Production Of Light-emitting Diodes Research Articles

Life cycle assessment of high-power white LEDs for indoor lighting in the context of Hong Kong

The introduction of white light-emitting diodes (LEDs) is one of the key innovations that has revolutionized the lighting industry due to its multiple benefits. Despite their advantages, there is a gap in the environmental impact information of the recently developed high-power LED products within the whole lifecycle, which is a key step to achieve sustainable and green development. This life cycle assessment (LCA) is conducted by considering the cradle-to-grave system boundary. The functional units considered are a LED and compact fluorescent lamp (CFL) of 40 million lumen-hours (lm-h) used for indoor applications over an operating time of 20 000 h. In this study, the LCA was carried out using the SimaPro software and built-in ecoinvent database V2.2 with appropriate life cycle inventory data. The analysis results indicate that: (1) the LED-package has a dominant environmental impact followed by the LED driver while the housing and corrugated-board packaging materials showed the least negative effect to the ecosystem during the manufacturing phase. On the contrary, the CFL drivers are dominant followed by the light sources in the case of CFLs. From the lifecycle stages, the usage-phase showed a predominant environmental effect, mainly due to the energy consumption and sources of energy production. (2) A scenario analysis on the sources of electricity production revealed that prospective sources (70% natural gas, 25% nuclear and 5% pumped storage) of energy production lowered the environmental impact compared to the current electricity mix. These proposed electricity generation production sources provide a 61% reduction in the global warming potential in light sources for Hong Kong.

Life cycle cost analysis of LED retrofit and luminaire replacements for four-foot T8 troffers

Lighting makes up 17% of electrical loads and the largest energy end use in commercial buildings. Linear fixtures are among the largest opportunities for energy efficiency improvement, given their long operating hours. With continued, rapid light-emitting diode (LED) development and more LED replacement products on the market, lighting replacement decisions become more complex and warrant re-examination. With a goal to inform building managers and other decision-makers with practical guidance on lighting replacement, this study is a life cycle cost (LCC) analysis that compares the cost–benefit of six replacement options (one fluorescent and five LED) for a 0.61 m by 1.22 m (2 ft by 4 ft) T8 recessed troffer based on data for 168 lighting products from an online vendor. Results show that direct wire (i.e. unballasted) LED retrofits are the least-cost option to replacing fluorescent lamps in terms of normalized LCC. Plug-and-play lamps suffer from a lock-in with ballasts, but their ease of installation can help spur LED adoption. In cases where an existing ballast is still usable, hybrid LED retrofits provide the least upfront cost option by deferring the cost of rewiring. LED luminaires can offer improved aesthetics and reliability; however, they have high upfront cost. Among them, luminaires with replaceable lamps offer lower cost than those without.

Effects of (Ba,Ca)ScO2F:Bi3+,K+ phosphor particle size on color uniformity white light-emitting diodes

Phosphors that offer considerable performance as well as heat consistency has been a high priority of recent studies concerning light-emitting diodes (LED) devices. This study employs the perovskite phosphors BCSOF (short for Ba<sub>1-x</sub>Ca<sub>x</sub>ScO<sub>2</sub>F:0.001Bi3+,0.001K+ with x value from 0 to 0.12 and one chip at 415 nm generating thin green illumination via cation-replacement method. The study examines the aftermath when Ca<sup>2+</sup> replaces Ba<sup>2+</sup> within the crystal formations of BCSOF as well as the luminescent features of the phosphors, detecting a formation of cube-like perovskite within the space group of Pm3m in the employed phosphors. In addition, the study also assesses the development concerning the magnitude of cells as well as the binding extent of Ba/Ca/K/Bi-O. When the inner quantum performance reaches 77.4% in BCSOF, a potent green discharge is manifested, reaching 510 nm when excited by a chip at 415 nm. Greater luminescent performance as well as heat consistency correlating with changes in inner formation were reported. Via the method of replacing cations, it is possible to control spectrum by manipulating the latticework’s surroundings, leading to desirable performance in LED products.

