What are the working conditions? Height, obstructions, access during normal hours, disposal of old lamp, ground level office or 35th floor.
What would you charge to engineer this project?
It did how ever make me ask myself was it the lamps or the ballast, was it on dimmer? Well all tomestone wiring is not equal and certain wired arragements will shorten both lamp and ballast, esp. in respects to a dimmer ballast... who knew, well I didn't! (I've doubled up).
Here's a twelve page PDF from one major ballast manufacture on Ballast Life.