46 C.F.R. § 129.440 – Emergency lighting.

(a) A vessel of less than 100 gross tons must have adequate emergency lighting fitted along the line of escape to the main deck from accommodations and working (machinery) spaces below the main deck.
(b) The emergency lighting required by paragraph (a) of this section must automatically actuate upon failure of the main lighting. Unless a vessel is equipped with a single source of power for emergency lighting, it must have individual battery-powered lighting that is—
1. (1) Automatically actuated upon loss of normal power;
2. (2) Not readily portable;
3. (3) Connected to an automatic battery-charger; and
4. (4) Of enough capacity for 6 hours of continuous operation.