Sonar Room
The sonar room is dominated by sonar consoles. Two modes of sonar observation are used. In the "active" mode, the echoes of sound waves sent out from the sub are timed and analyzed. In the passive mode, instruments listen to the sounds of the surrounding waters.
The room is illuminated by blue light partly to help the technicians easily read the sonar monitors and partly to keep light away from the nearby Control Room. At night, the control room is "rigged for black," in order to maintain the Officer of the Deck's eyes adapted to night vision and to prevent light escaping from the Control Room's periscope, which may be out of the water, giving away the sub's location.
Diagram reprinted from Tom Clancy's Submarine: A Guided Tour Inside a Nuclear Warship, Laura Deninno, Series Illustrator.