I seen an electrician get a bang like this with a 2x PL 18W fixture

He installed the new fixture, flipped the switch, BANG bright flash tripped breaker

Reset the breaker, fixture flashing without coming on steady

Opened the fixture with the power on to look inside

The fixture was wired incorrectly from the factory - When power connected to the terminal block, 1 PL was directly across the mains and 1 with 2 ballasts in series

Now the REALLY weird part : The PL that banged with diret connection to mains, did light dimly and unstable (like cold cathode discharge) IN THE PL TUBE when connected to the mains again without ballast, though when shaked you could hear something rattling inside - probably the starter glow bottle loose after its wires fused, or it just exploded. If the PL tube did have small discharge without any ballast in series with it, how this discharge sustained without going bang again ? O_o

The other PL on 2 ballasts in series was just flashing as the lamp was not keping on or the starter was not going off after striking

The electron emission was limited by the saturated emission of the cold makeshift electrode (from remains of the electrode assembly). As the discharge was too weak, it did not heat it up.

The same discharge happen in many tubes without starter - you have very small current, so nearly o voltage drop across the ballast, so for the small current technically the same situation as direct connection to the mains.
But this state is heavily unstable - the electrode may form a hot spot (when there is no ballasting impedance => BANG) or the discharge cease (= darkness), so that is why this operating mode is practically unusable.

@ Powell, does your desk lamp have was paper capacitors wired across the "starter" switch?  I have one that the tube glowed continuously like you mentioned and the trouble was a shorted wax paper cap.  I cut it out and it works fine now.  Mine is a two tube fixture, with two choke ballasts and two "push, hold, release" switches.

No. In fact I have never seen that. If I DID, I would replace the paper capacitor with a ceramic one.

Off topic, but what guests viewing this? Man bots are weird here.