From en.wikipedia.org:
[Natural light during the daytime] [Daylight (disambiguation)]
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.
** 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 light]]s 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,<ref>[url=http://www.perryton.com/black.htm ] and volcanic ash.[1]
** Intensity in different conditions
{| class="wikitable" ! Illuminance !! Example |- | 120,000 lux||Brightest
sunlight |- | 111,000 lux||Bright sunlight |- | 109,880 lux||AM 1.5 global
solar spectrum sunlight (= 1,000.4 W/m<sup>2</sup>)[2][date=October 2022] |- |
20,000 lux||Shade illuminated by entire clear blue sky, midday |- |
1,000–2,000 lux||Typical overcast day, midday |- | 400 lux||Sunrise or sunset
on a clear day (ambient illumination) |- | <200 lux||Extreme of thickest storm
clouds, midday |- | 40 lux||Fully overcast, sunset/sunrise |- | <1
lux||Extreme of thickest storm clouds, sunset/rise |}
For comparison, nighttime illuminance levels are:
{| class="wikitable" ! Illuminance !! Example |- | <1
lux||[[Moonlight]],<ref>[last=Bunning ][bot=medic] clear night sky |- | 0.25
lux||A full Moon, clear night sky[3][4] |- | 0.01 lux||A quarter Moon, clear
night sky |- | 0.002 lux||Starlight, clear moonless night sky, including
airglow<ref name="radfaq"/> |- | 0.0002 lux||Starlight, clear moonless night
sky, excluding airglow<ref name="radfaq"/> |- | 0.00014 lux||Venus at
brightest,<ref name="radfaq"/> clear night sky |- | 0.0001 lux||Starlight,
overcast moonless night sky<ref name="radfaq"/> |}
For a table of approximate daylight intensity in the Solar System, see
sunlight.
** See also
{{cmn|
- Artificial sky
- Color temperature
- Daylight harvesting
- Daylight saving time
- Daylighting
- [Daytime]
- Moonlight
- Right to light
- Twilight
}}
** References
[Reflist]
** External links
- Length of Day and Twilight – Deriving the formulas to calculate the length of day (see http://www.gandraxa.com/length_of_day.xml)
[Parts of a day] [Authority control]
Category:Atmospheric optical phenomena Category:Light Category:Parts of a day
Category:Visibility