**High beam headlights** or **main beam headlights** are used to illuminate a long distance ahead of the vehicle, especially in low-light conditions. These lights are very powerful and white in color, which can dazzle other drivers.

- **Use on interurban roads:**
It is mandatory to turn on the high beam headlights on **roads outside towns or cities** when driving at night and there is little natural light, as long as you are going more than 40 kilometers per hour. They should also be used in tunnels outside a municipality that are not well-lit, regardless of the time of day.

- **Prohibitions:**
These lights should not be used within **towns and cities** because they can dazzle other drivers. Additionally, they should not be on when the vehicle is stationary.

Therefore, the correct answer is that high beam headlights should be turned on in **insufficiently lit interurban roads**.