When is an auxiliary rear lighting bar (Lichtleiste / Beleuchtungsbalken) legally mandatory on a rear-mounted agricultural implement?

1. Whenever the mounted implement or load hides the tractor's own rear lights, brake lights, indicators, reflectors or number plate
2. Only for journeys made in darkness or poor visibility
3. Only where the implement projects more than 1.00 m beyond the rear of the tractor
4. Never, because a mounted implement is treated as part of the tractor