page_title: Skylight
section_title: Description
hierarchical_section_title: Skylight / Description
caption_attribution_description: English: Liverpool Central Library
context_page_description: A skylight is a light-transmitting structure that forms all or part of the roof space of a building for daylighting purposes.
context_section_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
  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). 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.
  Prism lights
  Prism lights are sometimes used as skylights; they redirect the light passing through.
caption: TDD skylight on the roof terrace of Liverpool Central Library
exif: {"Image ImageDescription": "", "Image Make": "SONY", "Image Model": "DSC-W690", "Image Orientation": "Horizontal (normal)", "Image XResolution": "350", "Image YResolution": "350", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2016:09:18 16:58:08", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "274", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 51, 48, 48, 0, 0, 0, 2, 0, 2, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail Make": "SONY", "Thumbnail Model": "DSC-W690", "Thumbnail Orientation": "Horizontal (normal)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail DateTime": "2016:09:18 16:58:08", "Thumbnail JPEGInterchangeFormat": "11192", "Thumbnail JPEGInterchangeFormatLength": "7239", "EXIF ExposureTime": "1/100", "EXIF FNumber": "8", "EXIF ExposureProgram": "Landscape Mode", "EXIF ISOSpeedRatings": "80", "EXIF ExifVersion": "0230", "EXIF DateTimeOriginal": "2016:09:18 16:58:08", "EXIF DateTimeDigitized": "2016:09:18 16:58:08", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "4", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "441/128", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "89/20", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2592", "EXIF ExifImageLength": "1944", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "10968", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Landscape", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal"}