A novel lens for high-luminance LED direct backlight

Low light utilization rate of about only 5% for LED backlight that needs much more LEDs to ensure the luminance of LED display is rather a challenge, which offers one reason for LED display's high price [1]. In this paper, effect of reflecting property of cavity walls and emergent angle of the light emitting from LED on the transmittance of prism sheets in bottom-lit LED backlight system was investigated. Through simulation, the transmittance varies greatly both in longitudinal and latitudinous direction when light passes through brightness enhancement film (BEF) [2–6]. As emergent angle was demonstrated to have great effect on the transmittance, freeform lens was designed to redistribute the intensity of emitting light to enhance the transmittance. We find that a freeform lens designed according to the transmittance of BEF, the luminance of the backlight can be enhanced as much as two times more than traditional backlight without any lens.