Helmet-Mounted Display Sighting System (HMDSS) for advanced rotorcraft requires an extra high luminance backlight to provide the needed display contrast ratio under high ambient lighting conditions. Light Emitting Diode (LED) is selected as the source of illumination because of its high efficiency, compactness, high reliability, and high luminous intensity. This paper describes typical designs of high efficiency and high luminance LED backlight that meets these requirements. Design issues such as light collection efficiency, spatial and angular uniformity, power consumption, color shift, and other optical performance of the backlight will be addressed. With proper selection of LED and adequate optical design, more than 30,000 fl. using only 1.5 watts electrical power is achieved.