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A skylight providing internal illumination


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 allow an architect or engineer to quickly calculate benefits of a particular design. The human eye's response to light 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.[1] "Direct sunlight" reaches a site without being scattered within Earth's atmosphere. Sunlight that is scattered in the atmosphere is "diffused daylight". Sunlight reflected off walls and the ground also contributes to 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 vernal equinox at latitudes north of the Tropic of Cancer and south of the Tropic of Capricorn.[2]

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 the tropics in summertime), so they are effective at daylighting areas of the house adjacent to the windows. At higher latitudes during midwinter, light incidence is highly directional and casts long shadows. This may be partially ameliorated through light diffusion, 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.[2]



A conventional window
Clerestory windows



Windows grade into translucent walls (below).

Clerestory windows

Another important element in creating daylighting is the use of clerestory windows. These are high, vertically placed windows. They can be used to increase direct solar gain when oriented towards the equator. When facing toward the sun, clerestories and other windows may admit unacceptable glare. In the case of a passive solar house, clerestories may provide a direct light path to polar-side (north in the northern hemisphere; south in the southern hemisphere) rooms that otherwise would not be illuminated. Alternatively, clerestories can be used to admit diffuse daylight (from the north in the northern hemisphere) that evenly illuminates a space such as a classroom or office.

Often, clerestory windows also shine onto interior wall surfaces painted white or another light color. These walls are placed so as to reflect indirect light to interior areas where it is needed. This method has the advantage of reducing the directionality of light to make it softer and more diffuse, reducing shadows.

Sawtooth roof



Modern skylight




An atrium is a large open space located within a building. It is often used to light a central circulation or public area by daylight admitted through a glass roof or wall. Atria provide some daylight to adjacent working areas, but the amount is often small and does not penetrate very far.[7] The main function of an atrium is to provide a visual experience and a degree of contact with the outside for people in the working areas. The daylighting of successive storeys of rooms adjoining an atrium is interdependent and requires a balanced approach.[8] Light from the sky can easily penetrate the upper storeys but not the lower, which rely primarily on light reflected from internal surfaces of the atrium such as floor-reflected light.[9] The upper stories need less window area than the lower ones, and if the atrium walls are light in color the upper walls will reflect light toward the lower stories.[5]

Translucent walls

Glass brick wall, outdoors
Glass brick wall, indoors
Bottle wall


Increasing the amount of concrete, bottle walls embed bottles that run right through the wall, transmitting light. Concrete walls with glass prisms running through them have also been made.[] With the advent of cheaper optical fibers, fiber-optic concrete walls.[] Daylight (and shadow images) can then pass directly through a solid concrete wall, making it translucent; fiber optics will lead light around bends and over tens of meters.[13] Typically only a few percent of the light is transmitted (the percent transmittance is about half the percent of the surface that is fibers, and usually only ~5% fibers are used).[14][15]

Both glass and concrete conduct heat fairly well, when solid, so none of these walls insulate well. They are therefore often used outdoors, as a divider between two heated spaces (see images), or in very temperate climates.

Greenhouse walls (and roofs) are made to transmit as much light and as little heat as possible. They use a variety of materials, and may be transparent or translucent.

Remote distribution


Remote daylight distribution systems have losses, and the further they have to transmit the daylight and the more convoluted the path, the greater the inefficiency.[16] The efficiency of many remote distribution systems can also vary dramatically from clear to overcast skies. Nonetheless, where there is no other possibility of providing daylight to a space, remote distribution systems can be appreciated.[7]

Light reflectors and shelves

Light shelves
A light reflector





Daylight redirecting film bending light upwards


Prisms that used total internal reflection to throw light sideways, lighting the deeper portions of a room, later became popular. Early thick, slow-cooling cast glass prism tiles were often known as "luxfer tiles" after a major manufacturer.[18] They were and are used in the upper portions of windows, and some believe that they contributed to the trend from dark, subdivided Victorian interiors to open-plan, light-coloured ones.[]


Light tubes

Left: Diagram of a light tube.

Another type of device used is the light tube, also called a tubular daylighting device (TDD), which is placed into a roof and admits light to a focused area of the interior. These somewhat resemble recessed ceiling light fixtures. They do not allow as much heat transfer as skylights because they have less surface area.



Smart glass

Smart glass is the name given to a class of materials and devices that can be switched between a transparent state and a state which is opaque, translucent, reflective, or retro-reflective.[20] The switching is done by applying a voltage to the material, or by performing some simple mechanical operation. Windows, skylights, etc., that are made of smart glass can be used to adjust indoor lighting, compensating for changes of the brightness of the light outdoors and of the required brightness indoors.[21]

Solar lighting

The reflecting mirror of a heliostat



Solar street lights


Hybrid solar lighting



At night, ORNL HSL uses variable-intensity fluorescent lighting electronic control ballasts. As the sunlight gradually decreases at sunset, the fluorescent fixture is gradually turned up to give a near-constant level of interior lighting from daylight until after it becomes dark outside.

