Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

Heat and fluid flow in high-power LED packaging and applications

Light emitting diodes, LEDs, historically have been used for indicators and produced low amounts of heat. The introduction of high brightness LEDs with white light and monochromatic colors have led to a movement towards general illumination. The increased electrical currents used to drive the LEDs have focused more attention on the thermal paths in the developments of LED power packaging. The luminous efficiency of LEDs is soon expected to reach over 80 lumens/W, this is approximately 6 times the efficiency of a conventional incandescent tungsten bulb. Thermal management for the solid-state lighting applications is a key design parameter for both package and system level. Package and system level thermal management is discussed in separate sections. Effect of chip packages on junction to board thermal resistance was compared for both SiC and Sapphire chips. The higher thermal conductivity of the SiC chip provided about 2 times better thermal performance than the latter, while the under-filled Sapphire chip package can only catch the SiC chip performance. Later, system level thermal management was studied based on established numerical models for a conceptual solid-state lighting system. A conceptual LED illumination system was chosen and CFD models were created to determine the availability and limitations of passive air-cooling.

Thermal management of LEDs: Package to system

Increasing the reliability of solid state lighting systems via self-healing approaches: A review

Recently, high-power white light-emitting diodes (LEDs) have attracted much attention due to their versatility in applications and to the increasing market demand for them. So great attention has been focused on producing highly reliable LED lighting. How to accurately predict the reliability of LED lighting is emerging as one of the key issues in this field. Physics-of-failure-based prognostics and health management (PoF-based PHM) is an approach that utilizes knowledge of a product's life cycle loading and failure mechanisms to design for and assess reliability. In this paper, after analyzing the materials and geometries for high-power white LED lighting at all levels, i.e., chips, packages and systems, failure modes, mechanisms and effects analysis (FMMEA) was used in the PoF-based PHM approach to identify and rank the potential failures emerging from the design process. The second step in this paper was to establish the appropriate PoF-based damage models for identified failure mechanisms that carry a high risk.

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Physics-of-Failure-Based Prognostics and Health Management for High-Power White Light-Emitting Diode Lighting

The lifetime of an actively-cooled light emitting diode (LED)-based luminaire is dependent not only on the junction temperature of LEDs, but also on the reliability of active cooling devices. We propose a novel hierarchical model to assess the lifetime of an actively cooled LED-based luminaire that can provide light output equivalent to a 100 W incandescent lamp. After design considerations for LED-based luminaires with active cooling are discussed, the proposed model is described using component-level sub-physics-of-failure models. The model is implemented to predict the lifetime of a LED-based recessed downlight with synthetic jet cooling. The effects of the time-dependent performance degradation mechanisms of the active cooling device on the lifetime of the luminaire are also discussed.

Hierarchical Life Prediction Model for Actively Cooled LED-Based Luminaire

Lumen depreciation and color quality change of phosphor-converted LED (pc-LED) are caused by the combination of various degradation mechanisms including chip, phosphor layer, and packaging material degradations. We present an analytical/experimental hybrid procedure to quantify the effect of each mechanism on pc-LED degradation. A mathematical model based on the spectral power distribution (SPD) is proposed after defining each degradation parameter. The model decomposes effectively the SPD change caused by the degradation into the contributions of individual degradation mechanisms. The model is implemented using the SPDs of a pc-LED with conformally coated phosphor, obtained before and after 9000 hours of operation. The analysis quantifies the effect of each degradation mechanism on the final values of lumen, CCT, and CRI.

Analytical/Experimental Hybrid Approach Based on Spectral Power Distribution for Quantitative Degradation Analysis of Phosphor Converted LED

We propose a procedure to deconvolute the spectral power distribution (SPD) of phosphor-converted LEDs (pc-LEDs). The procedure involves a two-step process using multiple Gaussian functions. The first step is a preliminary process to deconvolute an SPD using a pair of Gaussian functions. Using the results from the first step, the second step determines (a) the number of Gaussian functions to be used in the analysis and (b) the initial values and regression domains of the coefficients of each Gaussian function for subsequent multiple-regression operations. Successful deconvolution is confirmed by comparing the values of lumen, correlated color temperature, and color rendering index with the experimental data of cool and warm pc-LEDs. The proposed approach is illustrated to evaluate the yellow-to-blue ratio and the phosphor power conversion efficiency.

Spectral power distribution deconvolution scheme for phosphor-converted white light-emitting diode using multiple Gaussian functions

https://www.prognostics.umd.edu/calcepapers/Optimum_design_domain_of_LED-based_solid_state_lighting.pdf

Optimum design domain of LED-based solid state lighting considering cost, energy consumption and reliability

Coupled thermal and mechanical design issues in a high power light emitting diode (LED) package platform are investigated using numerical models. A thermal resistance network model and a 3-D finite element model are built for thermal and stress analyses. They are validated with the experimental data and subsequently utilized to study the effect of key parameters on the junction temperature and the thermal strains. An extensive parametric analysis is conducted to assess the effect of design and material parameters on the junction temperature and thermal strains of the high power LED under study. Based on the results, the desired parameters of adhesives for high power LED applications are identified and an example of an LED thermo-mechanical design protocol is presented.

Bong-Min Song

Papers

Hierarchical Life Prediction Model for Actively Cooled LED-Based Luminaire

Analytical/Experimental Hybrid Approach Based on Spectral Power Distribution for Quantitative Degradation Analysis of Phosphor Converted LED

Spectral power distribution deconvolution scheme for phosphor-converted white light-emitting diode using multiple Gaussian functions

Optimum design domain of LED-based solid state lighting considering cost, energy consumption and reliability

Coupled Thermal and Thermo-Mechanical Design Assessment of High Power Light Emitting Diode