Which is a requirement for small unmanned aircraft to be flown at night?

For small unmanned aircraft to be flown at night, it is required that the drone is equipped with special lighting. This lighting must make the aircraft visible for other pilots in the area to observe and avoid during nighttime operations. According to FAA regulations, the lights must have the capability to illuminate the aircraft and be visible for a minimum distance (typically at least 3 statute miles) so that it can be seen by other air traffic. This requirement is crucial for maintaining safety in the airspace during hours of reduced visibility.

While other options may seem relevant, they do not meet the specific regulatory requirements set by the FAA for nighttime operations.