Synthesis and optical properties of far-red dual perovskite Sr2InTaO6: Mn4+ phosphors for indoor plant lighting LED

Far-red light at 650–750 nm has a significant effect on plant development. It is of great significance to develop a kind of phosphor that can emit bright far-red light. In this paper, we demonstrate that Sr2InTaO6: Mn4+ (abbreviated as SITO: Mn4+), a phosphor emitting far-red light, can be used to fabricate light-emitting diodes (LEDs) for plant cultivation. SITO: Mn4+ phosphor contains two unique excitation peaks at 325 and 368 nm that can be excited efficiently by near-ultraviolet light. The SITO: Mn4+ phosphor generates far-red light with a peak wavelength of 695 nm at an excitation wavelength of 368 nm. The optimal Mn4+ ions doping concentration was investigated. Furthermore, red LEDs were prepared through the combination of 365-nm chips and SITO: Mn4+ phosphors and they emitted bright far-red light at 20–100 mA current. As a result, SITO: Mn4+ phosphors can be used in the production of LEDs for plant cultivation illumination.

Benefits of using TiO2 quantum dots in producing low-cost and high-quality white light-emitting diodes

Quantum dots (QDs) is considered as a potential material for the improvement of light-emitting diodes (LEDs). However, different from the traditional phosphor materials, they have unique scattering and absorption properties affected by their several nanometers sizes, which makes their application in the production of LED confront more challenges. In addition to this, their influences on QDs-converted LEDs (QCLEDs) are rarely investigated. So as to propose solutions for those problems, in this article, we experimentally and theoretically investigated the impacts of titanium dioxide (TiO 2 )QDs’ scattering and absorption on the light quality of QCLEDs by drawing a thorough comparison between their properties and the traditional yttrium aluminum garnet phosphors characteristics. The outcomes showed that QCLEDs have poor radiant efficacy and stability due to QDs’ strong characteristic of absorption (reabsorption) while their weak scattering property causes a low uniformity in correlated color temperature (CCT). For achieving high efficiency and stability white LEDs, we highly suggest using QDs with a low concentration to get reductions in the reabsorption and total internal reflection losses. With 0.05 concentration of TiO 2 nanoparticles (TiO 2 NPs), the white LEDs can simultaneously achieve a high CCT (approximately 7500 K) and a high color rendering index (around 85).

Highly Stable and Efficient Mn2+ Doping Zero-Dimension Cs2ZnxPb1-xCl4 Alloyed Nanorods toward White Electroluminescent Light-Emitting Diodes.

Zero-dimensional (0D) crystal structure perovskite NCs have reemerged as promising materials owing to their superior long-term stability; however, their poor conductivity leads to the inferior electrical performances and critically restricts the optoelectronic application of 0D perovskite materials. Herien, the alloyed 0D crystal structure Cs2ZnxPb1-xCl4 nanorods (NRs) have been synthesized by the modified hot-injection method, which emits bright blue-violet light at 408 nm, and the optimized photoluminescence quantum yield (PLQY) reaches 26%. The Cs2Zn0.88Pb0.12Cl4 NRs display more excellent air stability and an order of magnitude higher conductivity than CsPbCl3 nanocube films. In addition, we dope Mn2+ ions into the Cs2Zn0.88Pb0.12Cl4 NRs, which accomplished the optimized PLQY of 40.3% and polarized emission with r = 0.19. The light-emitting diodes (LEDs) based on Mn2+ ion doped Cs2Zn0.88Pb0.12Cl4 NRs exhibit a chromaticity coordinate (CIE) of (0.36, 0.33), an EQE of 0.3%, and a maximum luminance of 98 cd m-2. This work has enriched ideas for the production of white light perovskite LEDs.

Criticality assessment of metal resources for light-emitting diode (LED) production – A case study in China

Understanding the importance of raw materials is crucial for ensuring high material efficiency in industrial production processes. A common criticality assessment of resources is usually a top view on their supply risk and economic importance. This cannot directly be integrated in a specific process for material manufacturing, which is in high demand to identify the importance of a resource for the process and implement process optimization. In this study, a parameter named resource recirculation factor is introduced, and the criticality assessment model is reformed to facilitate the evaluation of the LED production process from substrate preparation to lamp manufacture. 22 types of materials were selected for evaluation with material flow analysis. The criticalities of gallium and indium, with values of 159.33 and 24.18, were found to be the largest owning to their high supply risk and environmental risk values, which were significantly higher than those of the other materials, such as copper (0.01) and iron (0.27). The high criticality of gallium resulting in trimethyl gallium being the most important material, while trimethyl indium and indium tin oxide (ITO) etchant ranked second and third, respectively. Based on the comparison of the production sections, the epitaxial growth and chip fabrication compressed the two most important sections, which were closely related to the critical metals. Under comprehensive environmental evaluation, the environmental impact of LED production sections was in the order of chip fabrication > substrate preparation > lamp manufacture. The proposed criticality assessment method can provide a basis for the material evaluation and cleaner production of industrial production processes, where comprehensive environmental evaluation can also contribute to the criticality evaluation. • Resource recirculation factor is introduced to criticality assessment model. • Light-emitting diode (LED) production processes were evaluated. • Comprehensive environmental assessment analyzed environmental impact of the waste.

