The Flag Code of 1923 states that flags should be lowered at sunset but makes exceptions when they can be lit at night. Another special exception was for Fort McHenry. The Battle of Baltimore saw the US flag (storm flag) flying all night and through thunderstorms until the morning reveille when the larger (star spangled banner) was raised. Was it usual to have a flag over a fort (as opposed to a ship) fly at night during battle ? Was any lighting (other than rockets) customary and used ? When did the custom change (if so) in that area / time ?
Hi there -- the most basic answer as to why the flag at Ft. McHenry was not lowered during its bombardment was that the lowering of a flag would have been a signal of surrender. Military etiquette during the War of 1812 was to regard things like fortresses and ships flying a foreign (enemy) flag as belligerent; the lowering of the national flag was a sign of surrender, at which point the other side would be expected to cease firing itself, take possession of the ship or fortress, and offer aid to the wounded. The point of the poem/anthem is that the flag flying in the morning was a sign that the fort had not surrendered overnight.
As to the question about the 1923 flag code, I am not an expert in the area, but have visited Ft. McHenry and understand its "exception" to the general rule to have been made by a postwar (post-WWII) presidential proclamation, due to its historic nature.