Grab, here's your answer:

The Flag Code states it is the universal custom to display the flag only from sunrise to sunset on buildings and on stationary flag staffs in the open. However, when a patriotic effect is desired, the flag may be displayed twenty-four hours a day if properly illuminated during the hours of darkness. (ref: Flag Code 6(a)) The American Legion interprets "proper illumination" as a light specifically placed to illuminate the flag (preferred) or having a light source sufficient to illuminate the flag so it is recognizable as such by the casual observer.

The U.S. Government typically flies the flag during daylight, with the general exception of memorials. There they are flown 24 day & night.

Go here for the complete U.S. Flag Code in .doc or .pdf form:

American Legion Flag Code


One of the most interesting parts of the code is the proper disposal of a flag - you burn it.

pax yall