I am an electrician who is stumped. I suppose that I could work this out in time but I have never run into a problem like this before. Recently I installed two new T8 ballasts in two separate 48inch T8 fixtures. Replacing the 48 inch T8 tubes I discovered that ony one tube will light at a time. The addition of another tube, completing the fixture's tube complement, results in no hint of a lighting, the first one introduced remaining lit. On the other hand, loosening the first tube results in the second one firing up immediately. Twisting the first tube back into its ceramic fittings results in no light whatsoever! Should I reverse the polarity of the wiring emanating from the ballasts. It seems that reversing the tubes should achieve the same result. I tried that too, but no change in the result. As stated before, this phenomenon is happening in two separate fixtures! The ballasts labeling say that it will fire up two T8 tubes, so what is going on? What has this old man overlooked? This is embarrasing having been in the business since 1959. I've never experienced a situation in florescent lighting that I could not resolve -- there's not THAT MUCH to it! Oh woe! Thank you, Neal