Tubes for 8' 100Watt and 125Watt fittings are no longer manufactured, and the remaining stocks are becoming scarce and expensive. This means that many fully-functional 8' fittings are being disposed-of for the want of a new tube. I realised that the only fundamental differences between these and the shorter variants are the length and, of course, the rating of the choke ballast. Therefore, I took one scrap 8' fluorescent fitting, removed the tube connector from one end, cut two feet from one end of the metal chassis and cover-plate, then re-attached the tube connector. After fitting a 6' tube, I connected it to the 230V A/C mains. Guess what? - It started instantly, and the light output was bright and stable.
I realise that the 75/85W tube is slightly over-run on the 100W ballast, which may reduce its life somewhat, but both tube and choke ran at reassuringly low temperatures, and I shall only know what the long-term reliablity will be in the fullness of time. Nevertheless, this seems like the ideal way to re-use these old fittings, and save significant quantities of cash when one is required for your garage, workshop, or similar locations. It is, of course, essential to ensure that the IP rating of the fitting is maintained, so that no access to live parts is possible once installed. I shall add some photographs and current measurements when I have time.
I believe that 6' tubes will eventually suffer the same fate as 8' tubes. When this happens, I shall try the same trick by cutting-down scrap 6' fittings to fit 5' tubes.
Please note that this is intended as an idea for discussion, and if you decide to try it for yourselves, you are wholly responsible for any and all consequences.