Durability Testing Methodologies for Optical Fibers in Distributive Lighting Systems 960493
Optical fibers for distributive lighting systems must exhibit high transparency and accurate color rendition. These properties must also be maintained after extended use. The SAE Distributive Lighting Task Force is defining the mechanical, optical, and chemical durability specifications for exterior applications, the most demanding of which is forward lighting.
We have developed methods to test the stability of plastic optical fibers to heat, to light, and to combinations of heat and light. When plastic optical fibers fail, it is due to a color temperature shift rather than to a loss in transparency. That is, the light that the fiber or light pipe transmits shows a noticeable color change before its intensity is diminished significantly. The goal is to minimize the color temperature shift from the high-intensity discharge (HID) light sources. Our durability test methods monitor these color changes of transmitted light.
We have graphed the data in Arrhenius-type plots to determine the sensitivity of degradation to temperature and to light flux. We have used this methodology to develop an understanding of some of the important design factors in light pipe durability. The Arrhenius-type data allow one to predict performance under the conditions of a particular application or under cycle tests such as those specified by the SAE. Alternatively, if the conditions of a particular application are known, the temperature sensitivity behavior allows one to design an accelerated test that will mimic actual in-use performance.