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Daylight

From Wikipedia, the free encyclopedia
Natural light during the daytime
For other uses, seeDaylight (disambiguation).
World map showing the areas of Earth receiving daylight around 13:00 UTC in April

Daylight is the combination of all direct and indirectsunlight during thedaytime. This includes directsunlight,diffuse sky radiation, and (often) both of these reflected byEarth and terrestrial objects, likelandforms and buildings. Sunlightscattered or reflected byastronomical objects is generally not considered daylight. Therefore, daylight excludesmoonlight, despite it being reflected indirect sunlight.

Definition

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Daylight is present at a particular location, to some degree, whenever theSun is above the localhorizon. This is true for slightly more than 50% of theEarth at any given time, since the Earth's atmosphere refracts some sunlight even when the Sun is below the horizon.

Outdoorilluminance varies from 120,000lux for directsunlight atnoon, which may cause eyepain, to less than 5lux for thick stormclouds with the Sun at the horizon (even <1 lux for the most extreme case), which may make shadows from distantstreet lights visible. It may be darker under unusual circumstances like asolar eclipse or very high levels of atmosphericparticulates, which include smoke (seeNew England's Dark Day), dust,[1] and volcanic ash.[2]

Intensity in different conditions

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IlluminanceExample
120,000 luxBrightestsunlight
111,000 luxBright sunlight
109,880 luxAM 1.5 global solar spectrum sunlight (= 1,000.4 W/m2)[3][circular reference]
20,000 luxShade illuminated by entire clearblue sky, midday
1,000–2,000 luxTypicalovercast day, midday
400 luxSunrise orsunset on a clear day (ambient illumination)
<200 luxExtreme of thickest storm clouds, midday
40 luxFully overcast, sunset/sunrise
<1 luxExtreme of thickest storm clouds, sunset/rise

For comparison, nighttime illuminance levels are:

IlluminanceExample
<1 luxMoonlight,[4] clearnight sky
0.25 luxAfull Moon, clear night sky[5][6]
0.01 luxAquarter Moon, clear night sky
0.002 luxStarlight, clear moonless night sky, includingairglow[5]
0.0002 luxStarlight, clear moonless night sky, excluding airglow[5]
0.00014 luxVenus at brightest,[5] clear night sky
0.0001 luxStarlight, overcast moonless night sky[5]

For a table of approximate daylight intensity in theSolar System, seesunlight.

See also

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References

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  1. ^Cox, Clifford."Dust Bowl".Perryton.com. Retrieved2017-08-01.
  2. ^"Volcanic Ash Impacts & Mitigation".USGS. Retrieved2017-08-01.
  3. ^"Air mass (solar energy)". Wikipedia. Retrieved14 April 2020.
  4. ^Bunning, Erwin; Moser, Ilse (April 1969)."Interference of moonlight with the photoperiodic measurement of time by plants, and their adaptive reaction".Proceedings of the National Academy of Sciences of the United States of America.62 (4):1018–22.Bibcode:1969PNAS...62.1018B.doi:10.1073/pnas.62.4.1018.PMC 223607.PMID 16591742.
  5. ^abcdeSchlyter, Paul (2006)."Radiometry and photometry in astronomy FAQ".
  6. ^"Petzl reference system for lighting performance". Archived fromthe original on 2008-06-20. Retrieved2007-04-24.

External links

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Parts of aday
Daytime
Twilight
Night
Related
Authority control databases: NationalEdit this at Wikidata
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