A precise model of LED lighting and its application in uniform illumination system

Abstract

Tianjin University of Technology and Springer-Verlag Berlin Heidelberg 2011 C Optical models directly effect the irradiance distribution of observed surface. Traditionally, approximate Lambertian models are widely used in designing the light-emitting diodes (LED) arrays in spite of their errors compared with the experimental data. But now a novel LED optical model for uniform illumination system has been proposed, in which the curvefitting technique is used to reduce the inherited errors and modify those previous models. The points from the curve of the LED light intensity are adopted, and a spline curve is designed for fitting, which obtains the revised mode. To verify its feasibility, we apply the new model in a 4 4 array design. The results show that compared with the approximate Lambertian, the light intensity distribution produced by the fitting model is more uniform and intense, as is expected.Light-emitting diodes (LEDs) lighting, with merits of saving energy, longer life and environment protection, has a wide application foreground. As an important technique innovation for lighting LEDs will replace the traditional incandescent, fluorescent and gas discharge lamps, and become dominant in lighting market in the foreseeable future. LEDs have many favorable characteristics, including small volume, lower power consumption, instant power-on capacity, and absence of mercury or any other form of toxic substance [1][2][3] . For the improvements in the luminous flux, LEDs are used in new applications, such as indoor plant cultivation [4] , displays [5] and biomedicine [6] . However, though the luminous flux of every modern high-power LED is up to 150 lm, several LEDs cannot produce a practical power without permutation and combination. Therefore, the arrangement of the LED must be designed reasonably, otherwise it will cause glare and wasted energy. The perceived illumination uniformity depends on the factors such as the distance from the observed surface to the target field, the optical models of the light sources, background luminance, and reflectance, pattern and color of target. Typically, a single LED is optically modeled on realistic numerical models or on measurementbased models [7][8][9][10] . Among them, Moreno proposed approximate Lambertian models to achieve uniform irraduance distribution efficiently [11,12] . Using these models, we are able to obtain parameters, which provide the maximum LED density and the minimum LED-to-detector distance for different LED arrays, which produce satisfactory uniformity.However, it is doubtful that the irradiance distribution of the model used in approximate Lambertian is consistent with the actual LED or not. And we did find certain deviations by comparing the irradiance distributions of approximate Lambertian model and actual LED. In this paper, we propose a new model, which uses curve fitting method to amend the LED luminescent model. The model is not only useful in LED lighting design, but also helpful in package design. The optical simulation of LED arrays by rele...

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