Gloom is a depressing darkness.

People describe light conditions as gloomy when the rods

Rod cell

Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...

 in their eyes take over from the cones

Cone cell

Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...

 and so their vision becomes shades of grey as they lose their colour vision. Low light of this sort is associated with depression

Depression (mood)

Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...

. This association was made as far back as the 2nd century by the ancient Greek physician, Aretaeus of Cappadocia

Aretaeus of Cappadocia

Aretaeus , is one of the most celebrated of the ancient Greek physicians, of whose life, however, few particulars are known. There is some uncertainty regarding both his age and country, but it seems probable that he practised in the 1st century CE, during the reign of Nero or Vespasian...

, who said, "Lethargies are to be laid in the light and exposed to the rays of the sun, for the disease is gloom."

The naturally weak daylight

Daylight

Daylight or the light of day is the combination of all direct and indirect sunlight outdoors during the daytime. This includes direct sunlight, diffuse sky radiation, and both of these reflected from the Earth and terrestrial objects. Sunlight scattered or reflected from objects in outer space is...

 during winter at extreme latitudes causes winter depression

Seasonal affective disorder

Seasonal affective disorder , also known as winter depression, winter blues, summer depression, summer blues, or seasonal depression, is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms in the winter or summer, spring or autumn...

. Also, weaker electrical activity is found in the retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

s of depressed people, which gives them poor visual contrast

Contrast (vision)

Contrast is the difference in visual properties that makes an object distinguishable from other objects and the background. In visual perception of the real world, contrast is determined by the difference in the color and brightness of the object and other objects within the same field of view...

 so that they see the world in grey, depressing hues. A solarium

Solarium

Solarium may refer to:* Similar to a Sunroom, a room built largely of glass to afford exposure to the sun. Solariums have glass roofs , unlike sunrooms...

 or other source of bright light may be used as light therapy

Light therapy

Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, usually controlled with various devices...

 to treat this.

Where artificial lighting is used, this has to be sufficient to not only illuminate the task area, but also provide sufficient background lighting to avoid a sensation of gloominess which has a negative effect on efficiency. If the task is challenging, such as playing cricket

Cricket

Cricket is a bat-and-ball game played between two teams of 11 players on an oval-shaped field, at the centre of which is a rectangular 22-yard long pitch. One team bats, trying to score as many runs as possible while the other team bowls and fields, trying to dismiss the batsmen and thus limit the...

, then reaction times are found to increase significantly when the illumination declines to the gloom level. This is the level at which car drivers turn their lights

Headlamp

A headlamp is a lamp, usually attached to the front of a vehicle such as a car or a motorcycle, with the purpose of illuminating the road ahead during periods of low visibility, such as darkness or precipitation. Headlamp performance has steadily improved throughout the automobile age, spurred by...

 on.

Gloomy conditions may arise when low cloud cover forms a continuous overcast

Overcast

Overcast or overcast weather, as defined by the World Meteorological Organization, is the meteorological condition of clouds obscuring all of the sky. Overcast, written as "OVC" in the METAR observation, is reported when the cloud cover is observed to equal eight oktas .Sometimes clouds can be...

. This occurs annually in California where it is known as the June gloom

June Gloom

June Gloom is a southern California term for a weather pattern that results in cloudy, overcast skies with cool temperatures during the late spring and early summer. June Gloom in southern California is caused by the marine layer effect common to the West Coast, and is enhanced by the Catalina eddy...

.

In the arts, a gloomy landscape or setting may be used to illustrate themes such as melancholy or poverty

Poverty

Poverty is the lack of a certain amount of material possessions or money. Absolute poverty or destitution is inability to afford basic human needs, which commonly includes clean and fresh water, nutrition, health care, education, clothing and shelter. About 1.7 billion people are estimated to live...

. Horace Walpole coined the term gloomth to describe the ambience of great ancient buildings which he recreated in the Gothic revival

Gothic Revival architecture

The Gothic Revival is an architectural movement that began in the 1740s in England...

 of his house, Strawberry Hill

Strawberry Hill House

Strawberry Hill is the Gothic Revival villa of Horace Walpole which he built in the second half of the 18th century in what is now an affluent area of the London Borough of Richmond upon Thames in Twickenham, London...

, and novel, The Castle of Otranto

The Castle of Otranto

The Castle of Otranto is a 1764 novel by Horace Walpole. It is generally regarded as the first gothic novel, initiating a literary genre which would become extremely popular in the later 18th century and early 19th century...

. Characters which exemplify a gloomy outlook include Eeyore

Eeyore

Eeyore is a character in the Winnie-the-Pooh books by A. A. Milne. He is generally characterized as a pessimistic, gloomy, depressed, anhedonic, old grey stuffed donkey who is a friend of the title character, Winnie-the-Pooh....

, Marvin

Marvin the Paranoid Android

Marvin, the Paranoid Android, is a fictional character in The Hitchhiker's Guide to the Galaxy series by Douglas Adams. Marvin is the ship's robot aboard the starship Heart of Gold...

 and Old Man Gloom

Zozobra

Zozobra is the name of a giant marionette effigy which is built and burned every autumn during Fiestas de Santa Fe in Santa Fe, New Mexico, usually during the second week of September. As his name suggests, he embodies gloom; by burning him, people destroy the worries and troubles of the previous...

.  The catchphrase "doom and gloom", which is commonly used to express extreme pessimism

Pessimism

Pessimism, from the Latin word pessimus , is a state of mind in which one perceives life negatively. Value judgments may vary dramatically between individuals, even when judgments of fact are undisputed. The most common example of this phenomenon is the "Is the glass half empty or half full?"...

, was popularised by the movie Finian's Rainbow

Finian's Rainbow (film)

Finian's Rainbow is a 1968 American musical film directed by Francis Ford Coppola that stars Fred Astaire and Petula Clark. The screenplay by E. Y. Harburg and Fred Saidy is based on their 1947 stage musical of the same name.-Plot:...

in which the leprechaun

Leprechaun

A leprechaun is a type of fairy in Irish folklore, usually taking the form of an old man, clad in a red or green coat, who enjoys partaking in mischief. Like other fairy creatures, leprechauns have been linked to the Tuatha Dé Danann of Irish mythology...

 Og (Tommy Steele

Tommy Steele

Tommy Steele OBE , is an English entertainer. Steele is widely regarded as Britain's first teen idol and rock and roll star.-Singer:...

) uses it repeatedly.