Byung-Yun Joo

Design guidance of backlight optic for improvement of the brightness in the conventional edge-lit LCD backlight

Abstract An edge-lit backlight as a surface illuminator in the liquid crystal display achieves high brightness illumination with the light-condensing optic, composed of lamps, a light guide plate, a reflection film, a diffuse film, and a brightness enhancement film (BEF). This paper dealt with a technique to improve the brightness of a LCD backlight by increasing the light-condensing efficiency of an existing BEF. First, the technique was proposed; the efficiency of a BEF can be improved by a proper shaping of the angular luminance of lights entering the BEF. Then, its validness was experimentally proved with investigation of the brightness change of a test monitor backlight, varying the angular shape of the incident light to a BEF by adjusting the scattering power of both a diffuse film and an ink material printed on a light guide plate. It was revealed that the improvement range of the brightness by the proposed technique is about 5–9%.

Analysis of Color Uniformity of White LED Lens Packages for Direct-lit LCD Backlight Applications

Recently, the color separation issue of wide-spreading white LEDs has attracted attention due to their wide applicability as light sources in direct-lit LCD backlights. These wide-spreading LED packages usually consist of LED chips, a color-conversion phosphor layer, and a light-shaping lens. The technical aspect of this color issue was related to a method for balancing the yellow spectral component emitting from phosphors with respect to the blue one from the LED chip as a function of viewing angle. In this study, we suggested an approach for carrying out quantitative analysis for the color separation problem occurring in wide-spreading LED packages by optical simulation. In addition, the effect of an internal scattering layer on the color uniformity was investigated, which may be considered as a potential solution for this problem.

Optimization of Cutoff Shields in Projection Headlight Systems to Achieve High Intensity Gradient and Low Color Separation at the Cutoff Line

The shape and location of the cutoff shield in a projection-type headlight system were optimized by a ray-tracing technique. A shield based on a Petsval surface showed better cutoff characteristics than a flat or cylindrical shield, such as a sharp intensity gradient and less color separation at the cutoff line. Adjustment of the shield’s location between the reflector and the aspheric lens further improved its cutoff characteristics.

Simulation Study of Injection-Molded Light Guide Plates for Improving Luminance Uniformity Based on the Measured Replication Quality of Micro-Patterns for LED TV Backlight

In the injection-molded light guide plate the replication quality, i.e. the reproduction accuracy, of micro-patterns should be high and uniform over the entire surface area. However technical difficulty in meeting the necessary replication quality arises as the plate size becomes large for TV applications. We propose a simulation technique to optimize the distribution of micro-patterns on a 55-inch injection molded light guide plate considering non-ideal replication quality of micro-patterns. The luminance uniformity could be improved by more than 16% by optimizing the pattern distribution in spite of the same replication quality.

Optimization of Ultrathin Backlight Unit by Using a Tapered Light Guide Film Studied by Optical Simulation

Optical structures of a tapered ultra-thin light guide film (LGF) were optimized by optical simulation for increasing coupling efficiency between light sources and the LGF. A serration pattern on the entrance side surface could provide a comparable coupling efficiency to that of the conventional LGF where a linear, asymmetric prism array was formed on the taper surface. Several micro-patterns were applied to the top and/or bottom surface of the LGF for achieving better luminance property, and it was found that an optimized micro-pyramid pattern exhibited the highest average luminance together with satisfactory luminance uniformity.

Simulation Study on the Minimization of Moiré Patterns Caused by Microlens Array Films for Backlight Applications

Microlens array (MLA) films have been used as brightness-enhancement components in many illumination systems, such as a backlight, which should meet the industrial needs of low cost and high brightness performance. A hexagonally-arranged MLA (HA-MLA) was chosen due to its high filling factor, which was a prerequisite for achieving high brightness-enhancement capability. The moir

Development of a Ray-Tracing Optical Simulation Model of Plasma Display Panel

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Light guide plate and backlight assembly using the same

fringes produced in a film stack composed of two HA-MLA were investigated, under four different lens configurations, by optical simulation. It was found that randomizing the lens configuration, while keeping the filling factor high, was effective way to develop high-gain MLA films for backlight applications.

Micro-hole fabrication by mechanical punching process

A ray-tracing model is developed for accurate optical simulation of plasma display panel (PDP). Thorough spectroscopic characterization of materials properties is carried out, based on which four types of material models of PDP layer materials are developed and incorporated in the cell model. Four test panels with different bus electrode structures are fabricated, the geometrical structure of which is measured and reflected in the ray-tracing model. Plasma fluid simulation is carried out to derive the spatial distribution of the ultraviolet light in the cell and the total number of Xe species. Simulation results show that the simulated panel reflectances are consistent with the experimental values within 3% error. In addition, the normalized angular luminance profiles obtained by simulation agree well with the measured results. However, the on-axis luminance value of the PDP panel, which is affected by both optical and plasma simulation, cannot be predicted accurately by this study.