Self‐Assembled Nanowrinkle‐Network‐Structured Transparent Conductive Zinc Oxide for High‐Efficiency Inorganic Light‐Emitting Diodes

AbstractA ZnO nanowrinkle network (NWN) film is applied as a transparent conductive electrode (TCE) to improve the light extraction efficiency of inorganic light‐emitting diodes (LEDs). The NWN structures in sol–gel‐derived ZnO films are spontaneously formed by the evaporation of the solvent during prebaking to achieve the gelation of the sol–gel ZnO film. Despite the NWN structure, the optical transmittance of the NWN‐ZnO film prebaked at 130 °C is maintained at ≈92% with respect to that of unmodified glass. However, the optical transmittance of the NWN‐ZnO film prebaked at 150 °C is significantly decreased because of the increase in nanowrinkle density. As a result, the electroluminescence intensity of LEDs having the NWN‐ZnO TCEs increases significantly for the samples prebaked at temperatures up to 130 °C but decreases slightly in those treated at 150 °C. In addition, LEDs having the NWN‐ZnO film show enhanced spectral distribution over wide angles, which is important for lighting applications. On the basis of these results, the spontaneously assembled NWN‐ZnO films formed by the sol–gel method show potential for the low‐cost production of inorganic LEDs having high light extraction efficiencies.

Quantum dots synthetization and future prospect applications

Abstract Quantum dots (QDs) are nanocrystals of a semiconductor material that exist in a size regime less than 10 nm. QDs have become promising nanoparticles for a wide variety of different applications. However, the major drawback of QDs is their potential toxicity. This review reports on some recent methods for the synthesis of QDs and explores their properties, structures, applications, and toxicity. QDs are extraordinary because their minute size produces a physically confined electron cloud, an effect known as the quantum confinement. Certainly, because of their special properties as they had a great unique optical, electronic, and chemical properties that were not observe in other materials. These unique properties of the QD are an attractive material for a variety of scientific and commercial applications, most of them recently been realized, such as biosensors, bioimaging, photodetectors, displays, solar cells, wastewater treatment, and quantum computers. Finally, but not the end, an interesting potential QD application in future perspectives will expect as light-emitting diode products, biomedical applications, and Li-Fi.

Benefits of using TiO2 Quantum Dots in producing low-cost and high-quality white LEDs

Quantum dots (QDs) is considered as a potential material for the improvement of light-emitting diodes (LEDs). However, different from the traditional phosphor materials, they have unique scattering and absorption properties affected by their several nanometers sizes, which makes their application in the production of LED confronts more challenges. In addition to this, the influence of QDs on QDs-converted LEDs (QCLEDs) is barely studied. In order to propose solutions for those problems, in this article, we carried out experimental and theoretical investigation of the effect of TiO 2 QDs’ scattering and absorption on the optical performance of QCLEDs by comparing their properties with the traditional yttrium aluminum garnet phosphors’. The results showed that the strong absorption (reabsorption) of QDs is the cause of low radiant efficacy and stability of QCLEDs, and their weak scattering ability results in a low color homogeneity. For achieving high efficiency and stability white LEDs, we highly suggest using a low QD concentration to get reductions in the reabsorption loss and the total internal reflection loss. With 0.05 concentration of TiO 2 NPs, the white LEDs can achieve a high CCT of ∼ 7500 K and a high CRI of ∼ 85 simultaneously. Moreover, this TiO 2 concentration can also increase the luminous intensity by ∼ 31%. Therefore, we believe that the study can propose a potential approach to the production of low-cost CDs-based LEDs with high performance in a near future.

