
Daylight is the combination of all direct and indirect
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
during the
daytime
Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's hemis ...
. This includes direct
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
,
diffuse sky radiation, and (often) both of these reflected by
Earth and terrestrial objects, like
landform
A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, ...
s and buildings. Sunlight
scattered
Scattered may refer to:
Music
* ''Scattered'' (album), a 2010 album by The Handsome Family
* "Scattered" (The Kinks song), 1993
* "Scattered", a song by Ace Young
* "Scattered", a song by Lauren Jauregui
* "Scattered", a song by Green Day from ' ...
or reflected by
astronomical object
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
s is generally not considered daylight. Therefore, daylight excludes
moonlight
Moonlight consists of mostly sunlight (with little earthlight) reflected from the parts of the Moon's surface where the Sun's light strikes.
Illumination
The intensity of moonlight varies greatly depending on the lunar phase, but even the ful ...
, 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
The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
. (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
The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the ...
for direct
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
at
noon, which may cause eye
pain
Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
, to less than 5
lux
The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the ...
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
A street light, light pole, lamp pole, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or path. Similar lights may be found on a railway platform. When urban electric power distribution ...
s visible. It may be darker under unusual circumstances like a
solar eclipse
A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of the Earth, totally or partially. Such an alignment occurs during an eclipse season, approximately every six month ...
or very high levels of atmospheric
particulates, which include smoke (see
New England's Dark Day), dust, and volcanic ash.
Intensity in different conditions
For comparison, nighttime illuminance levels are:
For a table of approximate daylight intensity in the
Solar System, see
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
.
See also
References
External links
Daylight Chartshows sunrise and sunset times in a chart, for any location in the world
Length of Day and Twilight – Deriving the formulas to calculate the length of day
{{Authority control
Atmospheric optical phenomena
Light
Parts of a day
Visibility