Task -Ambient lighting provides energy saving but space surrounding the users can be dim and unpleasant. This study proposed a solution of an additional Surround Layer of light. Though a series of simulated lighting scenarios, it examined illumination requirements, dimensionality and appearance of the space by the use of Vector/Scalar and Task/Vertical Illumination Ratios. They were evaluated under several illuminance requirements, Task-Surround combinations and Surround Light source sizes. The results showed that by adding a Surround Light Layer, visual appearance of space surrounding the users could be enhanced and energy savings could be achieved.
A new method by using a pulsed-laser Raman scattering technique was employed to estimate junction temperature of a fluorescence-resin-less blue-LED package. Temperature dependent Raman shift of E 2 H mode of GaN layer in the blue-LED were obtained and were in good agreement with the experimental data published by the other researchers. This technique was applied to estimation of a junction temperature of the light-emitting blue-LED. The junction temperature was successfully estimated even under the strong stray light and LED light emission. It is considered that the proposed technique would be a remote and standard system for measuring the junction temperature of light-emitting white-LEDs.
By modulating the indium composition in the quantum barriers of InGaN-based LEDs, the influence of electron distribution, electron overflow and Auger recombination on the external quantum efficiency (EQE) and droop effect have been investigated. Experimental results as well as numerical simulations reveal that the electron distribution is the key factor to influence both the peak efficiency and droop effect. The results show that the high electron concentration in the individual quantum well can stimulate the Auger recombination and lead to the droop effect instead of the total effective electron concentration, which is more related to the external quantum efficiency. If we modulate the indium composition in the quantum barriers of the InGaN-based LEDs, a uniform electron distribution can be achieved, which can not only enhance the EQE but also avoid the Auger recombination and improve the droop effect.
Results of the project ‘ODALINE’ (OLED Devices Application in Luminaires for Interior and Exterior lighting) are presented. A team of academic and industrial partners worked together to design and manufacture a family of OLED luminaires. The project went through the following phases: i) analysis of the state-of-the-art of OLED technology; ii) identification of scenarios and application fields for OLED-based lighting systems and definition of requirements and performances expected for each scenario; iii) definition of the concept of new OLED lighting systems and development of their preliminary design; iv) executive design and manufacturing of some prototypes. After the identification of the most suitable OLED unit and of the application scenarios, the concept of the new luminaires was conceived: the luminaires rely on a suitable aggregation of a base module (consisting of an array of 6 OLED units, measuring 30 cm ∗ 20 cm) to provide systems with enhanced properties in terms of high efficiency, high quality light and flexibility as the luminaires can be combined to respond to different lighting tasks for indoor environmental applications. Final output of the research project was the manufacturing of three prototypes: a suspended luminaire (6 basic modules), a free-standing luminaire (4 basic modules) and a task lighting luminaire (1 module). The power supply system, consistently with the general concept, was developed for a single module rather than for the whole luminaire. Its architecture was conceived to allow the control of the luminaire (switching on/off, dimming) through the DALI digital protocol. Furthermore, some secondary optics were conceived and designed to concentrate the Lambertian light output and to increase the utilization factor of the flux.
The synthesis of visible light communication (VLC) and lighting state control necessitates data-light modulation that can accommodate intensity control. A number of techniques that enable both optical wireless data transmission and intensity control of light-emitting diodes (LEDs) have been proposed as a response to this need. Relevant schemes leverage amplitude modulation (AM)/continuous current reduction (CCR) and/or pulse-width modulation (PWM) for dimming capability. Two-level schemes related to PWM, such as on-off keying with compensation time (OOK + CT), variable pulse position modulation (VPPM), and multiple pulse position modulation (MPPM), are most commonly investigated. In this paper, we survey and compare OOK + CT, VPPM and MPPM. Moreover, we propose a novel approach towards dimming and data transmission through the variation of codeword weights in overlapping pulse-position modulation (OPPM). The proposed approach has comparatively high spectral efficiency. Using realistic constraints of a practical VLC system, analysis reveals that OPPM can increase data rates by more than 20Mbps over expected performance of related, two-level schemes, when using LEDs suitable for lighting that have relatively low modulation bandwidths.