A study of copper–tungsten oxide materials for photovoltaic application

Purpose Even though copper–tungsten has shown signs of potentials, relatively little is currently known about its appropriateness for photovoltaic application. This paper aims to evaluate the suitability of copper-tungs oxides as photovoltaic absorbers while investigating the consequences of oxygen content variation. Design/methodology/approach Using profilometry, Hall measurements, Seebeck test and spectrophotometry, grown samples were defined. Samples of 5 standard cubic centimeters per minute (sccm) and 7 sccm exhibited appropriate characteristics and were further tested using personal computer one dimension (PC1D) computational simulation at the system stage. To grow materials with an average thickness below 0.45 µm, magnetron co-sputtering was used. Three sample sets, varied by oxygen flow rate, were made with flow rates of 5sccm, 7sccm and 9sccm, respectively. Findings Some samples proved to be effective absorbers, using a cadmium telluride device as the criterion of output calculation, with one sample chosen as ideal for each type of flow rate. For the chosen samples, an optimum thickness was also obtained, i. It was discovered that thinner cells, optimal for both groups with 0.6 µm, performed better to than other thicknesses. Research limitations/implications The material also demonstrated prospects for applications in window layers, but more needs to be known. Practical implications Thin film material properties and their operating processes are relatively complex, so it is important to find simple and cost-effective ways to forecast performance. While relatively new, numerical modeling has proven to be very useful in defining the critical properties of thin film devices, thereby helpful for predictions of performance. Solar cell capacitance simulator one dimension, amorphous semiconductor analysis, personal computer one dimension (PC1D), analysis of micro-electronic and photonic structures and automat for simulation for heterostructures (33) are several common models in the thin film industry. Due to its availability and relative ease of use, PC1D was used in this project. Social implications As the search for the balance among performance, cost, reliability and availability continue, more absorber components continue to evolve, notably from the chalcogenides. Because of their ability to absorb light, ternary transition metal chalcogenides are useful in the production of hydrogen and in the energy storage sector, as well as in the production of light-emitting diodes and solar photovoltaic (PV). Originality/value There are several methods for the manufacture of copper–tungsten alloys, but the process of combinatorial sputtering of magnetrons provides satisfactory results even for the manufacture of various other materials. Cu2WSe4, an excellent alternative to sputtering, is one of the very few copper–tungsten selenide materials tested, synthesized by hot simple injection to have strong crystallinity and lacks impurity. The optical properties of colloidal Cu2WSe4 show that Schottky diode–like behaviors are present in the material, suggesting its potential for use in solar cells. Cu-W alloys could have a lot more to give the PV industry, by all indications. Further exploration of the oxides by this work is thus justified. Transparent conducting oxides, interfacial layers or charge-transporting compounds are commonly used as transition metal oxides. Nevertheless, as absorbers, metal oxides such as BiFeO3 and the traditionally highly studied Cu2O have been tested, with Cu2O showing a conversion efficiency of up to 10% under particular conditions. This displays strong electronic and optical properties, so there might be some possibility of studying other PV absorption metal oxides. The optical properties of colloidal Cu2WSe4 show that Schottky diode–like behaviors are present in the material, suggesting its potential for use in solar cells.

Deep machine learning of the spectral power distribution of the LED system with multiple degradation mechanisms

Abstract The performance and reliability of the light-emitting diode (LED) system significantly depend on the thermal–mechanical loading-enhanced multiple degradation mechanisms and their interactions. The complexity of the LED system restricts the theoretical understanding of the root causes of the luminous fluctuation or the establishment of the direct correlation between the thermal aging loading and the luminous outputs. This paper applies the deep machine learning techniques and develops a gated network with the two-step learning algorithm to build the empirical relationship between the design parameters and the thermal aging loading and the luminous output of LED products. The flexibility of the proposed method will be demonstrated by integrating it with different neural network architectures. The proposed gated network concept has been validated in both multiple LED chip packaging and LED luminaire under thermal aging loading. The validation of the luminous data of multiple LED chip packaging shows that the maximum differences of the correlated color temperature (CCT) and color coordinate are 2.6% and 1.0%, respectively. Moreover, the machine learning results of the LED luminaire exhibit that the differences of lumen depreciation, CCT and color coordinate are 1.6%, 1.9% and 1.1%, after 2160 h of thermal aging.

