Luminous Property Analyses And Testings Of The LED Phosphor

Coating the LED chips with phosphor constitutes the major method to realize white LED lighting. The performance of LED phosphor directly determines the luminous property of WLED (white-light LED). Therefore, it is the core issue to analyze and evaluate performances of phosphors accurately and excavate lighting properties of those phosphors in depth. In practical daily lightings, the luminous efficacy, chromaticity and thermal effect etc. are of major concerns. The luminous efficacy, chromaticity and spatial light-intensity distribution of WLED can be altered by varying the particle size, thickness, shape and positions among others. In this dissertation, systematic researches concentrating on lighting properties of various phosphors have been carried out, emphasizing on optical-property analyses of conventional phosphor packaged LED and remote phosphor packaged LED. This dissertation comprises of several parts as follows:a) Elucidations of the phosphor classification, development history, lighting mechanism, characterizations, applications, traditional measurement methods, and lighting performance evaluation of WLED.b) Proposal of an integrating sphere based performance testing system and method for blue-light LED stimulating phosphors. The proposed method is capable of reflecting the phosphor lighting property under practical functioning circumstances and measuring the phosphor lighting performance accurately, freeing from various shortcomings of traditional measurement methods. This proposed method characterizes higher reliabilities, easier implementations and minor errors. Moreover, the lighting performance and spectral power distribution of phosphor under different driving currents can be obtained. Results demonstrate the feasibility of the proposed measurement system and analytic method in characterizing phosphor lighting performances. Optimal combinations of phosphor and LED chips can be achieved by adjusting currents. Additionally, the system is designed with excellent expansibility, which satisfies different demands of phosphors, i.e. the ultraviolet stimulating oriented RGB phosphor, via fitting different LED stimulating sources.c) Characterizations of the luminous efficacy, quantum efficiency, light conversion efficiency, correlated color temperature (CCT) and light intensity distribution of conventional WLED and remote phosphor WLED. The integrating sphere, spectrometer and light-intensity distribution detector etc. are utilized in the investigations of the influences brought by different packages on WLED performances under different currents and temperatures. Advantages and disadvantages of diverse packages are also discussed. From the experimental results, it can be drawn that the quantum efficiency, light conversion efficiency and CCT of remote phosphor WLED vary slower than those of the traditional WLED with the ascending currents and temperatures under same experimental conditions. Moreover, remote phosphor WLED possesses better Y/B ratio spatial distribution homogeneities. From observations of light-intensity distributions resulting from different stimulating sources, it can be concluded that stimulating sources are irrelevant to light-intensity distributions, and phosphor shapes may adjust the light-intensity distributions. Therefore, phosphor shapes can be specifically designed for expected light spot patterns.d) Researches focusing on the light performance differences of both high and low CCT crown-shaped remote phosphor WLED under diverse currents and temperatures. The CCT differences greatly influence the luminous efficacy of the whole WLED. Experimental results suggest:the peak wavelengths slide towards the shorter-wavelength direction in the spectrum under large currents due to the quantum confinement stark effect in the LED active layer, departing away from the optimal stimulating wavelength of high CCT phosphors and approaching that of low CCT phosphors. The luminous efficacy of high CCT phosphor thus decreases, while that of low CCT phosphor increases. The behavior of CCT of those two distinct phosphor conveys contrary trends. The luminous efficacy and CCT variations of different phosphors is strongly related to the chromatic coordination drift caused by quantum efficiency variations. The quantum efficiency and luminous efficacy of both high and low CCT LED slightly increase with the ascending heat-sink temperature. Regarding high CCT LED, the quantum efficacy and luminous efficacy decrease with the ascending currents, being contrary to the case of low CCT LED. The high CCT LED has better performances in lighting properties but less chroma-characterization stabilities than the low CCT LED.e) Details of a newly-designed remote phosphor packaged LED system. The package, within which the phosphor slice isolates from the blue-light LED chip, is designed along with a reflector. The lighting performances of this and traditional remote phosphor packaged LED system are compared. The comparison indicates that the proposed system is capable of enhancing the luminous performance of the whole LED system, reducing the systematic CCT, and producing high CCT spatial distribution homogeneities. Lighting mechanisms of those distinct systems are analyzed in detail to explain the essence of luminous performance improvements with the proposed system. Advantages and application values over traditional remote phosphor packaged LED systems are sufficiently proven by experiments.