ZrO 2 light diffuser layers was placed on phosphor-in-glass composites (PiGs) to improve color uniformity of white-light-emitting diodes (white LEDs). Color coordinates of central part and periphery of white LEDs were (0.34, 0.38) and (0.36, 0.43), respectively; difference between two area decreases with the introduction of a diffuser layer. Color temperature difference also decreased from 770 to 464 K. The addition of diffuser layers reduced the luminous efficacy of the white LEDs from 90.3 to 83.4 lm/W.
LED luminaires are already beyond retrofit systems, which are limited in heat dissipation due to the old fitting standards. Actual LED luminaries are based on new LED packages and modules. Heat dissipation through the first and second level interconnect is a key issue for a successful LED package. Therefore the impact of known bonding technologies as gluing and soldering and new technologies like sintering and transient liquid phase soldering were analyzed and compared. A realized hermetic high power LED package will be shown as example. The used new techniques result in a module extremely stable against further assembly processes and harsh operating conditions.
White organic light emitting diodes (WOLEDs) have gained considerable attention of academic and industrial research communities as promising alternative to incandescent lamps, fluorescent tubes and inorganic LEDs for low energy consumption lighting applications. WOLEDs are expected to become one of the next generation lighting sources because of their high color tunability and color quality, which can be easily achieved by proper chemical design of organic electroluminescent materials. Contrary to their inorganic counterparts, WOLEDs also bear the distinctive feature of being available as flexible and large area devices. Over the last decades, a lot of efforts have been spent on defining suitable strategies to highly efficient WOLEDs based on the use of properly tailored organic emitters. Here we survey the main chemical approaches to white electroluminescence from organic light emitting materials, highlighting strong and weak points of each strategy. Current research on new hybrid white light emitting devices based on the combination of inorganic LEDs and organic down color converters is also reviewed by some representative examples.
We report on the methodology and implementation of a robust and accurate double integrating sphere system for measuring the absolute photoluminescence quantum yield and its temperature dependence of commercially available phosphors (garnets, silicates and nitrides). The potential of our instrument for the examination of light interaction with samples of different absorption and diffusion coefficients is also presented, as optical properties of luminescent materials have a major impact on the efficiency of LED’s packaging. Our work gives special attention to the control and the optimization of light losses in the optical system in order to ensure reliable measurements. The YAG:Ce phosphor shows the highest luminescence quantum yield at 97% efficiency, the green silicate the lowest with 79% efficiency. Silicate phosphors show up to 15% loss of luminescence intensity when temperature is raised to 140°C.
The SSL Annex was established in 2010 under the framework of the International Energy Agency’s Energy Efficient End-use Equipment (4E) Implementing Agreement to provide advice to its ten member countries seeking to implement quality assurance programs for SSL lighting. This international collaboration brought together the governments of Australia, China, Denmark, France, Japan, The Netherlands, Republic of Korea, Sweden, United Kingdom and United States of America. China worked as an expert member of the 4E SSL Annex. The SSL Annex completed its first term in June 2014 and started on its second five-year term in July 2014. During the first term, the Annex had undertaken three major collaborative tasks on (1) Quality Assurance, (2) SSL Testing and (3) Standards & Accreditation. On quality assurance, the Annex worked to develop a set of performance tiers aimed to identify a suite of metrics and values related to minimum performance values of SSL for energy efficiency, lighting quality, and safety. Reports on SSL products and LCA aspects as well as SSL products and health aspects were developed within this task. For SSL Testing, the Annex has sought to promote harmonisation of SSL quality and performance testing around the world by establishing the world’s largest interlaboratory comparison (IC 2013) of SSL laboratories with more than 110 laboratories compared around the world. And for Standards and Accreditation, the Annex worked to establish suitable accreditation frameworks for laboratories participating in IC 2013, promoting worldwide mutual recognition of PT. The Annex started its second term in July 2014, and will run through June 2019. The new work plan continues some of the activities undertaken in the first term, but also tackles new challenges such as lifetime testing and market monitoring, verification and enforcement.
We reviewed the role of melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) in light-dependent functions, including circadian rhythm that is important for health and visual perception. We then discussed the implications for lighting design.
