G7PSK, They work on 50Hz, but are brightest at between 400-1kHz, as they are basically a capacitor. Need a pure well filtered sine wave drive, as they are basically a lossy capacitor. Sine wave to reduce the radiated EMI, as they are very effective radiators of harmonics.
T4P, T5 tubes are really bad for loss of emission, and they unfortunately can only be run within a very narrow current band, as this is the only point where they are going to last. Too high and they overheat and dim, too low and they strip cathode fast. Only thing going for them is they use less material to make. T8 tubes I use last up to 10 years on magnetic ballasts, on 5 days a week for 9 hours. Cheap OHJ has a life of between 6 hours to 6 years, all depending on how it was made.