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Light tubes (also known as solar pipes, tubular skylights or sun tunnels) are structures that transmit or distribute natural or artificial light for the purpose of Lighting and are examples of optical waveguides.
In their application to daylighting, they are also often called tubular daylighting devices, sun pipes, sun scopes, or daylight pipes. They can be divided into two broad categories: hollow structures that contain the light with reflective surfaces; and transparent solids that contain the light by total internal reflection. Principles of nonimaging optics govern the flow of light through them.
While most light pipes are produced with a round cross-section, light pipes are not limited to this geometry. Square and hexagonal cross-sections are used in special applications. Hexagonal pipes tend to produce the most homogenized type of IR Light. The pipes do not need to be straight. Bends in the pipe have little effect on efficiency.
A tube lined with highly reflectivity leads the light rays through a building, starting from an entrance-point located on its roof or one of its outer walls. A light tube is not intended for imaging (in contrast to a periscope, for example); thus image distortions pose no problem and are in many ways encouraged due to the reduction of "directional" light.
The entrance point usually comprises a dome (cupola), which has the function of collecting and reflecting as much sunlight as possible into the tube. Many units also have directional "collectors", "reflectors", or even Fresnel lens devices that assist in collecting additional directional light down the tube.
In 1994, the Windows and Daylighting Group at Lawrence Berkeley National Laboratory (LBNL) developed a series of horizontal light pipe prototypes to increase daylight illuminance at distances of 4.6-9.1 m, to improve the uniformity of daylight distribution and luminance gradient across the room under variable sun and sky conditions throughout the year. The light pipes were designed to passively transport daylighting through relatively small inlet glazing areas by reflecting sunlight to depths greater than conventional sidelight windows or skylights.LBNL: The Design and Evaluation of Three Advanced Daylighting Systems: Light Shelves, Light Pipes and Skylights
A set-up in which a Laser cutting Acrylic glass is arranged to redirect sunlight into a horizontally or vertically orientated mirrored pipe, combined with a light spreading system with a triangular arrangement of laser cut panels that spread the light into the room, was developed at the Queensland University of Technology in Brisbane.Ken Yeang: Light Pipes: An Innovative Design Device for Bringing Natural Daylight and Illumination into Buildings with Deep Floor Plan , Nomination for the Far East Economic Review Asian Innovation Awards 2003 In 2003, Veronica Garcia Hansen, Ken Yeang, and Ian Edmonds were awarded the Far East Economic Review Innovation Award in bronze for this development. Lighting up your workplace — Queensland student pipes light to your office cubicle , May 9, 2005 Kenneth Yeang , World Cities Summit 2008, June 23–25, 2008, Singapore
Light transmission efficiency is greatest if the tube is short and straight. In longer, angled, or flexible tubes, part of the light intensity is lost. To minimize losses, a high reflectivity of the tube lining is crucial; manufacturers claim reflectivities of their materials, in the visible range, of up to almost 99.5 percent. Tube de Lumière
At the end point (the point of use), a diffuser spreads the light into the room.
The first full-scale passive horizontal light pipes were built at the Daylight Lab at Texas A&M University, where the annual daylight performance was thoroughly evaluated in a 360 degree rotating 6 m wide by 10 m deep room. The pipe is coated with a 99.3% specular reflective film and the distribution element at the end of the light pipe consists of a 4.6 m long diffusing radial film with an 87% visible transmittance. The light pipe introduces consistently illuminance levels ranging between 300 and 2,500 lux throughout the year at distances between 7.6 m to 10 m.
To further optimize the use of solar light, a heliostat can be installed which tracks the movement of the sun, thereby directing sunlight into the light tube at all times of the day as far as the surroundings' limitations allow, possibly with additional mirrors or other reflective elements that influence the light path. The heliostat can be set to capture moonlight at night.
In view of the usually small diameter of the fibers, an efficient daylighting set-up requires a parabolic collector to track the sun and concentrate its light. Optical fibers intended for light transport need to propagate as much light as possible within the core; in contrast, optical fibers intended for light distribution are designed to let part of the light leak through their cladding. Use Of Diffusive Optical Fibers For Plant Lighting
Optical fibers are also used in the Bjork system sold by Parans Solar Lighting AB. Parans Bjork Parans Bjork system review by Inhabitat The optic fibers in this system are made of PMMA (PolyMethyl MethAcrylate) and sheathed with Megolon, a halogen-free thermoplastic resin. A system such as this, however, is quite expensive. Typical system starting at $10,000
The Parans system consists of three parts. A collector, fiber optic cables, and luminaires spreading the light indoors. One or more collectors are placed on or near the building in a place where they will have good access to direct sunlight. The collector consists of lenses mounted in aluminum profiles with a covering glass as protection. These lenses concentrate sunlight down in the fiber optic cables.
