nyctophobia

/ˌnɪktəˈfoʊbiə/

If you need your bedroom to be completely dark in order to fall asleep, you definitely don't suffer from nyctophobia. Anyone with this irrational fear is terrified by the darkness of the night.

A phobia is a feeling of extreme anxiety about something that's almost always harmless. Nyctophobia adds the Greek nykti, "night," to phobia, or "fear." Being intensely afraid of the dark at night is very common, especially in children. Even adults sometimes get spooked when the lights go out — especially after watching a scary movie. It's only when that fear becomes overwhelming and persistent that it may be diagnosed as nyctophobia.

Definitions of nyctophobia

1. noun

   a morbid fear of night or darkness
   type of:

   simple phobia

   any phobia (other than agoraphobia) associated with relatively simple well-defined stimuli