Menu
Home Explore People Places Arts History Plants & Animals Science Life & Culture Technology
On this page
Daylight
Combination of all direct and indirect sunlight outdoors during the daytime

Daylight is the combination of all direct and indirect sunlight during the daytime. This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunlight scattered or reflected by astronomical objects is generally not considered daylight. Therefore, daylight excludes moonlight, despite it being reflected indirect sunlight.

Related Image Collections Add Image
Profiles
1 Image
We don't have any YouTube videos related to Daylight yet.
We don't have any PDF documents related to Daylight yet.
We don't have any Books related to Daylight yet.
We don't have any archived web articles related to Daylight yet.

Definition

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

Outdoor illuminance varies from 120,000 lux for direct sunlight at noon, which may cause eye pain, to less than 5 lux for thick storm clouds with the Sun at the horizon (even <1 lux for the most extreme case), which may make shadows from distant street lights visible. It may be darker under unusual circumstances like a solar eclipse or very high levels of atmospheric particulates, which include smoke (see New England's Dark Day), dust,1 and volcanic ash.2

Intensity in different conditions

IlluminanceExample
120,000 luxBrightest sunlight
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 clear blue sky, midday
1,000–2,000 luxTypical overcast day, midday
400 luxSunrise or sunset 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 clear night sky
0.25 luxA full Moon, clear night sky56
0.01 luxA quarter Moon, clear night sky
0.002 luxStarlight, clear moonless night sky, including airglow7
0.0002 luxStarlight, clear moonless night sky, excluding airglow8
0.00014 luxVenus at brightest,9 clear night sky
0.0001 luxStarlight, overcast moonless night sky10

For a table of approximate daylight intensity in the Solar System, see sunlight.

See also

References

  1. Cox, Clifford. "Dust Bowl". Perryton.com. Retrieved 2017-08-01. http://www.perryton.com/black.htm ↩

  2. "Volcanic Ash Impacts & Mitigation". USGS. Retrieved 2017-08-01. https://volcanoes.usgs.gov/ash/ ↩

  3. "Air mass (solar energy)". Wikipedia. Retrieved 14 April 2020. https://en.wikipedia.org/w/index.php?title=Air_mass_(solar_energy)&oldid=938950059 ↩

  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. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC223607 ↩

  5. Schlyter, Paul (2006). "Radiometry and photometry in astronomy FAQ". http://stjarnhimlen.se/comp/radfaq.html#10 ↩

  6. "Petzl reference system for lighting performance". Archived from the original on 2008-06-20. Retrieved 2007-04-24. https://web.archive.org/web/20080620123040/http://en.petzl.com/petzl/frontoffice/Lampes/static/referentiel/present_referentiel_en.jsp ↩

  7. Schlyter, Paul (2006). "Radiometry and photometry in astronomy FAQ". http://stjarnhimlen.se/comp/radfaq.html#10 ↩

  8. Schlyter, Paul (2006). "Radiometry and photometry in astronomy FAQ". http://stjarnhimlen.se/comp/radfaq.html#10 ↩

  9. Schlyter, Paul (2006). "Radiometry and photometry in astronomy FAQ". http://stjarnhimlen.se/comp/radfaq.html#10 ↩

  10. Schlyter, Paul (2006). "Radiometry and photometry in astronomy FAQ". http://stjarnhimlen.se/comp/radfaq.html#10 ↩