Search: in
Daylight
Daylight in Encyclopedia Encyclopedia
  Tutorials     Encyclopedia     Videos     Books     Software     DVDs  
       





Daylight

World map showing the areas of the Earth receiving daylight around 13:00 UTC, April 2nd.
World map showing the areas of the Earth receiving 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. 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.

Contents


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 here). 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] or volcanic ash.[2]

Daylight intensity in different conditions

Artificial image showing a nightfall over Europe and Africa. The solar terminator is shown for UTC July 5, 2005 18.45.00
Artificial image showing a nightfall over Europe and Africa. The solar terminator is shown for UTC July 5, 2005 18.45.00

Illuminance Example
120,000 lux Brightest sunlight
110,000 lux Bright sunlight
20,000 lux Shade illuminated by entire clear blue sky, midday
10,000 - 25,000 lux Typical overcast day, midday
Extreme of darkest storm clouds, midday
400 lux Sunrise or sunset on a clear day (ambient illumination).
40 lux Fully overcast, sunset/sunrise
Extreme of darkest storm clouds, sunset/rise

For comparison, nighttime illuminance levels are:

Illuminance Example
Moonlight[3]
0.25 lux Full Moon on a clear night[4][5]
0.01 lux Quarter Moon
0.002 lux Starlight clear moonless night sky including airglow[4]
0.0002 lux Starlight clear moonless night sky excluding airglow[4]
0.00014 lux Venus at brightest[4]
0.0001 lux Starlight overcast moonless night sky[4]

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

Effects

Daylight in January. At the polar regions there are extreme differences in the amount of daylight in summer and winter.
Daylight in January. At the polar regions there are 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 depression specifically linked to limited daylight are referred to as seasonal affective disorder.

Daylighting is lighting an indoor space with openings such as windows and skylights 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. The amount of daylight received into an indoor space or room is defined as a daylight factor, being the ratio between the measured internal and external light levels. Artificial lighting energy use can be reduced by simply installing fewer electric lights because daylight is present, or by dimming/switching electric lights automatically in response to the presence of daylight, a process known as daylight harvesting.

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. In some filmmaking locations, such as Sweden, there is too much light due to long summer days. As a result, in films like Marianne, night scenes have to be shot during the daylight hours and digitally altered later.

See also

  • Twilight
  • Moonlight
  • Daylight saving time
  • Daylighting
  • Daytime (astronomy)
  • Right to light
  • Day length

Notes

External links

ar: az:G n be: de:Tageslicht myv: ( ) es:Luz diurna fa: fr:Lumi re du jour gan: he: kn: krc: ( ) kk: lt:Diena mn: nl:Daglicht ja: nn:Dagslys pl:Dzie ru: sv:Dagsljus tt: th: uk: ur: zh-yue: bat-smg:D ina zh:






Source: Wikipedia | The above article is available under the GNU FDL. | Edit this article



Search for Daylight in Tutorials
Search for Daylight in Encyclopedia
Search for Daylight in Videos
Search for Daylight in Books
Search for Daylight in Software
Search for Daylight in DVDs
Search for Daylight in Store




Advertisement




Daylight in Encyclopedia
Daylight top Daylight

Home - Add TutorGig to Your Site - Disclaimer

©2011-2013 TutorGig.info All Rights Reserved. Privacy Statement