Backlighting Automotive Telltales with LED Indicators

LED technology offers many reliability advantages over incandescent bulbs for the backlighting of automotive telltales. However, up until recently, LED solutions were not practical due to the high cost. In order to get sufficient legend brightness, automotive designers were forced to either use expensive multiple chip LED indicators or expensive metalized reflectors. This paper describes how a single chip LED indicator can be used to illuminate a 15 mm by 15 mm automotive telltale with an inexpensive white molded plastic optical cavity. Using this indicator and cavity, luminous sterances of over 1000 cd/m² are achievable in the center of the legend and luminous sterances of over 400 cd/m₂ are achievable in the corners of the legend. The paper describes a complete telltale solution including this new LED indicator, the reflector design, and optical test results.