Some low-voltage lighting devices suspend the halogen bulbs on wire arms between two non-insulated cables under tension. The cables, as well as providing a mount and supporting the weight of the lamps, carry current, and the potential difference between the cables provides the necessary electricity
for the illumination (i.e. one cable is positive and the other zero volts).
Like most lighting systems, the lamps themselves have a limited life-time and must be periodically replaced. Occasionally replacing a bulb is not usually much of a problem, but as low-voltage lighting usually tends to use a larger number of bulbs, the mean time to failure is greatly increased.
Cable-car lighting uses a simple electrical motor at one wall to drive two pulley wheels, over which two separate loops of cable are passed. Pulleys fastened at the opposing wall complete the loop and provide the necessary tension to keep it taught. The two loops replace the two individual wires in a conventional low-voltage lighting system; the bulbs are hung on wire hooks rather than clamped to the cables. The tension of the loop of wire ensures adequate friction with the motor driven wheel and a suitable wheel surface can be used, such as rubber, to prevent slippage.
An electronic bulb dispenser is mounted above the wires at one end of the contraption and a bulb bin at the other. Bulbs finding their way to their destination pulley will fall from as the cable wraps around the pulley and land in the bulb bin for collection. The speed of the cable feed is set so that a bulbs journey from one end to the other is exactly the estimated life-time of the bulb. The dispenser is set to dispense fresh bulbs at a suitable rate so that the desired number of bulbs is evenly spaced along the cable. Switching off the lights will also power down the motor and dispenser to prevent bulbs being consumed when the system is not being used.
Obviously, with all the extra complexity, such a device would be aimed at organisations rather than home use. For a new installation, the system would be supplied with specially marked bulbs. As these primer bulbs would not complete the entire journey along the cable, they can be saved.