Light emitting dioxides (LEDs) would inevitably replace the incandescent lamps and dominate the lighting market. There is a growing demand for LED measurement and calibration. However, using the incandescent lamp as a standard lamp to measure LEDs would produce great uncertainty. LED filament standard lamps for total luminous flux and luminous intensity are developed to solve this problem. Both the intensity of type A and type B standard LED for luminous flux are uniformly distributed over 4π geometry. The angular uniformity and conformity of the inverse square law of the standard LED for luminous intensity are well satisfied. The developed LED standard have a shorter warm-up time, good short-term stability and repeatability. The luminous flux and luminous intensity are increased by 1.5% ~ 2.5% after 2000 hours aging.
To measure the total luminous flux emitted by a light source, the standard lamp which provides an absolute value of the total luminous flux is used with a sphere-photometer. Many institutes have developed their standard lamps based on LED. However, it is difficult to acquire uniform light distribution like the traditional incandescent lamps. To solve this problem, a novel LED filament standard lamp for total luminous flux is developed. First, a luminous intensity distribution model of a single LED filament is established. Based on this model, a method to calculate the luminous intensity distribution of multiple LED filaments is derived. To evaluate the uniformity of a light source, a spatial distribution uniformity index is introduced. Second, the spatial distribution uniformity index of the developed standard lamp is calculated by simulation and the optimal design is obtained. Experiment shows that the LED filament standard lamp for total luminous flux with the optimal design obtained uniform luminous intensity distribution in 4π geometry.
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