Design of Direct LED Backlighting Based on an Analytical Method of Uniform Illumination

A direct LED backlight unit (DLBLU) with extended sources based on an analytical design method of uniform illumination is investigated. We developed an analytical calculation method of the light spread function (LSF) for achieving highly uniform illumination into the diffuser plate (target plane) of a DLBLU. The effect of the rays reflected by the sides of the backlight box was also considered and calculated using the LSF. When comparing the results calculated using the LSF method at $y\; = \;x$ and $y\; = \;0$ with the results from the optical design software, the mean absolute percentage error (MAPE) were 0.74% and 0.46%, respectively. To demonstrate the effectiveness of the LSF method, a DLBLU model with 36 batwing sources was designed using the LSF method and assembled. The measurement result for DLBLU uniformity was 96.68%. When comparing the measurement result with the results of the LSF method at $y\; = \;x$ and $y\; = \;0$ , the MAPEs were 0.92% and 0.46%, respectively. Thus, the proposed design method is an effective method for designing a DLBLU.