# Skylight

A skylight (sometimes called a rooflight) is a light-permitting structure or window, usually made of transparent or translucent glass, that forms all or part of the roof space of a building for daylighting and ventilation purposes.

## History

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, when advances in glass manufacturing made them practical. Since the mid-20th century, mass production of skylights has brought them to many more uses and contexts. Energy conservation has brought new motivation for installing skylights, design innovations (including options in light transmission), and skylight efficiency ratings.

## Description

Skylighting types include roof windows, unit skylights, tubular daylighting devices (TDDs), sloped glazing, and custom skylights. Uses include:
* daylighting elements used to allow direct and/or indirect sunlight, via toplighting.
* providing a visual connection to the outdoor environment to interior occupants.
* sustainable building—passive solar heating, and with operable units; ventilation for passive cooling and fresh air exchange.

### Open skylight

An unglazed hole in a roof.

### Fixed unit skylight

* Solar-powered venting skylight in Southern California
* The skylight of Münster's shopping mall
* Fixed unit skylight, roof view
* Fixed unit skylights, interior view
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 large (20' x 20') steel and glass retractable skylight, seen from the roof. Note the steel tracks that the skylight rolls on, to retract.
* The same retractable skylight, seen from the interior. This is a bi-parting skylight, meaning that it parts in the middle to open.
* This ridge skylight wraps over the highest point of the roof – the ridgeline.
* This is that same skylight, from the inside. Steel allows large spans, without a grid of supporting tubes and cables.
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 daylight device—TDD
* TDD skylight on the roof terrace of Liverpool Central Library
Active daylighting uses a tubular daylighting device (TDD). Solar tubes, sun tunnels, or tubular skylights consist of 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.

### 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 as laylights.

### Prism lights

Prism lights are sometimes used as skylights; they redirect the light passing through. Skylight A skylight (also known as a rooflight) is a structure or window installed on the roof of a building, designed to allow natural light to enter the interior space. Typically made of transparent or translucent materials like glass or polycarbonate, skylights are used for daylighting and, in some cases, ventilation. They are a key feature in both residential and commercial architecture, contributing to energy efficiency and aesthetic appeal.[1]
History The use of daylighting can be traced back to ancient civilizations. In Ancient Roman architecture, open sustainable building, such as the oculus in the Pantheon, were used to provide light and ventilation.[2] During the Industrial Revolution, advancements in glass manufacturing made glazed skylights more practical and accessible, leading to their widespread adoption in buildings.[3]
In the mid-20th century, mass production techniques made more affordable and versatile, allowing them to be used in a variety of architectural styles. Today, skylights are not only functional but also play a significant role in sustainable building design, with innovations aimed at improving energy efficiency and light control.[4] Types of Skylights Skylights come in several types, each suited to specific architectural needs:
Fixed Skylights: Non-operable depatie roofing's solely for allowing light into a space.
Ventilating Skylights: Operable skylights that can be opened to provide ventilation in addition to light.
Tubular Daylighting Devices (TDDs): Compact, reflective tubes that channel sunlight into interior spaces, ideal for smaller areas or rooms with limited roof space.
Custom Skylights: Tailored designs for unique architectural requirements, often used in large commercial or luxury residential projects.
Sloped Glazing: Angled glass installations commonly used in greenhouses, atriums, or modern architectural designs.[5]
Uses and Benefits Skylights serve multiple purposes in building design, including:
Daylighting: Reducing the need for retractable roof by allowing natural light to illuminate interior spaces.
Energy Efficiency: Contributing to passive solar heating in winter and reducing cooling loads in summer when properly designed.
Ventilation: Operable Active daylighting can improve indoor air quality by allowing fresh air to circulate.
Aesthetic Appeal: Active daylighting of a space by create connection to the outdoor and providing views of the sky.
Health Benefits: Exposure to natural light has been shown to improve mood, productivity, and overall well-being.[6]
Challenges and Considerations While skylights offer numerous benefits, they also come with potential challenges:
Heat Gain and Loss: Poorly insulated can lead to increased energy costs due to heat transfer. Glare: Direct sunlight entering through skylights can cause glare, which may be uncomfortable for occupants. Leakage: Improper installation can result in water leakage during rain. Maintenance: Skylights require regular cleaning and inspection to ensure optimal performance and longevity. Innovations in Skylight Technology Recent advancements in skylight technology have addressed many of these challenges: Energy-Efficient Glazing: Double or triple-glazed skylights with low-emissivity (Low-E) coatings to reduce heat transfer. Smart Skylights: Automated skylights with sensors that adjust based on weather conditions or time of day. Dynamic Glazing: Glass that can change its transparency to control light and heat levels. Solar-Powered Skylights: Skylights equipped with solar panels to power ventilation systems or other features.[8] Environmental Impact Skylights play a significant role in sustainable architecture by reducing the need for artificial lighting and improving energy efficiency. They contribute to green building certifications such as LEED (Leadership in Energy and Environmental Design) and BREEAM (Building Research Establishment Environmental Assessment Method).[9] Cultural and Architectural Significance Dapatie Skylights have been used in iconic buildings around the world, including: The Pantheon in Rome, with its famous oculus. The Louvre Pyramid in Paris, featuring a modern glass skylight design. Prism lights Prism lights are sometimes used as skylights; they redirect the light passing through.

## Solar architecture

Solar architecture means designing buildings to use the sun's heat and light to maximum advantage and minimum disadvantage, especially in the sense of harnessing solar power. 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%.
Toplighting (skylights) works well with sidelighting (windows) to maximize daylighting:
* toplighting is able to bring light into centralized areas of a building
* daylight is available throughout the day from both ambient lighting from the sky and direct exposure to the sun.
* 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.

### Materials
#### Glass

Many recent 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

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.

#### 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.

### Benefits

A study concluded that students have significantly higher test scores in classrooms that optimize daylighting, than classrooms that do not. 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.
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.