Emergency light
The emergency light was a type of light used aboard Federation starships. This light was powered by either auxiliary power or by a battery. When a starship lost main power, these lights were turned on automatically or by manual control. The lights would provide illumination to an otherwise dark ship. 

In 2286, after the Whale Probe disabled the  and deprived it of main power, the captain ordered these lights to be activated. ()
Energy technology