NJ Wireman and E 57
Have seen that too, on fault finding that the lamp was too close to the lightcell, hence 24 hr lights.
Black tape left on. Done it once myself. While checking a SL cct i was called out to a substaion fault and forget about the black tape. 2 weeks later ??
If the cells are reversed wired load side to line side the lights come on , go off for 4 minutes and go back on and so on.
The one we use here have a bimetallic strip and a heater resistor in them.