need to giggle actinic bulbs

[Delphinus]

What are you using for sockets?

Generally speaking, when I've had this kind of problem, it has been either old bulbs, or sometimes if you're using just the standard white fluorescent sockets, it was because the spacing between them was not "just right" and it required an adjustment so that it was a tighter fit for the bulb.

Or, perhaps it's the sockets themselves, maybe a spot of corrosion or something on the contacts .... maybe check that possibility, either replace the sockets if that's the case, or try sanding the contacts a bit maybe.

Just some ideas to try, HTH...