Gloom is a low level of light which is so dim that there are physiological and psychological effects. Human vision at this level becomesmonochrome and has lessened clarity.

Light conditions may be considered gloomy when the level of light in an environment is too low for theproper function ofcone cells, andcolour vision is lost.^[1] In a study by Rothwell and Campbell, light levels described as "gloomy" fell between 28 and 3.6 cd/m².^[2]

Low light and lack of color of this sort may be associated withdepression andlethargy. This association was made as far back as the 2nd century by the ancient Greek physician,Aretaeus of Cappadocia, who said, "Lethargics are to be laid in the light and exposed to the rays of the sun, for the disease is gloom."^[3] Also, some studies have found weaker electrical activity in theretinas of depressed people, which gave the individuals studied poorvisual contrast, meaning that they saw the world in grayer hues.^[4][5] The naturally weakdaylight during winter at extreme latitudes can causeseasonal affective disorder (SAD), although a percentage of people experience SAD during summer.^[6][7] Asolarium or other source of bright light may be used aslight therapy to treat winter SAD.^[3]

Whereartificial 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.^[8][9][10] If the task is challenging, such as playingcricket,reaction times are found to increase significantly when the illumination declines to thegloom level.^[11]

In architecture, the level of lighting affects whether a building is considered to be unappealing. If there is little or no sunlight or view of the outdoor surroundings from within, then this will tend to make the building seem "gloomy". As seen from the exterior, an interior which is brighter than the surrounding light level may cause the overall building to seem gloomy because the normal cues and contrasts have been upset.^[12]

In the arts, a gloomy landscape or setting may be used to illustrate themes such asmelancholy orpoverty.^[13]Horace Walpole coined the termgloomth to describe the ambiance of great ancient buildings which he recreated in theGothic revival of his house,Strawberry Hill, and novel,The Castle of Otranto.^[14] Characters which exemplify a gloomy outlook includeEeyore,Marvin andOld Man Gloom.^[15][16][17] The catchphrase "doom and gloom", which is commonly used to express extremepessimism, was popularised by the movieFinian's Rainbow in which theleprechaun Og (Tommy Steele) uses it repeatedly.^[18]

Gloomy conditions may arise when lowcloud cover forms a continuousovercast. This occurs annually inSouthern California, where it is known asJune Gloom.Anticyclones may generate gloom-like conditions if they remain stationary, causing ahaze and layer ofstratocumulus clouds. These tend to occur intemperate winter at themiddle latitudes or over an extended period insubtropical regions.^[19][20]

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