lygo-, lyg- +

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

lygomania
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.
lygophil
Preferring shade or darkness.
lygophile
1. Thriving in dark or shaded habitats.
2. A morbid preference for dark places.
3. Longing for dark or gloomy places.
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-.