HSL may soon become an option for commercial interior lighting. It can transmit about half of the direct sunlight it receives.[22]







Architects and interior designers often use daylighting as a design element. Good daylighting requires attention to both qualitative and quantitative aspects of design.[7]


Utilizing natural light is one of the design aspects in architecture; In 1929, the French architect, Le Corbusier said that "The history of architectural material... has been the endless struggle for light... in other words, the history of windows." As he emphasized in his architecture (such as Notre Dame du Haut), daylighting has been a major architectural design element (See MIT Chapel and Church of the Light for examples). Not only the aesthetic aspects, the impact of daylighting on human health and work performance is also considered as qualitative daylighting.[23] The current studies show that lighting conditions in workplaces contribute to a variety of factors related to work satisfaction, productivity and well-being and significantly higher visual acceptance scores under daylighting than electrical lighting.[24] Studies have also shown that light has a direct effect on human health because of the way it influences the circadian rhythms.[25]


A well daylit space needs both adequate lighting levels and light that is well distributed. In the current building industry, daylighting is considered a building performance measure in green building certification programs such as LEED. Illuminating Engineering Society (IES) and the society of Light and Lighting (SLL) provide illuminance recommendation for each space type. How much daylighting contributes to the recommended lighting level determines daylighting performance of a building. There are two metrics that IES has approved to evaluate daylighting performance: Spatial Daylight Autonomy(sDA) and Annual Sunlight Exposure (ASE). sDA is a metric describing annual sufficiency of ambient daylight levels in interior environments.[26] See Daylight autonomy and LEED documentation sections for more details.

Evaluation method

Field measurements

In existing buildings, field measurements can be undertaken to evaluate daylighting performance. Illuminance measurements on a grid is a basic level to derive an average illuminance of a space. The spacing of the measurement points vary with project purposes. The height of these points depends on where the primary task is performed. In most office spaces, desk level (0.762m above the floor) will be measured. Based on measurements, average illuminance, maximum-to-minimum uniformity ratio, and average-to-minimum uniformity ratio will be calculated and compared to the recommended lighting level.[27] A diagnostic survey specific to lighting can be conducted to analyse the satisfaction of building occupants.[27]

Computational simulations



Daylight autonomy is the percentage of time that daylight levels are above a specified target illuminance within a physical space or building.[28] The calculation is based on annual data and the predetermined lighting levels. The goal of the calculation is to determine how long an individual can work in a space without requiring electrical lighting, while also providing optimal visual and physical comfort.[28]



Continuous daylight autonomy, is similar to daylight autonomy but partial credit is attributed to time steps when the daylight illuminance lies below the minimum illuminance level.[29] For example, if the target illuminance is 400 lux and the calculated value is 200 lux, daylight autonomy would give zero credit, while continuous daylight autonomy would give 0.5 credit (200/400 = 0.5). The benefit of continuous daylight autonomy is that it does not give a hard threshold of acceptable illuminance. Instead, it addresses the transition area--allowing for realistic preferences within any given space. For example, office occupants usually prefer to work at daylight below the illuminance threshold since this level avoids potential glare and excessive contrast.[29]

Useful illuminance

Useful daylight illuminance focuses on the direct sunlight that falls into a space. The useful daylight illuminance calculation is based on three factors--the percentage of time a point is below, between, or above an illuminance value. The range for these factors is typically 100-2,000 lux. Useful daylight illuminance is similar to daylight autonomy but has the added benefit of addressing glare and thermal discomfort.[30] The upper threshold is used to determine when glare or thermal discomfort is occurring and may need resolution.

LEED documentation


The LEED 2009 documentation is based upon the daylight factor calculation. The daylight factor calculation is based on uniform overcast skies. It is most applicable in Northern Europe and parts of North America.[32] Daylight factor is "the ratio of the illuminance at a point on a plane, generally the horizontal work plane, produced by the luminous flux received directly or indirectly at that point from a sky whose luminance distribution is known, to the illuminance on a horizontal plane produced by an unobstructed hemisphere of this same sky."[32]

LEED v4 daylighting standards are the most current as of 2014. The new standards are similar to the old standards, but also intend to "reinforce circadian rhythms, and reduce the use of electrical lighting by introducing daylight in the space.[33] Two options exist for achieving the maximum value of these two most recent points. One option is to use a computer simulation to demonstrate that a spatial daylight autonomy of 300 lux for at least 50% of the time, and an annual sunlight exposure of 1,000 lux for 250 occupied hours per year, exists in the space. Another option is to show that illuminance levels are between 300 lux and 3,000 lux between 9:00 a.m. and 3:00 p.m. on a clear day at the equinox for 75% or 90% of the floor area in the space.[33] The overall goal of the LEED v4 daylighting metrics is to analyze both the quantity and quality of the light, as well as to balance the use of glazing to ensure more light and less cooling load.