A thin optical reflector is often introduced to the backside of the standard mesa type light emitting diode (LED) chip with the aim to enhance its light output. However, most of the reported light output enhancements because of backside reflector (BR) introduction might not be relevant. This is because the reported measurement is often from a naked LED chip instead of a packaged LED emitter, and those based on the packaged emitters employing conventional silver based die attach adhesive (DAA). The actual role of BR, which is expected to be greatly influenced by the packaging materials and processes, is investigated for the monotonic blue color and white LED emitters using Monte-Carlo simulations. Contrary to prior reports, it is demonstrated for the first time that the role of BR can be diminished when the optically transparent DAA is used and other key packaging materials and processes are optimized, i.e., the light output for a packaged emitter with a BR-free chip can be as high as that of the packaged emitter using the same chip but with an added BR.
Through a series of experiments, we have measured the extent to which 3D visualizations of a variety of lighting conditions in an indoor environment can accurately convey primary perceptual attributes. Our goal was to build and rigorously test perceptually accurate visual simulation tooling, which can be valuable in the design, development, and control of complex digital solid-state lighting systems. The experiments included assessments of lighting-related perceptual attributes in a real-world environment and a variety of virtual presentations. Iteratively improving choices in modeling, light simulation, tonemapping, and display led to a robust and honest visualization pipeline that provides a perceptual match of the real world for most perceptual attributes and that is nearly equivalent in perceptual performance to photography. One persistently difficult attribute is scene brightness, as observers consistently overestimate the brightness of dimmed scenes in virtual presentations. In this paper we explain the experimental 3D visualization pipeline variables that were addressed, the perceptual attributes that were measured, and the statistical methods that were applied to evaluate our success.
With the excellent thermal conductivity and the compatibility to micro electromechanical systems technology, silicon is widely used in micro heat pipes (MHPs). Copper shows higher heat transfer capability and capillary traction than silicon. Copper microgrooves were fabricated on the silicon wafer using electroforming technique in this paper. Water contact angle measurements and thermal behavior tests demonstrated that copper-grooved MHPs showed better performance than silicon ones. Under the input power of 5.99 W, the equivalent thermal conductivities of copper-grooved and silicon-grooved MHPs were 228.98 W/K · m and 196.26 W/K · m. This work showed the feasibility of copper grooved silicon based MHPs in heat transfer for high-power light emitting diode (HP LED).
A low-cost and high performance Ag-coated Cu flakes filled epoxy was prepared as electrically conductive adhesives (ECAs) for light emitting diode (LED) packaging. As-prepared ECAs consisted of bisphenol-F-epoxy resin, micro-sized Ag-coated Cu flakes and other additives. The ECAs with content of 70 wt % Ag-coated Cu flakes pre-modified by silane coupling agent (SCA) exhibited much lower bulk resistivity (8.4*10 −3 Ωcm) than that of ECA filled with 70 wt % Ag-coated Cu flakes without SCA modification (1.6*10 −1 Ωcm). An appropriate content of diluent (below 20 wt %) was beneficial for the flakes’ regular dispersion in resin, which enhanced the electrical conductivity (10 −4 ~ −10 −5 Ωcm) and mechanical strength (>14 Mpa) of ECAs.
Energy has been identified as one of the most important problems during the last few years. One of energy efficient technologies may reduce consumed energy in buildings from 20 percent to less than 5 percent. A novel lighting technology has recently been evolved as light emitting diodes (LEDs) that can be over 7–10 times more efficient than conventional-old incandescent lamps. Therefore, LED lighting systems have been rapidly replacing conventional energy-hungry lighting products like incandescent lamps and more recently environmentally hazardous fluorescent lamps. While LEDs may produce large amounts of lumens, they are solid state based technologies similar to computer chips so they have to be kept cool at certain chip junction temperature. The demand for high light output LED systems lead to significant heat generation rates, so that higher heat fluxes result in elevated junction temperatures on LED chips in SSL lighting systems. Moreover, the changes on the junction temperature strongly impact the reliability, lifetime, light output and quality of the light. Because of their simplicity, reliability, low cost and silent operation, passive air-cooling systems are preferred in LED lamps. Passive metal based heat sinks are the main cooling components of typical LED lamps serves for both LEDs and driver electronics. Heat is dissipated generally from finned surfaces to ambient air with primarily convection mechanism and partially radiation. But it requires a large surface area and weight under the limitations of the standardized lamps. Thus, the optimization of the heat sink in an LED system is crucial. Developing figure of merits (FOM) is very important for designers and researchers to find the most optimal solution accounting for critical metrics such as size, weight, cost and performance. In the present study, thermal, electrical and optical experimental results of various commercial A-line LED lamps are investigated and a number of FOMs are proposed based on the performance, size and weight. Proposed FOMs aim to evaluate different aspects by combining a number of performance metrics. Results show that one can combine and analyze multi-purpose design parameters for thermal, electrical and optical performances and manufacturing for engineers and consumers.
