A b o u t

Darkness (also called lightlessness) is the absence of light. A dark area has few, if any, light sources present, making everything hard to see, like at night. Exposure to alternating light and darkness (night and day) has caused several evolutionary adaptations to darkness.
When a vertebrate, like a human, is placed in a dark area, its iris dilates, allowing more light to enter the eye and improving night vision. As a poetic term, darkness can also mean the presence of shadows, evil, or depression.
Darkness can have a strong psychological impact. It can cause depression in people with seasonal affective disorder, fear in nyctophobics, comfort in lygophilics, or attraction as in gothic fashion. These emotions are used to add power to literary imagery.

[ Thanks to Wikipedia ]