The chart room was used by the ship's officers and the navigation room was used by the Commander as far as navigation work was concerned. By the way, the chart room shown above actually extended down and included the area where you show that settee.
They would have blockout curtains. I believe Smith told Lightoller at about 9:30 that if needed he would be right inside. Also, Boxhall said he gave Smith the ships position for 7:30 to put on his (Smith's) chart at around 10pm and that he saw Smith prick the position on his chart at that time.