Last updated
Skylight in the rotunda of Centro Cultural Banco do Brasil in Rio de Janeiro. Cupula do Centro Cultural Banco do Brasil (Rio de Janeiro).jpg
Skylight in the rotunda of Centro Cultural Banco do Brasil in Rio de Janeiro.
Large skylighting element, in the Star Ferry Pier, Hong Kong. HK Central Star Ferry Pier 7 Shop L Restaurant WaterMark a2.jpg
Large skylighting element, in the Star Ferry Pier, Hong Kong.
Oculus of the Pantheon, an open skylight. Oculus of the Pantheon.jpg
Oculus of the Pantheon, an open skylight.

A skylight is a light-transmitting structure that forms all or part of the roof space of a building for daylighting purposes.

Roof covering on the uppermost part of a building or vehicle

A roof is part of a building envelope. It is the covering on the uppermost part of a building or shelter which provides protection from animals and weather, notably rain or snow, but also heat, wind and sunlight. The word also denotes the framing or structure which supports that covering.

Daylighting the practice of placing windows or other openings

Daylighting is the practice of placing windows, skylights, other openings, and reflective surfaces so that 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 dimming/switching off electric lights in response to the presence of daylight – a process known as daylight harvesting.



Open skylights were used in Ancient Roman architecture, such as the oculus of the Pantheon. Glazed 'closed' skylights have been in use since the Industrial Revolution made advances in glass production manufacturing. Mass production units since the mid-20th century have brought skylights to many uses and contexts. Energy conservation has brought new motivation, design innovation, transmission options, and efficiency rating systems for skylights.

Oculus architectural feature

An oculus is a circular opening in the center of a dome or in a wall. Originating in antiquity, it is a feature of Byzantine and Neoclassical architecture. It is also known as an œil de boeuf from the French, or simply a "bull's-eye".

Pantheon, Rome Roman temple in Rome

The Pantheon is a former Roman temple, now a church, in Rome, Italy, on the site of an earlier temple commissioned by Marcus Agrippa during the reign of Augustus. It was completed by the emperor Hadrian and probably dedicated about 126 AD. Its date of construction is uncertain, because Hadrian chose not to inscribe the new temple but rather to retain the inscription of Agrippa's older temple, which had burned down.

Industrial Revolution Mid-20th-to-early-21th-century period; First Industrial Revolution evolved into the Second Industrial Revolution in the transition years between 1840 and 1870

The Industrial Revolution was the transition to new manufacturing processes in Europe and the US, in the period from about 1760 to sometime between 1820 and 1840. This transition included going from hand production methods to machines, new chemical manufacturing and iron production processes, the increasing use of steam power, the development of machine tools and the rise of the factory system. The Industrial Revolution also led to an unprecedented rise in the rate of population growth.

Prior to the Industrial Revolution, it was France that probably had the leading technology in architectural glass. One of the earliest forms of the glass skylight can be seen at the Palace of Versailles in the Galerie des Batailles, which was added onto the existing palace by Louis Philippe in the year 1830. Another form that displays early sky lighting technology is the Halle aux blés (Paris) built in 1763-67. This form of natural overhead lighting allowed for illumination while decoration could cover the entire interior wall, and it is the option least obstructed by other buildings. This means that sky lighting as we know it, in many forms today, was probably pioneered in France during the early 18th century or late 17th century. According to architectural glass, the earliest functional skylights would have been formed by either glass casting, crown glass (window), cylinder blown sheet, and machine drawn cylinder sheet, or fourcault process.

France Republic with mainland in Europe and numerous oversea territories

France, officially the French Republic, is a country whose territory consists of metropolitan France in Western Europe and several overseas regions and territories. The metropolitan area of France extends from the Mediterranean Sea to the English Channel and the North Sea, and from the Rhine to the Atlantic Ocean. It is bordered by Belgium, Luxembourg and Germany to the northeast, Switzerland and Italy to the east, and Andorra and Spain to the south. The overseas territories include French Guiana in South America and several islands in the Atlantic, Pacific and Indian oceans. The country's 18 integral regions span a combined area of 643,801 square kilometres (248,573 sq mi) and a total population of 67.3 million. France, a sovereign state, is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre. Other major urban areas include Lyon, Marseille, Toulouse, Bordeaux, Lille and Nice.

Architectural glass

Architectural glass is glass that is used as a building material. It is most typically used as transparent glazing material in the building envelope, including windows in the external walls. Glass is also used for internal partitions and as an architectural feature. When used in buildings, glass is often of a safety type, which include reinforced, toughened and laminated glasses.

