is more appropriate for university learning environments.Item Open Access The effects of correlated color temperature on wayfinding : a study in a virtual airport environment(Bilkent University, 2013) Kumoğlu, ÖzgeThe aim of the study is to understand the effects of correlated color temperature on wayfinding performance in airports and to compare different color temperatures in order to understand their effects on wayfinding performance. The experiment was conducted with three different sample groups in three different lighting settings that are 3000 K, 6500 K and 12000 K. The participants were total ninety graduate students from twenty-one different departments of twenty-six different universities. The study was conducted in a single phase. The volunteered participants experienced the desktop VE one by one. The participants were seated at the computer and were tested by the researcher. They were asked to direct the researcher from the starting point to the final destination which was stated as gate numbered 109. It was found that correlated color temperature has no significant effect on wayfinding performance in terms of the time spent, the total number of error, the total number of decision points and the route choice during finding the route. However, the correlated color temperature has a significant effect on experiencing hesitations. It was found that the total number of hesitations decrease while the correlated color temperature increases from 3000 K to 12000 K.Item Open Access The effects of correlated colour temperature on wayfinding performance and emotional reactions(John Benjamins Publishing, 2018) Süzer, Özge K.; Olguntürk, Nilgün; MacDonald, L.; Biggam, C. P.; Paramei, G. V.This study investigated travellers’ wayfinding performance according to the correlated colour temperature (CCT) of lighting in a virtual airport environment. In the first phase an experiment was conducted under 3000K (yellowish-white) and 12000K (bluish-white) light. Universal face representations of basic emotions (anger, disgust, neutral, surprise, happiness, fear, sadness) were shown to participants and they were asked to choose a single face. In the second phase, two questionnaires were conducted to identify participants’ level of presence in the virtual environment. Females were significantly more lacking in confidence than males in finding their destination, hesitating more often. The results indicated that participants’ wayfinding performance was better under 12000K, which they also associated with more positive emotion.Item Open Access The effects of correlated colour temperature on wayfinding: a study in a virtual airport environment(Elsevier, 2018) Kumoğlu-Süzer, Özge; Olguntürk, Nilgün; Güvenç, DilekThis study was designed to explore the effects of lighting's correlated colour temperature (CCT) on wayfinding performance in airports and to compare different CCTs to understand their effects on wayfinding performance. The experiment was conducted in a single phase with the participation of three different groups of university students who experienced the virtual airport environment in three different lighting settings: 3000 K, 6500 K and 12,000 K. The participants were asked to direct the researcher from the starting point to the final destination. It was found that CCT has no significant effect on wayfinding performance in terms of time spent, total number of errors, total number of decision points or route choice. However, CCT does have a significant effect on hesitation; the number of hesitations decreased when CCT increased from 3000 K to 12,000 K. Gender difference was also explored regarding hesitations in this study.Item Open Access Effects of different lighting arrangements on space perception(Taylor & Francis, 1999) Manav, B.; Yener, C.The idea to improve the quality of lighting design in interior spaces has gained importance in the last years. This experimental study concentrateson the quality of lighting and the relation between lighting arrangements and perception. A room having four different lighting arrangements was prepared and the differences between the perception of the participants under each lighting arrangement was analysed. The results suggested that different lighting arrangements affect perception. Wall washing enhanced the impressions of clarity and order, cove lighting enhanced spaciousness and order and uplighting made the same space relaxing, private and pleasant.Item Open Access Excitonic improvement of colloidal nanocrystals in salt powder matrix for quality lighting and color enrichment(OSA - The Optical Society, 2016) Erdem, T.; Soran-Erdem, Z.; Kelestemur, Y.; Gaponik, N.; Demir, Hilmi VolkanHere we report excitonic improvement in color-converting colloidal nanocrystal powders enabled by co-integrating nonpolar greenand red-emitting nanocrystal energy transfer pairs into a single LiCl salt matrix. This leads to nonradiative energy transfer (NRET) between the cointegrated nanocrystals in the host matrix. Here we systematically studied the resulting NRET process by varying donor and acceptor concentrations in the powders. We observed that NRET is a strong function of both of the nanocrystal concentrations and that NRET efficiency increases with increasing acceptor concentration. Nevertheless, with increasing donor concentration in the powders, NRET efficiency was found to first increase (up to a maximum level of 53.9%) but then to decrease. As a device demonstrator, we employed these NRET-improved nanocrystal