DAYLIGHT

'Daylight' or 'the light of day' is the combination of all direct and indirect sunlight outdoors during the daytime (and perhaps twilight). This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected from the Earth and terrestrial objects. ''Daytime'' is the period of time each day when daylight occurs. While perceived moonlight is in fact light from the sun reflected towards the Earth, and is hence to be considered "indirect sunlight", it is not considered daylight as it occurs outside of the hours that one would consider "daytime".
Daylight is present, to some degree, whenever that 50% of the earth is in view of the sun, but the outdoor illuminance can vary from 100,000 lux for direct sunlight at noon, which may cause eye discomfort, to less than 5 lux for the thickest storm clouds with the sun at the horizon, which may make shadows from distant street lights visible. It may be darker under unusual circumstances such as a solar eclipse or very high levels of atmospheric smoke.
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 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.

Contents

Daylight intensity in different conditions

Daylight intensity in the Solar System

See also

Notes

External links

Daylight intensity in different conditions

Sky light intensity at night in various conditions is given for comparison.

Illuminance	Example
0.00005 lux	Starlight
0.0001 lux	Moonless overcast night sky
0.001 lux	Moonless clear night sky
0.01 lux	Quarter Moon
0.25 lux	Full Moon on a clear night[1]
|Moonlight[2]
400 lux	Sunrise or sunset on a clear day.
32000 lux	Sunlight on an average day (min.)
100000 lux	Sunlight on an average day (max.)

Daylight intensity in the Solar System

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 and Pluto) follows (from data in [1]):

Planet	Distance from Sun (AU)	Relative solar intensity
Mercury	0.387	6.68
Venus	0.723	1.913
Earth and Moon	1	1
Mars	1.524	0.431
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.
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.

See also

★ Rights of Light

★ Twilight

★ Moonlight

★ Daylight saving time

Notes

1. Petzl reference system for lighting performance
2. Interference of moonlight with the photoperiodic measurement of time by plants, and their adaptive reaction, , Erwin, Bunning, Proceedings of the National Academy of Sciences of the United States of America, 1969

External links

★ The Daylight Site

★ Royal Institution of Chartered Surveyors - Rights to Light Determination Homepage

★ Daylight Chart shows sunrise and sunset times in a chart, for any location in the world.

★ Daylight Google Map and Satellite View