What is required for a UAS to be flown legally at night?

For a UAS (Unmanned Aircraft System) to be flown legally at night, it must be equipped with anti-collision lighting systems. This requirement is in place to ensure that the aircraft is visible to other air traffic, including manned aircraft, as well as to the operators of the drone. The lighting helps prevent mid-air collisions and enhances overall flight safety during nighttime operations.

While night vision equipment, FAA headquarters approval, or radar systems may enhance safety or be used under specific conditions, they are not mandatory for all nighttime drone operations according to FAA regulations. The anti-collision lighting requirement is a crucial safety feature for any UAS intending to operate after sunset, making it the correct answer in this context.