Skylight window in the ceiling-roof

A skylight is a light-transmitting structure that forms all or part of the roof space of a building for daylighting purposes.

[1] [2]


Skylighting types include roof windows, unit skylights, tubular daylighting devices (TDDs), sloped glazing, and custom skylights. Uses include:

Roof window

A roof window is an outward opening window that is incorporated as part of the design of a roof. Often confused with a skylight, a roof window differs in a few basic ways. A roof window is often a good option when there is a desire to allow both light and fresh air into the space.

Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption. This approach works either by preventing heat from entering the interior or by removing heat from the building. Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components, rather than mechanical systems to dissipate heat. Therefore, natural cooling depends not only on the architectural design of the building but on how the site's natural resources are used as heat sinks. Examples of on-site heat sinks are the upper atmosphere, the outdoor air (wind), and the earth/soil.

The skylight of Munster's shopping mall "Arkaden". Skylight Munster Arkaden.JPG
The skylight of Münster's shopping mall "Arkaden".
Fixed unit skylight, roof view. Skylight w cuppola.jpg
Fixed unit skylight, roof view.
Fixed unit skylights, interior view. Velux GGL-7 Center-Pivot Roof Window, 1986 Model.jpg
Fixed unit skylights, interior view.
Open skylight

An unglazed hole in a roof.

Fixed unit skylight

A fixed skylight consists of a structural perimeter frame supporting glazing infill (the light-transmitting portion, which is made primarily of glass or plastic). A fixed skylight is non-operable, meaning there is no ventilation.

Operable skylight

An operable (venting) unit skylight uses a hinged sash attached to and supported by the frame. When within reach of the occupants, this type is also called a roof window.

Retractable skylight

A retractable skylight rolls - on a set of tracks - off the frame, so that the interior of the facility is entirely open to the outdoors, i.e., not impeded by a hinged skylight. The terms retractable skylight and retractable roof are often used interchangeably, though skylight implies a degree of transparency.

Tubular daylight device

Active daylighting uses a tubular daylighting device—TDD. It is a roof-mounted fixed unit skylight element, condensing sunlight, distributed by a light conveying optic conduit to a light diffusing element. Being small in diameter, they can be used for daylighting smaller spaces such as hallways, and bounce light in darker corners of spaces. TDDs harvest daylight through a roof-mounted dome with diameters ranging from about 10 inches for residential applications to 22 inches for commercial buildings. Made from acrylic or polycarbonate formulated to block ultraviolet rays, the dome captures and redirects light rays into an aluminum tubing system that resembles ductwork. [3] Image:Skylight on the roof terrace of Liverpool Central Library (2).JPG|TDD skylight on the roof terrace of Liverpool Central Library

Sloped glazing

Sloped glazing differs from other “skylights” in that one assembly contains multiple infill panels in a framing system, usually designed for a specific project and installed in sections on site.

Pavement lights

Pavement lights are walk-on skylights. They are set into sidewalks, open areas, and well-lit interior floors.

Prism lights

Prism lights are sometimes used as skylights; they redirect the light passing through.

Solar architecture

Skylights are widely used in designing daylighting for residential, public, and commercial buildings. Increased daylighting can result in less electrical lighting use and smaller sized window glazing (sidelighting), saving energy, lowering costs, and reducing environmental impacts. Daylighting can cut lighting energy use in some buildings by up to 80%. [4]

Toplighting (skylights) works well with sidelighting (windows) to maximize daylighting:

  1. toplighting is able to bring light into centralized areas of a building
  2. daylight is available throughout the day from both ambient lighting from the sky and direct exposure to the sun.
  3. modern transparent and/or translucent glazing can be utilized to avoid glare, aid in capturing sunlight at low angles and diffuse light to wider areas of floor space.

Even on overcast days, toplighting from skylights is three to ten times more efficient than sidelighting. [5]



Many recent[ when? ] advances in both glass and plastic infill systems have greatly benefited all skylight types. Some advances increase thermal performance, some are focused on preserving and utilizing daylight potential, and some are designed to enhance strength, durability, fire resistance and other performance measures.

Contemporary skylights using glass infill (windows) typically use sealed insulating glass units (IGU) made with two panes of glass. These types of products are NFRC-ratable for visible transmittance. Assemblies with three panes can sometimes be cost-justified in the coldest climate zones, but they lose some light by adding the third layer of glass.

