Editing Daylighting (architecture) (section)

{{short description|Practice of placing openings and reflective surfaces so that sunlight can provide internal lighting}}
[[File:NYP LOC2.jpg|thumb|The main concourse of [[Pennsylvania Station (1910–1963)|Pennsylvania Station]], New York City, built in 1910. [[Train station|Railway station]]s of this era made extensive use of glass roofing to provide natural daylight to passengers below.]]
[[File:Daylighting - Skylight.jpg|thumb|upright|A [[skylight]] providing internal illumination]]
'''Daylighting''' is the practice of placing [[window]]s, [[skylight]]s, other openings, and [[Reflective surfaces (climate engineering)|reflective surfaces]] so that direct or indirect [[sunlight]] can provide effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy use. Energy savings can be achieved from the reduced use of artificial (electric) lighting or from [[passive solar]] heating. Artificial lighting energy use can be reduced by simply installing fewer electric lights where daylight is present or by automatically [[Dimmer|dimming]] or switching off electric lights in response to the presence of daylight{{snd}}a process known as [[daylight harvesting]].

The amount of daylight received in an internal space can be analyzed by measuring [[illuminance]] on a grid or undertaking a [[daylight factor]] calculation. Computer programs such as [[Radiance (software)|Radiance]] allow an architect or engineer to quickly calculate benefits of a particular design. The human eye's response to light [[Weber–Fechner law#Vision|is non-linear]], so a more even distribution of the same amount of light makes a room appear brighter.

The source of all daylight is the Sun. The proportion of direct to diffuse light impacts the amount and quality of daylight.<ref name="Daylighting Handbook 1">{{cite book |last=Reinhart |first=Christoph |date=2014 |title=Daylighting Handbook 1 |publisher=Christoph Reinhart |isbn=9780692203637}}</ref> "Direct sunlight" reaches a site without being [[Light scattering|scattered]] within [[Earth's atmosphere]]. Sunlight that is scattered in the atmosphere is "[[diffuse sky radiation|diffused daylight]]". Sunlight reflected off walls and the ground also contributes to daylighting. Each climate has different composition of these daylights and different [[cloud cover]]age, so daylighting strategies vary with site locations and climates. At latitudes north of the [[Tropic of Cancer]] and south of the [[Tropic of Capricorn]], there is no direct sunlight on the polar-side wall of a building between the autumnal equinox and the vernal equinox (that is, from the [[September equinox]] to the [[March equinox]] in the Northern Hemisphere, and from the March equinox to the September equinox in the [[Southern Hemisphere]].) In the [[Northern Hemisphere]], the north-facing wall is the "polar-side" and in the Southern Hemisphere, it is the south-facing wall.<ref name="The Science of Renewable Energy">{{cite book |last1=Spellman |first1=Frank |url=https://archive.org/details/scienceofrenewab0000spel |title=The Science of Renewable Energy |last2=Beiber |first2=Revonna |date=2011 |publisher=CRC Press; 1 edition |isbn=978-1439825020 |url-access=registration}}</ref>

Traditionally, houses were designed with minimal windows on the polar side, but more and larger windows on the equatorial side (south-facing wall in the Northern Hemisphere and north-facing wall in the Southern Hemisphere).<ref>[http://www.nrel.gov/learning/re_passive_solar.html] {{webarchive|url=https://web.archive.org/web/20090117213701/http://www.nrel.gov/learning/re_passive_solar.html|date=January 17, 2009}}</ref> Equatorial-side windows receive at least some direct sunlight on any sunny day of the year (except in the [[tropics]] in [[summer]]), so they are effective at daylighting areas of the house adjacent to the windows. At higher latitudes during [[Winter solstice|midwinter]], light incidence is highly directional and casts long shadows. This may be partially ameliorated through [[light diffusion]], [[Light tube|light pipes or tubes]], and through somewhat reflective internal surfaces. At fairly low latitudes in summertime, windows that face east and west and sometimes those that face toward the nearer pole receive more sunlight than windows facing toward the equator.<ref name="The Science of Renewable Energy"/>