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Many LEDs are typically required to source sufficient light for automotive exterior applications. Maintaining even illumination requires the drive current to be well controlled for all the LEDs in an array. This can be challenging in the voltage driven automotive environment when dual level operation is desired, such as for combined stop and tail function. A current source in the form of an LED Driver Module (LDM) can be employed to drive the LED array. However, a passive resistor network may be capable of driving the LED array with a reduction in both cost and complexity when compared to an LDM solution. The advantages and disadvantages of various passive resistor network configurations for dual level operation will be examined.

Traditionally, automotive instrument clusters have been illuminated using incandescent bulbs. Failures of these bulbs are a source of warranty and repair costs. LED lamps can reduce these costs. In addition, LED lamps have a number of other benefits for instrument cluster designs. This paper describes the design of a hybrid instrument cluster using LED lamps for telltale warning lights and bulbs for gauge lighting. This approach provides a very cost effective design since most telltale warning lights can be illuminated with a single LED. This approach eliminates three quarters of the bulbs in a typical design. Previous SAE papers, 870211 and 900474, have also discussed the use of LED lamps for telltale lighting. These papers used very specialized lamps. This paper discusses several industry standard LED lamp packages in both through-hole and SMT package configurations. Lighting measurements have been done at instrument cluster depths of 10 to 41 mm, to cover most applications.

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.

LED technology offers many advantages over incandescent bulbs for automotive telltales, such as higher mechanical shock and vibration resistance. Unfortunately previous LED products had insufficient optical flux for this application. This paper describes a scries of new LED indicator products that provide significantly higher optical flux than previously available indicators. The paper discusses the key factors involved with a typical telltale backlighting design including optical cavity design, selection of light diffusing films, and contrast enhancement filters and then provides benchmark results for a typical telltale design.