Evaluation of resource use in the household lighting sector in Malaysia considering land disturbances through mining activities

This study evaluated resource use in the household lighting sector in Malaysia from the perspective of the lifecycle of the resources using the concept of total material requirement (TMR), which represents the scale of land disturbances caused by mining activities for resource exploitation. The TMR of incandescent bulbs (INC), compact fluorescent lamps (CFL) and light-emitting diode (LED) bulbs is evaluated during the production and operation stages. Then, the flow and stock of different lighting technologies in the Malaysian household sector during the period 2015–2050 is estimated considering two scenarios based on the rapidity of transition of lighting technologies in Malaysian society. Finally, the overall resource use of the household lighting sector in Malaysia during 2015–2050 is examined, considering the uncertainties of the lifespan of light bulbs and power generation. Although our findings indicate that the TMR of the LED production was the highest of all three types of light bulb, the high energy efficiency of LED bulbs makes the total TMR of LED the lowest among the three types of lighting evaluated after 700 operational hours. In the case of infrequently used light bulbs, the CFL may be superior to LED in the context of resource use. Survey results for Malaysia in 2020 indicated that only 13% of total obsolete household light bulbs are properly treated and recycled. It was also found that the quick transition of lighting technologies will avoid significant resource exploitation, and that the year 2025 is a milestone for natural resource use and recycling in Malaysia.

Quality safety monitoring of LED chips using deep learning-based vision inspection methods

The surface quality safety inspection of a light-emitting diodes (LED) chip is an indispensable step in the LED production process. The traditional vision inspection algorithm extracts defect features by artificial feature extraction. This method has become increasingly difficult as chips have become more miniaturized, and it is difficult to meet the quality safety requirements. Recently, machine learning-based vision detection methods, especially the models of deep convolution neural network (CNN), have made significant breakthroughs in this field, and their performances greatly exceed the traditional model based on manual features. In this paper, a parallel deep convolution model parallel spatial pyramid pooling network (PSPP-net) for LED chip surface quality detection is proposed. Specifically, this model aims at utilizing the advantages of the spatial pyramid pooling (SPP-net) model to online and offline extract two groups of depth-based CNN features through offline training and online recognition of two depth-based CNN data conversion streams. Then, the features are mixed and intersected in the GPU to form 1024-dimensional image feature vectors. Finally, softmax regression is adopted for defect classification and recognition. The problem of off-line feature training extraction and on-line defect recognition in surface quality safety inspection of LED chips is solved.

9‐2: Manufacturing Process for Mass Production of Micro‐LED Displays and High‐Speed and High‐Yield Laser Lift‐Off Systems

In our previous work, we proposed and evaluated processes and equipment to facilitate the mass production of micro LED (light emitting diode) displays. The new technologies include LLO (laser lift off), mass‐transfer, color conversion and backplane with micro Si chip. We quantitatively evaluated them and report results.

Effects of silicone lens aging on degradation kinetics of light-emitting diode package in various accelerated testing

Silicone is commonly used in light-emitting diode (LED) package as lens and/or encapsulation owing to its high light transmittance, large refractive index, and good thermal stability. However, the effect of silicone lens aging on the lumen decay and color shift of LED package is a considerable concern for package level reliability. This study empirically investigates the effects of silicone lens aging on lumen decay and color shift of LED package under three accelerated tests, namely, the constant stress-accelerated degradation test, step-up stress-accelerated degradation test, and step-down stress-accelerated degradation test (SDSADT). Results reveal that silicone lens aging substantially contributed to lumen decay and color shift of LEDs and considerably influenced the degradation kinetics of LED package. The color coordinates of LED package covered with aged silicone specimen in three testing methods exhibit a steady yellowing shift law at the same 45-degree direction. Silicone lens aging primarily reduces its transmittance to blue light as accumulated thermal oxidation and hydrolysis reaction, and its effect on the blue peak intensity of LED is independent of the stress-loaded order of step stress-accelerated degradation testing (SSADT). In addition, the effect law of silicone lens aging on LED lumen and color shift could be presented with the exponential and power function models, respectively. Lumen decay and color shift are mostly independent of the historical stress and loaded order in SSADT. The SDSADT testing manner more effectively distinguishes the color shift effect of thermal stress level compared with other accelerated tests. These findings are assumed to benefit the design and reliability assessment of LED products.

