Papers by Author: Lun De Liao

Abstract: The paper proposes a novel time based brightness compensation circuit for LED back light modules. The brightness of LED decays while running under constant current driven condition. We have designed a suitable controller to compensate the driving currents to maintain the brightness. The compensation data were calculated from the relative luminous efficiency – time curve provided by the LED manufacturer and were stored in the microprocessor. -The embedded system used the running time of the LED in the back light module as an independent variable for tuning the driving current. The experiment results showed that the brightness of different operating times’ LED arrays can be held almost the same as the new ones.

Abstract: A novel dual-cone-shaped side-emitting lens cap for High Brightness Light Emitting Diodes (HB-LEDs) is proposed for improving brightness and high uniformity of the direct LED backlight Units (BLUs) for large-sized LCD-TVs. Combining the designed lens cap with red, green and blue (RGB) chips on a Metal Core Printed Circuit Board (MCPCB), the LED module with the proposed cap is able to provide a compact white light source with unique features such as instant color variability and lower power usage, etc. The dual-cone-shaped of the proposed lens cap is designed to emit most of the light rays to the sides, only a small portion of light upward along the optical axis of the lens, providing a uniform luminance distribution and the high brightness on the backlight. In addition, a small reflective surface in semi-circular shape is designed and placed upon the proposed LED module about 10mm, the surfaces of which are attached with reflective films to increase the level of light mixing in the larger, global reflector optical box. With the structure of the LED module well designed, the LED backlight Module would be designed for the large-sized LCDTV using the fewer number of LEDs to lead to lower power consumption. The results indeed identify the attributes of the BLU, which make it possible to achieve excellent backlight performance using a direct illumination approach from the light source of “Dual-Cone-Shaped Side- Emitting Lens Cap of LEDs.”

Abstract: This study develops a highly-efficient light-guide plate for edge lighting backlight module that has no optical films. The light guide plate is designed to control the angle of the incident rays to the top surface from light source, to get the highest uniformity of intensity for thin edge lighting backlight system applications. The micro-prisms of pyramidal shape on the top surface can highly-efficient collimate with the light rays. Another micro-prism of v-cut shape on the bottom surface can reflect the incident light into the front direction and mixing the rays in the lightguide plate with the high uniformity. A novel design concept of the v-cut is the regular density varies of the cut in the LGP. The modeling simulation program, employing a Monte Carlo method based on TracePro software, has optimized the shape of the pyramidal micro-prisms on the top surface and the density distribution condition of the v-cut micro-prisms on the bottom surface, also the multiple scattering characteristics. The two types of the micro-prisms at the top and bottom surface can be highly recommended for the uniformity of the brightness via the optimal design process. Future work is warranted on improving the optical efficiency by using light-emitting diodes as a light source. The backlight module will allow us to increase the optical efficiency and to lower the total cost in portable LCD applications. The study confirms that a uniformity of brightness can be achieved without using any optical films, resulting in a high uniformity of 84%.

Abstract: Using TracePro® Monte-Carlo ray-tracing simulations, this paper investigates the improved light extraction efficiency (LEE) obtained by patterning the surface and/or substrate of GaN LEDs with unique three-dimensional micro-cavity patterns. The simulations commence by considering the case of a sapphire-based GaN LED. The effects on the LEE of the micro-cavity dimensions, the absorption coefficient of the active layer, the point source location, and the chip dimensions are systematically examined. Subsequently, the LEE performance of the sapphire-based GaN LED is compared with that of a thin-GaN LED for various surface texturing strategies. In general, the results show that patterning either the surface or the substrate of the LED structure provides an effective improvement in the LEE of both the sapphire-based GaN LED and the thin- GaN LED. For both LED structures, the maximum LEE enhancement is obtained by patterning both the upper surface of the LED and the substrate surface. However, the simulation results indicate that the improvement obtained in the LEE is the result primarily of pattering the upper surface of the LED.