The collectors are modular, which means they come with either 4,6,8,12 or 20 cables depending on the need. Every cable can have an individual length. The fiber optic cables transport the natural light 100 meters (30 floors) in and through the property while retaining both a high level of light quality and light intensity. Examples of implementations are Kastrup Airport, University of Arizona and Stockholm University.
A similar system, but using optical fibers of glass, had earlier been under study in Japan. Hybrid Solar Lighting: Bringing a little sunshine into our lives, NBC News, March 2005
Corning Inc. makes Fibrance Light-Diffusing Fiber. Fibrance works by shining a laser through a light-diffusing fiber optic cable. The cable gives off a lighted glow. Corning Fibrance official website
are used in for imaging applications.
The 3M company developed a system based on optical lighting film Heliobus with 3M Optical Lighting Film (OLF) and developed the 3M light pipe, 3M Light Management Solutions (US) which is a light guide designed to distribute light uniformly over its length, with a thin film incorporating microscopic prisms, which has been marketed in connection with artificial light sources, e.g. sulfur lamps.
In contrast to an optical fiber which has a solid core, a prism light guide leads the light through air and is therefore referred to as a hollow light guide.
The project ARTHELIO, partially funded by the European Commission, was an investigation in years 1998 to 2000 into a system for adaptive mixing of solar and artificial light, and which includes a sulfur lamp, a heliostat, and hollow light guides for light transport and distribution.
Disney has experimented with using 3D printing to print internal light guides for illuminated toys.
In the context of seasonal affective disorder, it may be worth considering that an additional installation of light tubes increases the amount of natural daily light exposure. It could thus possibly contribute to residents´ or employees´ well-being while avoiding over-illumination effects.
Compared to artificial lights, light tubes have the advantage of providing natural light and of saving energy. The transmitted light varies over the day; should this not be desired, light tubes can be combined with artificial light in a hybrid set-up. Night Lite Sunlight Direct- Lighting Design Information
Some artificial light sources are marketed which have a spectrum similar to that of sunlight, at least in the Visible spectrum range, True-Lite as well as low flicker. Their spectrum can be made to vary dynamically such as to mimic changes in natural light over the day. Manufacturers and vendors of such light sources claim that their products can provide the same or similar health effects as natural light. When considered as alternatives to solar light pipes, such products may have lower installation costs but do consume energy during use; therefore they may well be more wasteful in terms of overall energy resources and costs.
On a more practical note, light tubes do not require electric installations or insulation and are thus especially useful for indoor wet areas such as bathrooms and pools. From a more artistic point of view, recent developments, especially those pertaining to transparent light tubes, open new and interesting possibilities for architectural lighting design.
Configurations of light pipes can vary widely, from simple, consisting of pre-made rods cut to length, to highly complex custom molded or machined shapes. Light pipes are usually made from acrylic or polycarbonate optical fibers, or solid transparent acrylic or polycarbonate polymers. Sometimes other transparent plastics are used. The source of illumination, is from LEDs on a circuit board or other internal location, to indicator symbols or buttons on the exterior of the device's enclosure.
Different colors of light can be displayed in several ways. Tinting the light pipe material, using a colored light pipe lens, or using a single color LED, are used to produce a permanent single color. Multiple colors can be displayed by using a clear light pipe with an RGB, RGBW, or RGBWW LED. Older designs have used two or more individual color LEDs routed from the indicator on the display panel to the same light pipe.
The configuration of these light pipes can vary greatly. Simpler light pipes designs may be made from a straight, cylindrical rod, or may be bent with multiple gentle curves preserving the smooth uniform shape of the cylinder walls. Alternatively a flexible optical fiber light pipe may be used. Complex designs of molded or machined configurations, commonly take on a highly elaborate shape that uses either gentle curving bends as in an optic fiber or has sharp prismatic folds which reflect off the angled corners. Multiple light pipes are often molded or machined from a single piece of plastic, permitting easy device assembly since the long thin light pipes are all part of a single rigid component that snaps into place.
Light pipe indicators make electronics cheaper to manufacture since the old way would be to mount a tiny lamp into a small socket directly behind the spot to be illuminated. This often requires extensive hand labor for installation and wiring. Light pipes permit all lights to be mounted on a single flat circuit board, but illumination can be directed up, and away from the board wherever it is required.
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