Well enough. With 10,000 lights, they weren't groping around in the dark unless they wanted to. How much measurable light each bulb or fixture put out, I don't know. I've never seen specifications that exact, but it served them.
Just a guess, but I would think the lighting would not be as white and not quite as bright as that portrayed. It seems as if it might have been a bit more on the orange-ish or yellow-ish side with the early incandescent bulbs ? Or possibly they had developed something for the Titanic that produced a whiter light ?
However, I would also think that the dim red glow of the lamps(as the power begins to fail) in the scene where Rose is searching for Jack is fairly accurate.
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 !
Well, yes I know sets have to be lit in certain ways. But sometimes lighting is darker. I guess what I'm asking is was the lighting in specific rooms like the GS and the DS dimmed, like we see in Titanic 1996, not 1997.