nyctophobia
noun
nyc·to·pho·bia ˌnik-tə-ˈfō-bē-ə 
: abnormal fear of darkness
Example Sentences
Recent Examples on the Web When an extreme version manifests in adulthood, it's known as nyctophobia (from nyx, the Greek word for night), a condition that has afflicted everyone from Augustus Caesar to Keanu Reeves to Muhammad Ali. 
Patrick Blanchfield, Esquire, 1 Aug. 2017
Patrick Blanchfield, Esquire, 1 Aug. 2017 Word History
First Known Use
1882, in the meaning defined above
Medical Definition
nyctophobia
noun
nyc·to·pho·bia -ˈfō-bē-ə
: abnormal fear of darkness