The goal was to identify and optimize the common cause factors affecting the service life of krypton-filled vehicle brake bulbs (type 3157K). Also, a reason for vehicle-line to vehicle-line differences in bulb warranty cost was desired. A shaker-table test was developed to allow accelerated evaluation of common-cause factors thought to affect bulb life. Two significant causal design factors were found, 1) filament orientation and 2) centering of main filament coil (between the lead wires). It was concluded that voltage, while having an effect on bulb life, is a noise factor. Optimization of the design factors studied more than doubled observed bulb life.
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