powders as color-converters on blue light-emitting diodes (LEDs), with the resulting hybrid LED exhibiting a luminous efficiency >70 lm/Welect . The proposed excitonic nanocrystal powders potentially hold great promise for quality lighting and color enrichment applications.Item Open Access Excitonics of semiconductor quantum dots and wires for lighting and displays(Wiley-VCH Verlag, 2013) Guzelturk, B.; Martinez, P. L. H.; Zhang, Q.; Xiong, Q.; Sun, H.; Sun, X. W.; Govorov, A. O.; Demir, Hilmi VolkanIn the past two decades, semiconductor quantum dots and wires have developed into new, promising classes of materials for next-generation lighting and display systems due to their superior optical properties. In particular, exciton-exciton interactions through nonradiative energy transfer in hybrid systems of these quantum-confined structures have enabled exciting possibilities in light generation. This review focuses on the excitonics of such quantum dot and wire emitters, particularly transfer of the excitons in the complex media of the quantum dots and wires. Mastering excitonic interactions in low-dimensional systems is essential for the development of better light sources, e.g., high-efficiency, high-quality white-light generation; wide-range color tuning; and high-purity color generation. In addition, introducing plasmon coupling provides the ability to amplify emission in specially designed exciton-plasmon nanostructures and also to exceed the Forster limit in excitonic interactions. In this respect, new routes to control excitonic pathways are reviewed in this paper. The review further discusses research opportunities and challenges in the quantum dot and wire excitonics with a future outlook.Item Open Access Förster resonance energy transfer enhanced color-conversion using colloidal semiconductor quantum dots for solid state lighting(American Institute of Physics, 2009-10-15) Nizamoglu, S.; Demir, Hilmi VolkanIn this paper, we present Förster resonance energy transfer (FRET)-enhanced color-conversion using colloidal semiconductor quantum dot nanocrystals (NCs) to make reddish-orange light-emitting diodes for use in ultraefficient solid state lighting. To achieve FRET enhancement at 614 nm, we use an energy gradient hybrid structure made of cyan- and orange-emitting CdSe/ZnS NCs (λPL =492 and 588 nm in solution, respectively). This enables recycling of trapped excitons using FRET and achieves a relative quantum efficiency enhancement of 15.1% in reddish-orange full color-conversion for the integrated hybrid cyan-orange NC layer with respect to the case of full color-conversion using only orange NCs without FRET.Item Open Access High-stability, high-efficiency organic monoliths made of oligomer nanoparticles wrapped in organic matrix(American Chemical Society, 2016) Soran-Erdem Z.; Erdem, T.; Gungor K.; Pennakalathil, J.; Tuncel, D.; Demir, Hilmi VolkanOligomer nanoparticles (OL NPs) have been considered unsuitable for solid-state lighting due to their low quantum yields and low temperature stability of their emission. Here, we address these problems by forming highly emissive and stable OL NPs solids to make them applicable in lighting. For this purpose, we incorporated OL NPs into sucrose matrix and then prepared their all-organic monoliths. We show that wrapping the OL NPs in sucrose significantly increases their quantum yield up to 44%, while the efficiency of their dispersion and direct solid-film remain only at ∼6%. We further showed ∼3-fold improved temperature stability of OL NP emission within these monoliths. Our experiments revealed that a physical passivation mechanism is responsible from these improvements. As a proof-of-concept demonstration, we successfully employed these high-stability, high-efficiency monoliths as color converters on a blue LED chip. Considering the improved optical features, low cost, and simplicity of the presented methodology, we believe that this study holds great promise for a ubiquitous use of organic OL NPs in lighting and possibly in other photonic applications.Item Open Access Highly luminescent CB[7]-based conjugated polyrotaxanes embedded into crystalline matrices(Wiley-VCH Verlag, 2017) Erdem, T.; Idris, M.; Demir, Hilmi Volkan; Tuncel, D.π-Conjugated polymers suffer from low quantum yields (QYs) due to chain–chain interactions. Furthermore, their emission in solid films is significantly quenched due to aggregation leading further decrease in QY. These are the two main issues of these materials hampering their widespread use in optoelectronic devices. To address these issues, here the backbone of poly(9,9′-bis(6″-(N,N,N-trimethylammonium)hexyl)fluorene-alt-co-thiophenelene) is isolated by threading with cucurbit[7]uril (CB7). Subsequently, the conjugated polyrotaxanes are incorporated into organic crystalline matrices to obtain highly efficient color-converting solids suitable for solid-state lighting. Upon threading the polymer backbone with CB7s, although the QY of the resulting polyrotaxane in solution state increases, the quenching problem in their solid state is not completely tackled. To solve this problem, these conjugated polyrotaxanes are embedded into various crystalline matrices and their remarkably high QYs (>50%) in the solution are successfully maintained in the solid state. To demonstrate the suitability of these aforementioned materials for solid-state lighting, a proof-of-concept light-emitting diode is constructed by employing their powders as color converters.Item Open