Philips TL-S bulbs

I think those tubes needed special switches to reverse the polarity each time they were switched on. This was to prevent darkening of one end of the tube after a few hours, caused by migration of the mercury. You may have to replace the switchgear if you fit inverter-powered lamps.

If you contact a tramcar manufacturer, they should be able to put you in touch with some companies that supply modern lighting equipment for 600 VDC.

You might be correct about this in terms of a good practice, but in the design I'm dealing with this is not the case, and thus possibly the reason so many of the tubes burned out. I am in contact with several companies that supply low voltage LED lighting for rail vehicles as a parallel path.

Are you sure they have, in fact, burnt out? If they have gone black at one end, that is most likely because of the mercury migration problem. Reversing the polarity should restore them for a short while until the mercury migrates the other way.

There is a lot of information about this in the Philips Technical Review, I remember reading it but can't remember the date (it might have been in the 1930s).

That's actually a good point. I don't think the maintenance people tried that. I'll go and check if they still have the bad bulbs. Thanks.