Daylighting

Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides 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 because daylight is present, or by dimming/switching electric lights automatically in response to the presence of daylight, a process known as daylight harvesting.

Daylighting is a technical term given to a common centuries-old, geography and culture independent design basic when "rediscovered" by 20th century architects. The amount of daylight received in an internal space can be analyzed by measuring illuminance on a grid or undertaking a daylight factor calculation. Today, the use of software, such as Radiance, can allow an architect or engineer to quickly undertake complex calculations to review the benefit of a particular design.

The source of all daylight is the sun. The proportion of direct to diffuse light impacts the amount and quality of daylight. Solar radiation that reaches a site without being scattered within the earth’s atmosphere is called direct sunlight. In contrast, light that is scattered in the atmosphere is referred to as diffused daylight. Ground reflected light also contributes to the daylight. Each climate has different composition of these daylights and different cloud coverage, so daylighting strategies vary with site locations and climates. There is no direct sunlight on the polar-side wall (north-facing wall in the northern hemisphere and south-facing wall in the southern hemisphere) of a building from the autumnal equinox to the spring equinox in parts of the globe north of the Tropic of Cancer and in part of the globe south of the Tropic of Capricorn. 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). Equatorial-side windows receive at least some direct sunlight on any sunny day of the year (except in tropical latitudes in summertime) so they are effective at daylighting areas of the house adjacent to the windows. Even so, during mid-winter, light incidence is highly directional and casts deep shadows. This may be partially ameliorated through light diffusion, light pipes or tubes, and through somewhat reflective internal surfaces. In fairly low latitudes in summertime, windows that face east and west and sometimes those that face toward the pole receive more sunlight than windows facing toward the equator.

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