lygo-, lyg- +

(Greek: shadow, shadowy; shade, darkness; twilight; gloomy)

An obsessive desire to be in dark or gloomy places. Many agoraphobics feel more comfortable in the dark than they do when it is light and they can be seen by others.
Preferring shade or darkness.
lygophile (s) (noun), lygophiles (pl)
1. A preference for thriving in dark or shady places: Some plants can be lygophiles and prefer dwelling in dark habitats, like the prayer plant (Maranta leuconeura) or the peace lily (Spathiphyllum cochlearispathum).
2. A person who prefers dark or gloomy places: Celia liked the time of twilight and darkness, so she pulled the curtains to make it quite dim, and perhaps a bit melancholic , in her room And, as a lygophile, she word dark clothes and dyed her hair black!
lygophobia (s) (noun) (no plural)
A loathing of darkness or of gloomy and shadowy situations: Lygophobia describes the fear of blackness, dimness, or of murkiness and is associated with feelings of uncertainty, helplessness, and the inability to see what one is doing, as well as a sense of unfamiliarity because things appear to be different in the dark.

Other related "dark; shadow, shade; black" units: melan-; nigri-; nocti-; nycti-; scoto-; skio-; umbra-.