Daylight 2301573 225674720 2008-07-14T21:06:37Z Mercenario97 4511633 /* External links */ {{otheruses2|Daylight}} [[Image:Daylight.png|thumb|300px|World map showing daylight around 13:00 UTC, April 2nd.]] '''Daylight''' or '''the light of day''' is the combination of all direct and indirect [[sunlight]] outdoors during the [[Daytime (astronomy)|daytime]] (and perhaps [[twilight]]). This includes direct [[sunlight]], [[diffuse sky radiation]], and (often) both of these reflected from the [[Earth]] and terrestrial objects. Sunlight scattered or reflected from objects in outer space (that is, beyond the Earth's atmosphere) is generally not considered daylight. Thus, [[moonlight]] is never considered daylight, despite being "indirect sunlight". ''Daytime'' is the period of time each day when daylight occurs. == Definition == Daylight is present at a particular location, to some degree, whenever the [[sun]] is above the horizon at that location. (This is true for slightly more than 50% of the [[Earth]] at any given time. For an explanation of why it is not exactly half, see the section labeled "introduction" on the [[day]] article). However, the outdoor [[illuminance]] can vary 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 light]]s visible. It may be darker under unusual circumstances such as a [[solar eclipse]] or very high levels of atmospheric smoke. ==Daylight intensity in different conditions== [[Image:Nightfall europe-and-afrika 20050507-184500.jpg|thumb|250px|Artificial image showing a nightfall over Europe and Africa. The solar terminator is shown for UTC July 5, 2005 18.45.00]] {| class="wikitable" !Illuminance!!Example |- |120000 lux||Brightest sunlight |- |110000 lux||Bright sunlight |- |20000 lux||Shade illuminated by entire clear blue sky, midday |- |10000 - 25000 lux||Typical overcast day, midday |- |<200 lux||Extreme of darkest storm clouds, midday |- |400 lux||[[Sunrise]] or [[sunset]] on a clear day (ambient illumination). |- |40 lux||Fully overcast, sunset/sunrise |- |<1 lux||Extreme of darkest storm clouds, sunset/rise |} For comparison, nighttime illuminance levels are: {| class="wikitable" !Illuminance!!Example |- |<1 lux||[[Moonlight]]<ref>{{cite journal |last=Bunning |first=Erwin |coauthors= and Moser, Ilse |year=1969 |month=Apr. |title=Interference of moonlight with the photoperiodic measurement of time by plants, and their adaptive reaction |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=62 |issue=4 |pages=1018–1022 |url=http://www.pnas.org/cgi/reprint/623/4/1018 |doi=10.1073/pnas.62.4.1018 |accessdate=2006-11-10 |pmid=16591742 }}</ref> |- |0.25 lux||Full Moon on a clear night<ref>{{cite web | url=http://en.petzl.com/petzl/frontoffice/Lampes/static/referentiel/present_referentiel_en.jsp |title=Petzl reference system for lighting performance |accessdate=2007-04-24 |format=html }}</ref> |- |0.01 lux||Quarter Moon |- |0.001 lux||Moonless clear night sky |- |0.0001 lux||Moonless overcast night sky |- |0.00005 lux||Starlight |} ==Daylight intensity in the Solar System== {{Merge|sunlight|date=December 2007}} Different bodies of the [[Solar System]] receive light proportionally to the square of their distance from Sun. A rough table comparing the amount of light received by each planet on the Solar System (and the [[dwarf planets]] [[Ceres (dwarf planet)|Ceres]] and [[Pluto]]) follows (from data in [http://www.starhop.com/High/SolInt-19.pdf]): {| class="wikitable" |- ! Planet ! Distance from Sun ([[Astronomical unit|AU]]) ! Relative solar intensity |- | [[Mercury (planet)|Mercury]] | 0.387 | 6.68 |- | [[Venus]] | 0.723 | 1.913 |- | [[Earth]] and [[Moon]] | 1 | 1 |- | [[Mars]] | 1.524 | 0.431 |- | [[Ceres (dwarf planet)|Ceres]] | 2.765 | 0.131 |- | [[Jupiter]] | 5.203 | 0.0369 |- | [[Saturn]] | 9.539 | 0.0110 |- | [[Uranus]] | 19.189 | 0.00272 |- | [[Neptune]] | 30.060 | 0.00111 |- | [[Pluto]] | 39.439 | 0.00064 |} The actual brightness of daylight that would be observed at the surface depends also on the presence and composition of an [[atmosphere]]. For example [[Venus]]' thick atmosphere reflects up to 60% of the solar light it receives, so the actual illumination of the surface is comparable to that of Earth. Daylight on Mars would be more or less like daylight on Earth wearing sunglasses, and as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus it would give perceptions and "feel" very much like Earth daylight. For comparison purposes, daylight on Saturn is somewhat slightly brighter than Earth daylight on the average sunset or sunrise. Even on Pluto the Sun would be still bright enough to almost match the average living room. To see the Sun shine as dim as the full Moon on the Earth, a distance of about 500 AU is needed: there is only a handful of objects in the solar system known to orbit farther than such a distance, among them [[90377 Sedna]] and [[(87269) 2000 OO67]]. == Effects == [[Image:Terminator line January.png|thumb|Daylight in January. Some people choose not to live in polar regions because of the extreme differences in the amount of daylight in summer and winter.]] Daylight is widely accepted to have a positive psychological effect on the human being, and consequently more cases of [[mental health]] problems are registered during the winter months than during the summer months due to the shortened periods of daylight. Cases of [[Clinical depression|depression]] specifically linked to limited daylight are referred to as [[seasonal affective disorder]]. [[Daylighting]] is lighting an indoor space with openings such as [[window]]s and [[wikt:skylight|skylight]]s that allow daylight into the building. This type of lighting is chosen to save [[energy]], to avoid hypothesized adverse health effects of [[over-illumination]] by artificial light, and also for [[aesthetics]]. In recent years, work has taken place to recreate the effects of daylight artificially. This is however expensive in terms of both equipment and energy consumption and is applied almost exclusively in specialist areas such as [[filmmaking]], where light of such intensity is required anyway. ==See also== * [[Rights of Light]] * [[Twilight]] * [[Moonlight]] * [[Daylight saving time]] * [[Daylighting]] ==Notes== <references /> == External links == *[http://www.rics.org/Property/Propertymanagement/Easements/Rightstolightdetermination Royal Institution of Chartered Surveyors - Rights to Light Determination Homepage] *[http://daylightchart.sourceforge.net/ Daylight Chart] shows sunrise and sunset times in a chart, for any location in the world. *[http://www.rgbpixels.ca/daylight_google_map Daylight Google Map and Satellite View] *[http://www.phonebookoftheworld.com/ Daylight Phonebook of the World Map] [[Category:Light]] [[Category:Atmospheric and ocean optics]] [[Category:Visibility]] [[da:sollys]] [[es:Luz diurna]] [[kk:Күн]] [[nl:Daglicht]] [[ru:День]] [[sv:Dagsljus]]