I think it was the Electronics International [or similar] magazine that published a circuit for a little "dimmer" device for individual bulbs. It was designed to take out 20v or so without affecting the colour temperature or brightness that much but considerably extending the working life of the bulb.
I thought about something similar to reduce the overall voltage of the 5amp lighting circuit for ALL bulbs but never I never got very far with it so I still don't know if it might have worked
Too late now I suppose
Dave W