Glass units typically include at least one low emissivity (Low-E) coating applied to one or more glass surfaces to reduce the U-factor and especially SHGC by suppressing radiant heat flow. Many varieties of Low-E coatings also reduce daylight potential to different degrees. High purity inert gas is frequently used in the space(s) between panes, and advances in thermally efficient glass spacing and supporting elements can further improve thermal performance of glass-glazed skylight assemblies.


Plastic glazing infill is commonly used in many skylights and TDDs. These assemblies typically contain thermally formed domes, but molded shapes are not uncommon. Domed skylights are typically used on low slope roofs. The dome shape allows for shedding of water and burning embers.

Plastics used in skylights are UV stabilized and may feature other advances to improve thermal properties. Lack of accepted standards for measuring light transmittance is a disadvantage for comparing and choosing skylights with plastic glazing.

Acrylic is the most common plastic glazing used for dome skylights. However, Polycarbonate and Copolyester materials are also used as glazing, where additional properties such as impact resistance may be required. [6]

Rating systems

NFRC — rating for visible transmittance

U-factor — expresses the heat loss performance of any building assembly.

SHGC—Solar Heat Gain Coefficient — measures the assembly’s transfer of heat from outside to inside that is caused by sunlight.

These properties are labeled in the U.S. as a decimal between zero and one, with lower numbers indicating lower heat transfer rates. Depending on the geographic region, optimal U-factor and SHGC performance will vary. In the sunny southern climate zones, a lower SHGC is more important than lower U-factor. In the cooler northern climate zones, lower U-factor is more important, and higher SHGC can be justified.

In selection of skylights, a balance is sought between low U-factor and optimal SHGC values, while preserving enough daylight supply to minimize artificial light use. Automatic light sensing controls for electric lighting maximize energy savings.


A study concluded that students have significantly higher test scores in classrooms that optimize daylighting, than classrooms that do not. [7] Other studies show that daylight positively affects physiological and psychological well-being, which can increase productivity in many contexts, such as sales in retail spaces.[ citation needed ]

In terms of cost savings, U.S. DOE reported that many commercial buildings can reduce total energy costs by up to one-third through the optimal use of daylighting. The majority of commercial warehouses and 'big box stores' built in recent years have used skylights extensively for energy/costs savings.

See also

Related Research Articles

Window transparent or translucent opening

A window is an opening in a wall, door, roof or vehicle that allows the passage of light, sound, and air. Modern windows are usually glazed or covered in some other transparent or translucent material, a sash set in a frame in the opening; the sash and frame are also referred to as a window. Many glazed windows may be opened, to allow ventilation, or closed, to exclude inclement weather. Windows often have a latch or similar mechanism to lock the window shut or to hold it open by various amounts.

Trombe wall

A Trombe wall is a passive solar building design where a wall is built on the winter sun side of a building with a glass external layer and a high heat capacity internal layer separated by a layer of air. Light close to UV in the electromagnetic spectrum passes through the glass almost unhindered then is absorbed by the wall that then re-radiates in the far infrared spectrum which does not pass back through the glass easily, hence heating the inside of the building. Trombe walls are commonly used to absorb heat during sunlit hours of winter then slowly release the heat over night. The essential idea was first explored by Edward S. Morse and patented by him in 1881. In the 1960s it was fully developed as an architectural element by French engineer Félix Trombe and architect Jacques Michel.

Passive solar building design

In passive solar building design, windows, walls, and floors are made to collect, store, reflect, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer. This is called passive solar design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.

Thermal mass

In building design, thermal mass is a property of the mass of a building which enables it to store heat, providing "inertia" against temperature fluctuations. It is sometimes known as the thermal flywheel effect. For example, when outside temperatures are fluctuating throughout the day, a large thermal mass within the insulated portion of a house can serve to "flatten out" the daily temperature fluctuations, since the thermal mass will absorb thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy back when the surroundings are cooler, without reaching thermal equilibrium. This is distinct from a material's insulative value, which reduces a building's thermal conductivity, allowing it to be heated or cooled relatively separate from the outside, or even just retain the occupants' thermal energy longer.

Sunroom room having glass roof and walls, typically attached to a house

A sunroom, also frequently and traditionally denominated a solarium, is a room that is built, either attached to, or integrated into, the primary building, such as a residence or office, that permits abundant daylight and views of the landscape while sheltering from adverse weather. Sunroom and solarium have the same denotation: solarium is Latin for "place of sun[light]". Solaria of various forms have been erected throughout European history. Presently, the sunroom or solarium is popular in Europe, Canada, the United States, Australia, and New Zealand. Sunrooms may feature passive solar building design to heat and illuminate them.

