Darkness (also called lightlessness) is the absence of light. Scientifically it is only possible to have a reduced amount of light. The emotional response to an absence of light has inspired metaphor in literature, symbolism in art, and emphasis.

Scientific

However; light cannot simply be absorbed without limit. Energy, like visible light, cannot be created or destroyed. It can only be converted from one type of energy to another. Most objects that absorb visible light reemit it as infrared light. So, although an object may appear dark, it is likely bright at a frequency that a human being cannot see. For more information see thermodynamics.

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.

The scientific definition of light includes the entire electromagnetic spectrum, not just visible light, so it is scientifically impossible to create perfect darkness. For example, all objects radiate heat in the form of infrared light and gamma rays, extremely high frequency light, can penetrate even dense materials.

Poetic

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.

Religious texts often use darkness to make a visual point. In the Bible, darkness was the second to last plague (Exodus 10:21) and the location of “weeping and gnashing of teeth.” (Matthew 8:12) The Qur'an has been interpreted to say that those who transgress the bounds of what is right are doomed to “burning despair and ice-cold darkness.” (Nab 78.25) In Greek Mythology, three layers of night surround Tartarus, a place for the worst sinners as far beneath Hades as heaven is high above earth.

The Hindu goddess Kalí (black, dark colored) is also closely associated with darkness and violence, though she is equally associated with motherhood and benevolence.

In Chinese philosophy Yin is the feminine part of the Taijitu and is represented by a dark lobe.

The use of darkness as a rhetorical device has a long standing tradition. Shakespeare, working in the 16th and 17th centuries, made a character call Satan the “prince of darkness” (King Lear: III, iv) and gave darkness jaws with which to devour love. (A Midsummer Night's Dream: I, i) Chaucer, a 14th century Middle English writer, wrote that knights must cast away the “workes of darkness.” Dante described hell as “solid darkness stain'd.”