The luminescence properties of the blue emitting phosphor Sr 0.25 Ba 0.75 Si 2 O 2 N 2 :Eu 2+ are extensively investigated. This oxonitridosilicate phosphor features strong 4f 6 5d 1 - 4f 7 luminescence originating from the Eu 2+ ion, with a narrow emission band peaking at 467 nm and a full width at half maximum of only 41 nm. Thermal quenching of the blue luminescence only sets in above 450 K, making this material an interesting candidate as LED conversion phosphor. The fast decay of the luminescence prevents the phosphor to be susceptible to saturation effects at high excitation fluxes. Furthermore it is proven to be chemically stable against moisture. The only drawback is the relatively low quantum efficiency of the synthesized powder, provisionally preventing this material to be used in applications. In addition, the phosphor features a weak yellow emission band, originating from small domains featuring a different crystal structure. It is shown that the majority of the powder grains only exhibit blue emission. Finally, the spectrum of a white LED, based on a UV pumping LED and three (oxy)nitride phosphors is simulated in order to assess the usefulness of blue phosphors in LEDs for lighting. Only a marginal improvement in terms of color quality can be achieved with a narrow banded phosphor, at the expense of a decrease in luminous efficacy and overall electrical to optical power efficiency. PACS 70 – Condensed Matter: Electronic structure, Electrical, Magnetic, and Optical Properties PACS 42.70.-a Optical materials
The advent of modern light-emitting diode (LED) techniques enables us to develop novel lighting systems with numerous previously unavailable features. Specifically, by using the fixtures for both illumination and to interrogate the space, source-to-sensor communication becomes possible at very low cost. In this paper, we present a novel framework to estimate the occupancy distribution in an indoor space using color-controllable LED fixtures (the same fixtures providing the illumination, simultaneously) and sparsely distributed non-imaging color sensors. By modulating randomly generated perturbation patterns onto the drive signals of the LED fixtures and measuring the changes in the color sensor responses, we are able to recover a light transport model for the room. Two approaches are proposed to estimate the spatial distribution of the occupancy, based on a light blockage model and a light reflection model, respectively. These two approaches, which can be combined, can faithfully reveal the occupancy scenario of the indoor space, while preserving the privacy of its occupants. An occupancy-sensitive lighting system can be designed based on this technique.
In this work, we studied the thermal behavior and addressed the challenges of life testing of large area OLED devices. In particular, we developed an indirect method to accurately calculate the life time of large-area OLED lighting panels without physically life-testing the panels. Using small area OLEDs with structures identical with the tested panels, we performed the life tests at desired driving current densities at different temperatures and extracted the relationship between junction temperature and the lifetime for the particular device. By measuring the panel junction temperature during operation under the same current density and using the life time measured on small area test devices, we determine the lifetime of the panels based on the thermal dependence. We test this methodology by predicting the life time of white PHOLED panels and then physically testing the panels. The typical result for the lifetime to 80% of the initial luminance (LT80) of the panel at a constant dc current density of 10 mA/cm 2 (3800 cd/m 2 ), was predicted to be 526 hours in good agreement with the actual life-test at 10 mA/cm 2 of 512 hrs. This good agreement, confirmed in different experiments, validates this novel technique as a practical life time predictor of large-area OLED lighting panels in a time saving manner.
For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the individual sources of error for correlated colour temperature (CCT) reproducibility and maintenance under control. In this regard, it is of essential importance to understand how geometrical, optical and thermal properties of the colour conversion elements (CCEs), which typically consist of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired CCT value. In this contribution we use an LED assembly consisting of an LED die mounted on a printed circuit board by chip-on-board technology and a CCE with a globe-top configuration on the top of it as a model system and discuss the impact of the CCE size, the substrate reflectivity as well as the thermal load of the CCEs on CCT maintenance and the respective radiant fluxes. It turns out that optimized solutions for CCT maintenance and high radiant fluxes in regard of one of the relevant influence factors do not need to be optimized solutions in regard of another one.
