The technology of exterior automotive lighting is undergoing the first major change in a half-century. Manufacturers of road vehicles, including motorcycles, are increasingly using Light Emitting Diode (LED) lamps in the place of incandescent light bulbs in exterior lighting applications, including brake lamps, turn signals and parking lamps.
Analysis of incandescent bulb filaments has been well documented (References 2, 3, 4, 5, 6 and 7), and is a well-accepted practice in accident analysis. But little appears to be known about how, or even if, LED lamps respond to the forces of acceleration or direct-impact events to provide a “record” of the state of the lamp at the moment of an accident event. This project examined the responses of lighted and unlighted LEDs to both acceleration and direct impact events for indications of their state of operation when damaged.
The structures of LED bulbs were examined before they were subjected to controlled acceleration and impact events, and those baseline features were compared to the bulbs following testing. LED lamp arrays were tested in the powered (On) and non-powered (Off) states, in order to look for features analogous to the hot-shock and cold-shock characteristics seen in incandescent lamps. Powered and non-powered incandescent lamps were tested alongside the LEDs, to provide a known basis for comparison.
Accelerations from 230 to 700g caused typical hot-shock damage to the filaments of incandescent bulbs, but produced no readily observable changes in the test LEDs. Direct impact damage did cause some LED bulbs to malfunction, but even then, no clear-cut features were found to indicate whether the LED had been on or off when damaged.