A thermal break or thermal barrier is an element of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy between conductive materials. The opposite of a thermal barrier is a thermal bridge.

Thermal transmittance, also known as U-value, is the rate of transfer of heat through one square meter of a structure, divided by the difference in temperature across the structure. It is expressed in watts per square metre kelvin, W/m²K, or W.m−2.K−1. Well-insulated parts of a building have a low thermal transmittance whereas poorly insulated parts of a building have a high thermal transmittance. Losses due to thermal radiation, thermal convection and thermal conduction are taken into account in the U-value. Although it has the same units as heat transfer coefficient, thermal transmittance is different in that the heat transfer coefficient is used to solely describe heat transfer in fluids while thermal transmittance is used to simplify an equation that has several different forms of thermal resistances.

Light tube architectural element

Light tubes are physical structures used for transmitting or distributing natural or artificial light for the purpose of illumination, and are examples of optical waveguides.

Building insulation material used to thermally insulate buildings

Building insulation is any object in a building used as insulation for any purpose. While the majority of insulation in buildings is for thermal purposes, the term also applies to acoustic insulation, fire insulation, and impact insulation. Often an insulation material will be chosen for its ability to perform several of these functions at once.

Solar gain

Solar gain refers to the increase in thermal energy of a space, object or structure as it absorbs incident solar radiation. The amount of solar gain a space experiences is a function of the total incident solar irradiance and of the ability of any intervening material to transmit or resist the radiation.

Roof lantern architectural element

A roof lantern is a daylighting architectural element. Architectural lanterns are atop a larger roof and provide natural light into the space or room below. In contemporary use it is an architectural skylight structure. The term 'roof top lantern' is used to describe the lighted decorative lanterns atop taxi cabs in Japan, designed to reflect the cultural heritage of Japanese paper lanterns.

Passive daylighting is a system of both collecting sunlight using static, non-moving, and non-tracking systems and reflecting the collected daylight deeper inside with elements such as light shelves. Passive daylighting systems are different from active daylighting systems in that active systems track and/or follow the sun, and rely on mechanical mechanisms to do so.

Shading coefficient (SC) is a measure of thermal performance of a glass unit in a building.

Daylight harvesting systems use daylight to offset the amount of electric lighting needed to properly light a space, in order to reduce energy consumption. This is accomplished using lighting control systems that are able to dim or switch electric lighting in response to changing daylight availability. The term Daylight Harvesting has become the standard in the fields of lighting, sustainable architecture, and active daylighting industries.


An Eco-house is an environmentally low-impact home designed and built using materials and technology that reduces its carbon footprint and lowers its energy needs.

Insulated glazing

Insulating glass (IG), more commonly known as double glazing, consists of two or three glass window panes separated by a vacuum or gas filled space to reduce heat transfer across a part of the building envelope.

Retrofitting Building M: University of Reunion Island, France

Building M is located on Reunion Island on the outskirts of the town of Le Tampon at a high altitude and benefits from a tropical climate. From 1972 to 1991, Building M housed an army school. In 1994, the South Campus of the University of Reunion Island was created and the army buildings were converted into classrooms for the future students.

The David and Lucile Packard Foundation Headquarters is a building in Northern California, at the south end of San Francisco Bay. It is the headquarters of the David and Lucile Packard Foundation, created in 1964 by David Packard and his wife Lucile Salter Packard, one of the top 100 grantmaking foundations in the United States,with the goals of improving the lives of children, enabling the creative pursuit of science, advancing reproductive health, and conserving and restoring the Earth’s natural systems. The David and Lucile Packard Foundation Headquarters is designed to be the largest net zero energy building in California, and it has successfully reduced the energy use by 65% over conventional buildings.


  1. Sunlighting as Forgiver for Architecture, Lam
  2. wikipedia
  3. Lau, Wanda (Feb 6, 2012). "Lighten Up Tubular daylighting devices turn natural light into a deployable technology". EcoBuilding Pulse. Retrieved April 3, 2014.
  4. U.S. Department of Energy (DOE): Federal Energy Management Program; toplighting_final_report
  5. AAMA: Daylighting Fact Sheet
  6. AAMA Skylight Council
  7. study of 21,000 students.