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The objective of this study is to design a novel cone-shaped lens cap on LEDs in order to achieve high optical efficiency in an ultra-thin directly lit RGB LED backlight unit (BLU) for large-sized LCD TVs. The use of the novel lens cap could play the role of a diffuser, a low light-efficiency component in a BLU, in order to gain higher efficiency and simultaneously provide satisfactory uniformity in light distribution. The novel cone-shaped lens is coated with aluminum on the outside surface of the cone for mirroring effects to reflect most of the LED emitted light horizontally and then reflect the light at the BLU boundaries, and then, finally to the output plane. In this way, bright spots on the output plane of the BLU can be avoided, leading to increased uniformity. Simulations were conducted to design and optimize varied aspects of the designed lens and BLU, including the cone angle of the proposed lens and the LED spacing (pitch). To further achieve color balance, a known Genetic Algorithm is used to search for the optimal angular placement of each RGB LED, resulting in better color balance. Finally, a prototype BLU for large-sized 37-in. LCD TVs with the proposed lens was built to verify the expected performance. FIGURE 1 -Illustration of directly lit LED backlight units: (a) An ordinary LED BLU; (b) a BLU with the proposed novel cone-shaped LED lenses. Journal of the SID 16/2, 2008FIGURE 7 -Measured intensity profiles for three different novel cone-shaped lenses.FIGURE 8 -The TracePro ray-tracing model for the BLU.FIGURE 9 -Spectrum reflectances of the coated and white reflectors. Journal of the SID 16/2, 2008

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