Gloom

Gloom is a low level of light which is so dim that there are physiological and psychological effects. Human vision at this level becomes monochrome and has lessened clarity, making any environment more unpleasant to be in.

Light conditions are considered to be gloomy when the level of light in an environment is too low for the proper function of cone cells occurs, and colour vision is lost^[1] In a study by Rothwell and Campbell, light levels described as "gloomy" fell between 28 and 3.6 cd/m^-2. 

Low light and lack of color of this sort is associated with depression and lethargy. 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.". Also, weaker electrical activity is found in the retinas of depressed people, which gives them poor visual contrast so that they see the world in gray, depressing hues. The naturally weak daylight during winter at extreme latitudes causes Seasonal affective disorder. A or other source of bright light may be used as light therapy to treat such a condition.

Where artificial lighting is used, this has to be sufficient enough 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, reaction times are found to increase significantly when the illumination declines to the gloom level.

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.

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