See also


  3. ^ Building for Energy Independence: Sun/Earth Buffering and Superinsulation. Community Builders. 1983. ISBN 978-0960442249.
  4. ^ "Energy Performance Label". The National Fenestration Rating Council. Retrieved 2019.
  5. ^ a b c CIBSE Lighting Guide 10: Daylighting and window design. CIBSE. 1999. ISBN 978-0-900953-98-9.
  6. ^ Asdrubali, F. (2003). "Lighting Research and Technology: "Daylighting performance of sawtooth roofs of industrial buildings "". Lighting Research and Technology. 35 (4): 343-359. doi:10.1191/1365782803li094oa.
  9. ^ Sharples, S. (1999). "Reflectance distributions and atrium daylight levels: a model study". Lighting Research and Technology. 31 (4): 165-170. doi:10.1177/096032719903100405.
  10. ^ "MVRDV integrates terra-cotta brick and glass for a facade in Amsterdam - Archpaper.com". archpaper.com. 2016-04-21. Retrieved .
  13. ^ "See-through concrete: LiTracon". The Future of Design. 14 November 2014.
  14. ^ SOUMYAJIT PAUL; AVIK DUTTA (October 2013). "TRANSLUCENT CONCRETE" (PDF). International Journal of Scientific and Research Publications. 3. ISSN 2250-3153.
  15. ^ "Anidolic Daylight Concentrator of Structural Translucent Concrete Envelope" (PDF). Sinberbest.berkeley.edu. Retrieved 2018.
  16. ^ Littlefair, P.J. (1990). "Review Paper: Innovative daylighting: Review of systems and evaluation methods". Lighting Research and Technology. 22: 1-17. doi:10.1177/096032719002200101.
  17. ^ Littlefair, P. J. (1995). "Light shelves: Computer assessment of daylighting". Lighting Research and Technology. 27 (2): 79-91. doi:10.1177/14771535950270020201.
  18. ^ a b "Prism Glass | glassian". Glassian.org. Retrieved .
  19. ^ Noblis. "EW-201014 Fact Sheet". Serdp-estcp.org. Retrieved .
  20. ^ Baetens, R.; Jelle, B. P.; Gustavsen, A. (2010). "Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review". Solar Energy Materials and Solar Cells. 94 (2): 87-105. doi:10.1016/j.solmat.2009.08.021. hdl:11250/2473860.
  21. ^ Lee, E.S.; Tavil, A. (2007). "Energy and visual comfort performance of electrochromic windows with overhangs". Building and Environment. 42 (6): 2439-2449. doi:10.1016/j.buildenv.2006.04.016.
  23. ^ Aries, M.B.C.; Aarts, M. P. J.; Van Hoof, J. (2015). "Daylight and health: A review of the evidence and consequences for the built environment". Lighting Research and Technology. 47: 6-27. doi:10.1177/1477153513509258.
  24. ^ Borisuit, A; Linhart, F. (2015). "Effects of realistic office daylighting and electric lighting conditions on visual comfort, alertness and mood". Lighting Research and Technology. 47 (2): 192-209. doi:10.1177/1477153514531518.
  28. ^ a b Reinhart, Christoph; Mardaljevic, John & Rogers, Zach (2006). "Dynamic Daylight Performance Metrics for Sustainable Building Design" (PDF). Leukos. 3 (1): 7-31. doi:10.1582/LEUKOS.2006.03.01.001. Retrieved 2014.
  29. ^ a b Jakubiec, J.A.; Reinhart, C.F. (2012). "The 'adaptive zone' - A concept for assessing discomfort glare throughout daylit spaces". Lighting Research and Technology. 44 (2): 149-170. doi:10.1177/1477153511420097.
  30. ^ Nabil, Azza; Mardaljevic, John (2006). "Useful daylight illuminances: A replacement for daylight factors". Energy and Buildings. 38 (7): 1858-1866. doi:10.1016/j.enbuild.2006.03.013.
  31. ^ "Daylight and views - daylight". U.S. Green Building Council. USGBC. Retrieved 2014.
  32. ^ a b Rea, Mark (2000). IESNA Lighting Handbook (9th ed.). Illuminating Engineering; 9 edition (July 2000). ISBN 978-0879951504.
  33. ^ a b "Daylight". U.S. Green Building Council. USGBC. Retrieved 2014.

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