Modeling Equivalent Leds Source And Designing Lens For Uniform Illumination And Color Distribution

Due to theirs compact size, energy conservation, environment protection and long life soon, light emitting diodes (LEDs) have been widely used in many illumination fields such asstreet lighting, read lighting and indoor lighting etc.. Generally, the luminous intensitydistribution of a LED approximates Lambert distribution. If the LED is used to illuminate thetarget plane directly, a non-uniform irradiance distribution is generated on the target plane. Inorder to improve the uniformity of LED illumination, secondary lens is often used toredistribute the flux from the LED. For secondary lens design, modeling a precision LEDsource is quite important. In this thesis, we combine the BP neural network and simulatedannealing algorithm together to find the optimal parameters for modeling the equivalent LEDsource. The combined algorithm can model not only LED source with single wavelength butalso white LED source. Based on the white LED source, we design a free-form lens whichmakes the output light of LED to generate uniform irradiance and color distribution on thetarget plane. Some important research works and conclusions are listed as following:We propose a new method which can be employed to seek the optimal parameters forequivalent LED source with single wavelength. The BP neural network is used to build theimplicit function relationship between the LED chip parameters and the luminous intensityprofile basing on a large number of known data. An evaluation function is constructed toreflect the closeness between the luminous intensity of LED model and that of actual LED.The smaller the value of evaluation function, the closer the intensity distribution of LEDmodel and that of actual LED is. A simulated annealing algorithm is used to seek theminimum of the evaluation function. By the method, we model two LED sources which aremanufactured by OSRAM. The results show that the NCCs of intensity distribution of bothmodels with the actual LED are both more than99%.We also analyze the influence of phosphor thickness and concentration on the angledependent correlated color temperature (ADCCT). By using the method above, it is easy tofind the optimal thickness and concentration which make the LED model produce the closeADCCT with the actual LED. We model an equivalent LED source according to theREFOND LED3535ADCCT. The NCC of the intensity distribution between the equivalentLED and the actual chip is about99.1%. In addition, we also model an equivalent complexLED source which is highly close to the REFOND LED3535in luminous intensity profileand ADCCT. The results show that the NCC of the intensity distribution and ADCCT betweenLED model and actual LED are97.5%and97.5%, respectively. The complex LED sourcemodel can be used as white LED source in secondary lens design.With the equivalent complex LED model, we design a lens which makes the emittinglight from LED form a uniform irradiance and color distribution on target plane. The lens is afree-form lens consisting of one free-form surface (outside surface) and one spherical surface(inside surface). Because of the rotational-symmetrical structure of the lens, we only take intoaccount the cross-section profile shape in design. The cross-section profile corresponding tothe free-form surface is set as a cubic spline curve. The initial configuration of lens is reallyimportant for the lens design. Therefore, we adjust the spline curve shape at beginning manually so that the initial lens can form an as uniform as possible irradiance and colordistribution. Then the interactive optimization module in TracePro is used to optimize the lensfor the desired irradiance and color distribution on target plane. By the ray-trace of theoptimized lens, it is shown that the uniformity of the irradiance and color distribution are93and91%, respectively. Compared to the initial lens, the optimized lens has an improvement ofabout17%and8%in irradiance and color distribution.