| dc.description.abstract | In this thesis, we will propose a method of optical field calculation to accurately calculate the source-to-source spacing and the source-to-reflective-plane spacing of the extended source to obtain uniform illumination into the target plane. A light spread function (LSF) that is composed of a two-term Gaussian function from nonlinear least squares method will be utilized to simulate the illuminance and irradiance distribution of each extended source on the target plane. The LSF will be a function of the illuminance and distance, and the illuminance of the source on the target plane can be derived using the LSF. In the optical system, the energy of the mirror reflected rays can be approximated using a virtual source. Under various arrangement conditions in the optical system, when comparing the results of LSF and optical design software for the entire target plane, the mean absolute percentage error (MAPE) can be lower than 1.5%. The effect of the rays reflected by the sides of a reflective plane and a corner reflective plane was also considered and calculated using the LSF. When comparing the results calculated using the LSF method for the entire target plane with the results from the optical design software, the MAPE can be lower than 1.0%.
Furthermore, to verify the feasibility of illuminance and irradiance calculation for the optical system, a direct backlight unit (DBLU), a step-and-repeat collimated exposure and a scanning collimated exposure were designed using the calculated spacing. Consider a DBLU with 36 batwing sources in a rectangular arrangement with a backlight box thickness of 20 mm. The reflectivity of the backlight box is 0.9. We calculated the uniformity of 9 points without adding any optical films. The illuminance uniformity from LSF was 99.25%. After assembling a prototype of the DBLU with the same parameters, the illuminance uniformity was found to be 96.68%. When comparing the results from the LSF and measured data at y = x and x axis for the DBLU, the MAPE values were 0.92% and 0.46%, respectively. The collimated exposure were designed by the calculated rotation angle of light source and tilt angle of reflective plane. After simulating by the optical design software, the average irradiance and the half angle of radiant intensity can achieve the demand of collimated exposure, and the irradiance uniformity was better than 97%. It is apparent that in the design of a thin DBLU, the LSF calculation provides a more precise design method, which enables designers to simply choose sources and arrangement patterns according to the requirements of an optical system.
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