Nonmonotonic Phosphor Size Dependence of Luminous Efficacy for Typical White LED Emitters (original) (raw)
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Studies of Phosphor Concentration and Thickness for Phosphor-Based White Light-Emitting-Diodes
Journal of Lightwave Technology, 2008
The dependence of luminous efficacy on phosphor concentration and thickness for high-power white light-emitting-diode (WLED) lamps is investigated by employing three-dimensional ray-tracing simulations. The simulations show that the brightness or luminous efficacy of WLED lamps highly depends on the combination of phosphor concentration and phosphor thickness (or phosphor-matrix composite volume). The package with lower concentration and higher phosphor thickness has higher luminous efficacy because the light trapping efficiency is lower with the low phosphor concentration. At the correlated color temperature (CCT) value of around 4000 K, ray-tracing simulation and experimental results show 20% and 23% improvement in lumen, respectively, with a 1.8-mm-phosphor package over a 0.8-mm-phosphor package. A package with convex lens can improve the lumen output over flat lens, but this improvement is small, and it requires higher amount of phosphor, up to 25%, to achieve same CCT value.
IEEE Journal of Selected Topics in Quantum Electronics, 2009
Based on optical ray tracing, we discuss the effect of the phosphor particle sizes on the angular homogeneity of the light emitted from phosphor-converted LEDs. Since the blue LED and the yellow-converted light have rather different emission characteristics, which have to be harmonized to one another by the scattering processes within the color conversion element, the phosphor particle size turns out to be an essential parameter in order to attain angular homogeneity. This can be attributed, on the one hand, to the number of scattering processes within a specific unit volume for a given phosphor concentration, and on the other hand, to the specific scattering functions, both of which depend on the phosphor particle diameter.
IEEE Photonics Technology Letters, 2011
In this work, we studied the effect of different packaging parameters on the angular homogeneity of correlated color temperature (CCT) in phosphor-in-cup light-emitting diode (LED) packages, including phosphor particle concentration, phosphorlayer surface curvature, and lens surface curvature, using a Monte Carlo ray tracing simulation tool. An optimized packaging geometry with convex phosphor layer was achieved with good CCT uniformity and highest lumen efficiency. Moreover, an approach was developed for the prediction of color uniformity and lumen efficiency when varying the surface curvature of either phosphor layer or clear lens, since the inconsistency of phosphor layer or lens cap happened commonly to the fabricated phosphor conversion white LEDs (pc-WLEDs).
Electrical–thermal–luminous–chromatic model of phosphor-converted white light-emitting diodes
Applied Thermal Engineering, 2014
The drive of increased electrical currents to achieve high luminous output for Phosphor-converted White Light-Emitting Diodes (PW-LED) has led to a series of thermal problems. The light performance of PW-LED is affected by the heat generated by the two major sources in a package/module: chip(s) and phosphors. In this work, spectral shift and consequent color properties change due to the increased temperature during operation were studied by a group of experiments. An electrical-thermal-luminous-chromatic (E-T-L-C) model was then developed to predict the light performance with thermal management under in-situ temperature. The model was then validated by integrated analyses of common LED packages. Besides, the model can also be used to analyze the thermal performance and light quality due to thickness and particle density variation of phosphors. The proposed dynamic E-T-L-C model can definitely benefit the design of future HB LEDs for better light quality.
TELKOMNIKA Telecommunication Computing Electronics and Control, 2020
The remote phosphor structure is disadvantageous in color quality but more convenient in luminous flux when compared to conformal phosphor or in-cup phosphor structure. From this disadvantage, there are many studies to improve the color quality of the remote phosphor structure. This research will propose a dual-layer remote phosphor structure to improve color rendering index (CRI) and color quality scale (CQS) of WLEDs. The WLED package with color temperature of 8500 K is utilized in this study. The idea of the study is to locate a layer of phosphor green Y2O2S:Tb3+ or red ZnS:Sn2+ on the yellow phosphor YAG:Ce3+ film, and then finding the suitable added concentration of ZnS:Sn2+ to match the highest color quality. The results showed that ZnS:Sn2+ brings great benefits to increase CRI and CQS. The greater the ZnS:Sn2+ concentration is, the higher the CRI and CQS become owing to the rise in red light components in WLEDs. Meanwhile, the green Y2O2S:Tb3+ phosphor brings benefits to luminous flux. However, the decrease in luminous flux and color quality occurs when the concentration of ZnS:Sn2+ and Y2O2S:Tb3+ exceeds the corresponding level. This is proved by applying Mie-scattering theory and Lambert-Beer's law. The results of articles are important for WLEDs’ fabrication having higher white light quality.
