Visit http://www.hubbell.com/ to determine what those Hubbell numbers mean.

I think GE calls their Metal Halide lamps "MultiVapor" which could account for the MVR in the catalog number, the 400 is the wattage & the "U" is for universal position.

If you can lay your hands on a Lithonia catalog, they have a troubleshooting guide in the back.. Or, go to http://www.advancetransformer.com/ and download their "Pocket Guide to High Intensity Discharge Lamps and Ballasts" which also includes a troubleshooting section.

Tom

Few things are harder to put up with than the annoyance of a good example.