Secondary Lens Optimization for LED Lamps

The purpose of this paper is to present a methodology for optimizing the geometry of the LED （light emitting diode） secondary lens. The research objective is to uniform the illumination distribution on a target plane for nonimaging application. In order to achieve this, a software that simulates ray tracing is used, in conjunction with a heuristic process for enhancing the optimized parameters that form the geometry of the LED secondary lens. Spherical lenses was opted for optimization due to its lower manufacture complexity.

The establishment of reliability model for LED lamps

In order to verify which of the distributions and established methods of reliability model are more suitable for the analysis of the accelerated aging of LED lamp, three established methods （approximate method, analytical method and two-stage method） of reliability model are used to analyze the experimental data under the condition of the Weibull distribution and Lognormal distribution, in this paper. Ten LED lamps are selected for the accelerated aging experiment and the luminous fluxes are measured at an accelerated aging temperature. AIC information criterion is adopted in the evaluation of the models. The results show that the accuracies of the analytical method and the two-stage method are higher than that of the approximation method, with the widths of confidence intervals of unknown parameters of the reliability model being the smallest for the two-stage method. In a comparison between the two types of distributions, the accuracies are nearly identical.

Determination of cut-off time of accelerated aging test under temperature stress for LED lamps

To acquire a rational minimum cut-off time and the precision of lifetime prediction with respect to cut-off time for the accelerated aging test of LED lamps, fifth-order moving average error estimation is adopted in this paper. Eighteen LED lamps from the same batch are selected for two accelerated aging tests, with 10 samples at 80 ℃ and eight samples at 85 ℃. First, the accelerated lifetime of each lamp is acquired by exponential fitting of the lumen maintenances of the lamp for a certain cut-offtime With the acquired lifetimes of all lamps, the two-parameter Weibull distribution of the failure probability is obtained, and the medium lifetime is calculated. Then, the precision of the medium lifetime prediction for different cut-off times is obtained by moving average error estimation. It is shown that there exists a minimum cut-off time for the accelerated aging test, which can be determined by the variation of the moving average error versus the cut-offtime. When the cut-off time is less than this value, the lifetime estimation is irrational. For a given cut-off time, the precision of lifetime prediction can be computed by average error evaluation, and the error of lifetime estimation decreases gradually as the cut-off time- increases. The minimum cut-off time and medium lifetime of LED lamps are both sensitive to thermal stress. The minimum cut-off time is 1104 h with the lifetime esti- mation error of 1.15% for the test at 80 ~C, and 936 h with the lifetime estimation error of 1.24% for the test at 85 ℃. With the lifetime estimation error of about 0.46%, the median lifetimes are 7310 h and 4598 h for the tests at 80 ℃ and 85℃, respectively.

Development of the Operating Circuit for a LED Lamp Based on the Cockcroft-Walton Circuit

The operating circuits for LED （light emitting diode） lamp composed of diodes and DC capacitors only are proposed. The proposed circuit is based on a double-voltage rectifier circuit and a Cockcroft-Walton circuit. The circuit can operate LED without flicker, and is free from switching noise since high frequency switching circuit is not used. To replace an AC capacitor by a DC capacitor for the ballast, a diode is connected across the capacitor in parallel, and the operating voltage of LED unit is kept at the value greater than the peak voltage of the input power source. The circuit realizes high efficiency and high input power factor compared with the operating circuits on the market. Cockcroft-Walton-type circuit can operate many LED devices in series connection. Series connection is preferable for fabricating LED unit of a constant voltage characteristic. Moreover, fairly flat waveform of LED operating current is realized by Cockcrofl-Walton-type circuit, even though capacitor ballast is used.

Lamp Distribution Design for Adjustment of Florescence in Floral Production

[Objective] The aim was to introduce characters of light sources and select the optimal lamp scheme for floral production in greenhouses. [Method] With chrysanthemum cuttings as materials, HPSL, energy-saving fluorescent lamp, and LED agricultural lamp were made use of to carry out field tests in order to compare practical effects according to light characters of different lamps and plant growth de-mands. [Result] The results show that LED lamp performed the best of the three in practical use. LED square lamp designed in bat-wing shape would be the most ben-eficial for lamp distribution in a greenhouse. [Conclusion] LED agricultural lamp is the most popular currently, for it is energy saving and easy for operation.

The effectiveness of light emitting diode(LED)lamps in the offshore purse seine fishery in Vietnam

Fishing with artificial light has become one of the most advanced,efficient,and common methods for the night-time purse seining in Vietnam.This study evaluated the radiation spectrum,CIE chromaticity coordinates,correlated color temperature(CCT),catch rate,fuel consumption,and CO_(2)emissions when using Light emitting diode(LED)lamps(0.196 kW)in comparison with the use of metal halide(MH)lights(1 kW)in the offshore purse seine fishery in Quang Tri province,Vietnam.The fishing efficiency of the purse seine fishing boats using LED lamps has increased 1.58 times in catch rate than MH lights,although the energy consumption of LED lamp is 4 times smaller.Fuel consumption of boats per trip using LED lamps was one third of that using MH lights.The use of LED reduced the radiation spectrum,especially the intense UV radiation which negatively affects the health of fishermen.This study also showed the potential of CO_(2)emission reduction up to 1.09 tons of CO_(2)per trip per boat from the use of LED lamps in the offshore purse seine fishing boats.

Thermal design for the high-power LED lamp

This paper summarizes different kinds of heat sinks on the market for high power LED lamps. Analysis is made on the thermal model of LED, PCB and heat sink separately with a simplified mode provided. Two examples of simulation are illustrated as a demonstration for the thermal simulation as guidance for LED lamp design.