As in any movie the scenes have to be carefully "lit" by experts in this field to enhance the background for the actors/actresses and to show the actors/actresses themselves. Most, if not all, of the interior scenes in "Titanic" are much more evenly "lit" than they would have been in reality. The work of the lighting engineers in movies seems to be an art in itself.
Possibly the only scenes in "Titanic" that are realistically lighted are the day scenes on deck...such as where Jack first sights Rose...the infamous "spitting" and "King of the World" scenes... and others filmed in natural daylight.
The final sinking scene (Jack and Rose clinging to the railing, etc.) would have been pitch dark...the only light would have been dim starlight.
Passengers in the life boats reported they were unable to see anything when the lights went out since their eyes had not had time to adjust for the darkness. But movies have to have some lighting to show the action and the show must go on !
