Iluminación natural es la práctica de colocar las ventanas u otras aberturas y superficies reflectantes a fin de que durante el día la luz natural ofrezca una eficaz iluminación interior. Se presta especial atención a la iluminación natural en el diseño de un edificio, cuando el objetivo es maximizar el confort visual y para reducir el uso de energía eléctrica. El ahorro de energía puede lograrse, ya sea a partir de la reducción del uso de la iluminación artificial, a partir de energía solar pasiva o de calefacción o refrigeración. Iluminación natural es un término técnico dado por siglos, independientemente de la geografía y la cultura. Durante el siglo XX los arquitectos encontraron que se estaba haciendo un uso inadecuado y reformularon el concepto, generando una línea de investigación que se volcó en bibliografía específica. En el presente siglo con cuestiones tales como el calentamiento global y la necesidad de reducir drásticamente la demanda de energía el tema tiene una gran vigencia. No hay luz directa del sol sobre la pared lateral polar de un edificio desde el equinoccio de otoño al equinoccio de primavera en las partes del mundo al norte del Trópico de Cáncer y en partes del mundo al sur del Trópico de Capricornio. Tradicionalmente, en estos sitios con cielos mayormente nublados, las casas fueron diseñadas con un mínimo de ventanas en el lado polar, pero más grandes en el lado ecuatorial. El lado soleado de las ventanas, al menos, reciben la luz directa del sol en cualquier día soleado del año. Por lo que son eficaces en las áreas de iluminación natural de la casa junto a las ventanas. Aun así, durante mediados del invierno, la incidencia de luz es muy direccional y arroja sombras. Esto puede ser parcialmente mejorado a través de la luz y la difusión a través de un poco de reflexión de las superficies internas.

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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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