A novel phosphor structure for improving the luminous flux of white LEDs
Bulletin of Electrical Engineering and Informatics, 2022
This section focuses on the color uniformity and luminous production of multi-chip white-emitted LED lighting systems (MCW-LEDs) in improving illuminated performance. To accomplish the desired outcome, CaO:Sb 3+ must be mixed with their phosphor compounding, which has been shown to have a massive impact on illuminating effectiveness. There is also evidence that the increasing of yellowish-green-emitted phosphorus CaO:Sb 3+ concentration supports color homogeneity as well as luminescent effectiveness enhancements in MCW-LEDs featuring a 8500 K correlating colour temperature (CCT). Meanwhile, that rise in CaO:Sb 3+ concentration leads to the gradually deteriorating color quality scale. Thus, if appropriate concentration and particle size of CaO:Sb 3+ phosphor are determined, it is not hard to obtain such an excellent presentation in color uniformity, color quality scale and luminescence of MCW-LEDs.
Luminous efficiency enhancement of white light-emitting diodes by using a hybrid phosphor structure
Journal of Photonics for Energy, 2015
This paper presents a "hybrid" structure for the coating of yellow YAG∶Ce3 þ phosphor on blue GaN-based light-emitting diodes (LEDs). The luminous efficiency of the hybrid phosphor structure improved by 5.9% and 11.7%, compared with the conventional remote and conformal phosphor structures, respectively, because of the increased intensity of the yellow component. The hybrid structure also has an advantage in the phosphor usage reduction for the LEDs. Furthermore, the electric intensity of the hybrid phosphor structure was calculated for various thicknesses by conducting TFCalc32 simulation, and the enhanced utilization of blue rays was verified. Finally, the experimental results were consistent with the simulation results performed using the Monte-Carlo method.
Effect of Chip Wavelength and Particle Size on the Performance of Two Phosphor Coated W-LEDs
Transactions on Electrical and Electronic Materials, 2014
Most commercial white LED lamps use blue chip coated with yellow emitting phosphor. The use of blue excitable red and green phosphors is expected to improve the CRI. Several phosphors, such as SrGa 2 S 4 :Eu 2+ and (Sr,Ba)SiO 4 :Eu 2+ , have been suggested in the past as green components. However, there are issues of the sensitivity and stability of such phosphors. Here, we describe gallium substituted YAG:Ce 3+ phosphor, as a green emitter. YAG structures are already accepted by the industry, for their stability and efficiency. LEDs with improved CRI could be fabricated by choosing Y 3 Al 4 GaO 12 :Ce 3+ (green and yellow), and SrS:Eu 2+ (red) phosphors, along with blue chip. Also, the effect of a slight change in chip wavelength is studied, for two phosphor-coated w-LEDs. The reduction in particle size of the coated phosphors also gives improved w-LED characteristics.
Essential Factor for Determining Optical Output of Phosphor-Converted LEDs
IEEE Photonics Journal, 2014
An essential factor of the particle number is exploited for the phosphor excitation in phosphor-converted white LEDs. The particle number can clearly reveal the dependence of the light output flux and the correlated color temperature upon the conventional parameters, thickness, and concentration of the phosphors in a simpler way. In addition, we also find that there might exist an optimal particle number for the maximal luminous light output. An empirical function is then proposed for successfully modeling the relation between the output light and the particle number.
XI Brazilian Power Electronics Conference, 2011
This paper describes an experimental photometrical analysis regarding two mainstreams inside the high-brightness LED family: the power devices, socalled high power LEDs, and the low power devices. Focus is given to white phosphor-converted LEDs, which are used in LED-based luminaires for indoor and outdoor lighting. Data from several LEDs used in available luminaires are compiled and provided as photometrical references for the design considerations in light output of LED drivers which employ power electronic converters.