When driving at night with high-beam headlights (feux de route), when MUST you switch to low-beam headlights (feux de croisement)?

1. As soon as an oncoming vehicle approaches, or when following closely behind another vehicle, to avoid blinding other drivers
2. Only after the oncoming driver flashes their high beams at you three times
3. Only when driving on roads illuminated by street lighting
4. Never, because high beams provide the maximum personal view of the road ahead