The resistive ballast also allows operation on DC supplies such as in trams, trains, etc. I have a commercially made fitting using a 20W TLS tube but is AC only since it contains a conventional iron cored choke ballast. Bear in mind the waveform distortion, so the current/voltage measurements might not be exact, as read by meters calibrated for a sine wave. In practice, they would be close enough however.
The resistive ballast also allows operation on DC supplies such as in trams, trains, etc. I have a commercially made fitting using a 20W TLS tube but is AC only since it contains a conventional iron cored choke ballast. Bear in mind the waveform distortion, so the current/voltage measurements might not be exact, as read by meters calibrated for a sine wave. In practice, they would be close enough however.