i`ve the same problem with halogens on the job. found that when the power fluctuated the bulbs blew way too fast. have also seen the same thing happen due to power surges due to lighting, trees rubbing power lines(also varies with daytime/nitetime moisture/wind movement/humidity/ect....), even have had one or two bad trasformers do damage. with the recent heat in tx. there have been several brown downs in my local service area. i don`t know if it is the power loss that does the damage or the surge when full power resumes or the inconsistant heating of the elements. not very good at electrical gremlins, but this type of problem has really cost me time and money in the past. hop this helps.