### Clue: Floodlights not working? Ground vessel on delta (5-4)
### Answer: PITCH-DARK 
 ### Explanation: Definition: Floodlights not working
 PITCH(the ground on which a sporting game is played) + [ ARK(a vessel, famously built by the Biblical Noah) **placed after**(on) D(letter represented by "delta" in the phonetic alphabet).
Defn: If the floodlights, say, at a sports ground or stadium aren't working, then it would presumably be extremely or totally dark.