By Randall Elgin, Senior Engineer Lightspan Application Lab, Bill Riegler, Product Director-Engineering Materials, Rob Thomaier, Research Director, NuSil Technology LLC, Carpinteria, CA 93013. Presented at IMAPS Advanced Technology Workshop on Packaging & Assembly of Power LEDs, Palo Alto, CA October 25-28, 2005. Summary This study evaluates twenty-one samples for their change in optical transmission due to a 680-6800J/cm2 dose of UV radiation. Samples were made from UV curing acrylate, epoxy and silicone chemistries. All samples were prepared and exposed the same way so that comparisons between the samples would be meaningful. Given the same dosage of UV, silicones perform better than UV curing acrylates, which perform better than epoxies. Among the silicone samples were those designed to test the following suspected sources for yellowing: 1) Amount of Pt catalyst
2) Amount of Phenyl – related to the refractive index
3) Impurities The results conflict with previous test results, and possible reasons for this are discussed in the report. However, the results show that yellowing is not caused by the amount of platinum, amount of phenyl, nor impurities. View entire whitepaper | 
