You have a power plant capable of generating the energy needed to take you to relativistic speeds (at minimum) or punch holes through spacetime (a couple hundred orders of magnitude more) that’ll radiate a Hiroshima per second in waste heat (at 99.99999% efficiency converting energy into movement). You can certainly power a couple light bulbs.
Yeah but you save a couple bucks per ship if you cut the lighting to the absolute minimum required to keep crew shrinkage at an acceptable rate, and across the entire fleet that adds up to a nice bonus.