Design of a novel LED lens cap and optimization of LED placement in a large area direct backlight for LCD-TVs

Abstract

A novel cone-shaped 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 area 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 [1] [2]. The cone shape of the proposed lens cap is designed to emit only a small portion of light upward along the optical axis of the lens, while most of the light rays to the sides, providing a uniform luminance distribution and the high brightness on the backlight. In addition, a small, local square reflective box is designed and coupled to enclose the proposed LED module[3] [4] [5], the inner surfaces of which are attached with reflective films to increase the level of light mixing in the larger, global reflector box. With the structure of the LED module well designed, the placement of the LED modules in the BLU is next optimized via the method of optimization algorithm (OA). In the process of OA executions, the locations of the LED modules are the design factors to be optimized with chosen enclosure dimensions and number of LEDs to maximize brightness and uniformity of the entire BLU. Moreover, in the OA process, the software TRACEPRO is utilized to compute brightness and uniformity of the BLU with certain combination of the aforementioned design and control parameters considered. With the theoretically-optimized placement of the LED modules in hand, experiments based on a realistic BLU built in the laboratory are conducted to verify the performance of the proposed LED module and associated optimized locations. 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 "Cone-Shaped Lens Cap of LEDs".