Access Impact of lighting arrangements and illuminances on different impressions of a room(Elsevier, 2007) Durak, A.; Camgöz Olguntürk, N.; Yener, C.; Güvenç, D.; Gürçinar, Y.This study explores whether different lighting arrangements (general lighting, wall washing and cove lighting) and different illuminances (500 and 320 lux) could affect the perception of the same space. An experimental study was conducted to investigate how the qualitative aspects of space (the impressions of a space) could be enhanced with lighting. Hundred participants were first asked to choose the most suitable lighting arrangement for each impression (clarity, spaciousness, relaxation, privacy, pleasantness and order) under the 500 lux illuminance. In the second stage, they were asked to compare the two illuminances (500 and 320 lux) for the lighting arrangement they selected in the first stage. There was a statistically significant relation between impressions and lighting arrangements, also between impressions and lighting levels. Thus, different lighting arrangements and lighting levels could be used to enhance the clarity, spaciousness, relaxation, privacy, pleasantness and order of a room. The results of this study found most suitable lighting arrangements with their illuminances for each impression, which is reported in the paper. © 2006 Elsevier Ltd. All rights reserved.Item Open Access Implementation of high-quality warm-white light-emitting diodes by a model-experimental feedback approach using quantum dot-salt mixed crystals(American Chemical Society, 2015) Adam, M.; Erdem, T.; Stachowski, G.M.; Soran-Erdem Z.; Lox, J. F. L.; Bauer, C.; Poppe, J.; Demir, Hilmi Volkan; Gaponik N.; Eychmüller A.In this work, a model-experimental feedback approach is developed and applied to fabricate high-quality, warm-white light-emitting diodes based on quantum dots (QDs) as color-conversion materials. Owing to their unique chemical and physical properties, QDs offer huge potential for lighting applications. Nevertheless, both emission stability and processability of the QDs are limited upon usage from solution. Incorporating them into a solid ionic matrix overcomes both of these drawbacks, while preserving the initial optical properties. Here borax (Na2B4O7·10H2O) is used as a host matrix because of its lower solubility and thereby reduced ionic strength in water in comparison with NaCl. This guarantees the stability of high-quality CdSe/ZnS QDs in the aqueous phase during crystallization and results in a 3.4 times higher loading amount of QDs within the borax crystals compared to NaCl. All steps from the synthesis via mixed crystal preparation to the warm-white LED preparation are verified by applying the model-experimental feedback, in which experimental data and numerical results provide feedback to each other recursively. These measures are taken to ensure a high luminous efficacy of optical radiation (LER) and a high color rendering index (CRI) of the final device as well as a correlated color temperature (CCT) comparable to an incandescent bulb. By doing so, a warm-white LED with a LER of 341 lm/Wopt, a CCT of 2720 K and a CRI of 91.1 is produced. Finally, we show that the emission stability of the QDs within the borax crystals on LEDs driven at high currents is significantly improved. These findings indicate that the proposed warm-white light-emitting diodes based on QDs-in-borax hold great promise for quality lighting. © 2015 American Chemical Society.Item Open Access Improved InGaN/GaN light-emitting diodes with a p-GaN/n-GaN/p-GaN/n-GaN/p-GaN current-spreading layer(Optical Society of American (OSA), 2013) Zhang, Z.-H.; Tan, S.T.; Liu W.; Ju, Z.; Zheng, K.; Kyaw, Z.; Ji, Y.; Hasanov, N.; Sun X.W.; Demir, Hilmi VolkanThis work reports both experimental and theoretical studies on the InGaN/GaN light-emitting diodes (LEDs) with optical output power and external quantum efficiency (EQE) levels substantially enhanced by incorporating p-GaN/n-GaN/p-GaN/n-GaN/p-GaN (PNPNP-GaN) current spreading layers in p-GaN. Each thin n-GaN layer sandwiched in the PNPNP-GaN structure is completely depleted due to the built-in electric field in the PNPNP-GaN junctions, and the ionized donors in these n-GaN layers serve as the hole spreaders. As a result, the electrical performance of the proposed device is improved and the optical output power and EQE are enhanced. © 2013 Optical Society of America.Item Open Access The influence of sustainable design features on indoor environmental quality satisfaction in Turkish dwellings(Taylor & Francis, 2016) Afacan, Yasemin; Demirkan, H.The aim of this paper is to explore the influence of sustainable design features on occupants satisfaction levels with indoor environmental quality (IEQ) aspects in three types of dwellings. Satisfaction level was investigated through a field survey with 240 participants, in apartments, row and detached houses in Turkey. Satisfaction level was explored in terms of overall satisfaction with IEQ, with the efficiency of daily living activities and with sleeping quality. Satisfaction level was also investigated regarding the dwellings thermal, ventilation, lighting, sound level and moisture qualities. The findings indicate that the existence of exterior insulation, a thermostat, light dimmers and control of daylighting systems through operable windows have high impacts on the satisfaction level of occupants living in all three types of dwellings. © 2015 Informa UK Limited, trading as Taylor & Francis Group.