Factors Affecting the Consumption of Energy-Efficient Lighting Products: Exploring Purchase Behaviors of Thai Consumers

The continued usage of inefficient lighting products in residential sectors is one of the major causes of the rapid growth in global energy consumption. Their replacement with highly efficient lighting appliances could avoid large amounts of electricity consumption and reduce CO2 emissions worldwide. In this regard, the collective contribution by the residential sector is extremely important and the increase in demand for energy-efficient lighting products can help achieve sustainability goals. This study aims to examine the determinants of household consumers’ behaviors in purchasing energy-saving lighting products by applying the Theory of Planned Behavior (TPB) as the main theoretical framework. Data (n = 288) from a survey in Thailand were analyzed using causal Structural Equation Modeling (SEM). The results suggested that attitude has the largest direct effect, while subjective norm was the weakest predictor of purchase intention towards light-emitting diode (LED) products. In addition, this study expands the TPB by including an investigation of a direct effect of attitude on purchase behavior. The results suggest that attitudes have a strong direct influence on the purchasing behavior for LED products. Additionally, only some socio-demographic variables have significant effects on purchase behavior. The study’s findings highlight several implications for policymakers, the private sector, and green marketers in developing practical strategies. Furthermore, suggestions and future research directions are discussed.

Bluetooth embedded digital ammeter with android app data logging

Monitoring current supplies to light emitting diode (LED) luminaires is one of the reliability tests performed manually. Bluetooth (HC-05) embedded digital ammeter was proposed to acquire currents of a badge of LED products and hence, quality can be assured. Android App was designed to remotely record the current supplies to the different models of LED products and checking if the current measured is within the allowed range. The current data can be further analysed to control the quality of the LED luminaires produced. The pass and fail-current range can be set in the digital ammeter for alerting abnormal current measured by the operator. Therefore, IOT embedded digital ammeter will help in monitoring data consistency of LED products and improve quality assurance procedure.

Review— Toyoda Gosei's History of R&D on Blue LEDs with Professor Isamu Akasaki

Toyoda Gosei (TG) started joint R&D with Prof. Akasaki and Prof. Amano (collectively, the Akasaki Group) in 1986, immediately after the Akasaki Group succeeded in the growth of high-quality GaN single crystals for the first time in the world. Then, the Akasaki Group and TG concluded an entrustment R&D agreement with Japan Science and Technology Agency (JST) in 1987 to promote R&D through the investment of JST. Under these circumstances, the Akasaki Group achieved the growth of high-quality p-type GaN and n-type GaN, believed impossible at that time. These breakthrough technologies were of fundamental importance for developing blue light-emitting diodes (LEDs). Namely, (1) high-quality GaN single crystals, (2) p-type GaN, and (3) n-type GaN were found to be applicable to industrial products. Thanks to the Akasaki Group, TG started the mass production of blue LEDs in 1995. However, at that time, these LEDs were not particularly bright, and no one believed that they would be used in general lighting. In spite of this prediction, the brightness of blue LEDs was improved markedly by industry-based developments, leading to their widespread adoption in many applications.

COLOR AND SPECTRAL CHARACTERISTICS OF WHITE LIGHT EMITTING DIODES AND THEIR VARIATION DURING AGING

The relation between numerical values of photometric characteristics (total luminous flux TLF, correlated color temperature CCT, color rendering index CRI) of white light emitting diodes (LED) and the variation of the spectral shape of their radiation during aging has been investigated. All the measurements were made on internationally adopted test methods, taking into account environmental conditions, electrical parameters and evaluated measurement uncertainty. Every piece of test and measurement equipment has actual verification or calibration with traceability to national and international references. It was demonstrated that in the luminescence spectra consisting of the “blue” band around 450 nm originating from the semiconductor heterostructure, and the broad “yellow” band from luminophor, the last band is nonelementary and consists of at least two bands: the “green” one around 530 nm and the “orange” one around 580 nm. The most unstable “green” band has the highest impact on photometric characteristics. As a consequence, further investigation should be performed on how instability of elementary bands and its quantity will link not only with photometric characteristics, but with production conditions and material properties of LED heterostructure and luminophor itself. In particular, for improvement of the color stability of white LED, the parameters of luminophor forming the “green” band should be stabilized. А unified method for accelerated testing of LED products and method for long-time lifetime prediction shall be developed, taking into account not only depreciation of TLF, but also shift of other photometric and spectral characteristics of white LED.