NavList:

§ 91.209 Aircraft lights.

No person may:

(a) During the period from sunset to sunrise (or, in Alaska, during the period a prominent unlighted object cannot be seen from a distance of 3 statute miles or the sun is more than 6 degrees below the horizon)—

(1) Operate an aircraft unless it has lighted position lights;

(b) Night takeoff and landing experience.

(1) Except as provided in paragraph (e) of this section, no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and—

So it breaks down to --"night" for the purpose of turning on required position lights is sunset.

-------------for logging "night time" flight time experience is the FAR 1 definition, the end of civil twilight, which is approximately 30 minutes after sunset in most of the U.S.

-------------for carrying passengers in the dark, one hour after sunset.

Gary LaPook CFI AI&M 2063232