Light tube

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This article is about "light tubes" used for the illumination of buildings. For other uses of the phrase "light tubes", see Light tube (disambiguation).

Light tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also called solar tubes, solar pipes, daylight pipes, or solar light pipes.

Generally speaking, a light pipe or light tube may refer to:

  • a tube or pipe for transport of light to another location, minimizing the loss of light;
  • a transparent tube or pipe for distribution of light over its length, either for equidistribution along the entire length (see also sulfur lamp) or for controlled light leakage.

Both have the purpose of lighting, for example in Architecture.

Contents

[edit] Materials and set-up

[edit] Light tube with reflective material

A light tube installed in the subterranean train station at Potsdamer Platz, Berlin, seen from above ...
A light tube installed in the subterranean train station at Potsdamer Platz, Berlin, seen from above ...
... and below ground. (More images on Wikimedia Commons)
... and below ground.
(More images on Wikimedia Commons)

Also known as a "tubular skylight", this is the oldest and most widespread type of light tube used for daylighting.

A round tube lined with highly reflective material 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.

The entrance point usually comprises a dome (cupula), or alternatively a diamond-shaped light collector, which has the function of collecting and reflecting as much sunlight as possible into the tube.

Light transmssion 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 98 to almost 99.5 percent.[1][2][3]

At the end point (the point of use), a diffuser spreads the light into the room.[4][5]

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.

[edit] Optical fiber

Optical fibers are well known as fiberscopes for imaging applications and as light guides for a wide range of non-imaging applications. In the latter context, they can also be used for daylighting: a solar lighting system based on plastic optical fibers was in development at Oak Ridge National Laboratory in 2004;[6][7] the system was installed at the American Museum of Science and Energy, Tennessee, USA, in 2005,[8] and brought to market the same year by the company Sunlight Direct.[9][10]

A similar system, but using optical fibers of glass, had earlier been under study in Japan.[11]

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.[12]

[edit] Transparent hollow light guides

A prism light guide was developed in 1981[13] and has been used in solar lighting for both transport and distribution of light.[14][15] A large solar pipe based on the same principle has been set up in a narrow courtyard of a 14-floor building of a Washington D.C. law firm in 2001,[16][17][18][19][20] and a similar proposal has been made for London.[21] A further system has been installed in Berlin&nbsp.[22]

The 3M company developed a system based on optical lighting film[23] and developed the 3M light pipe,[24] which is a light guide designed to distribute light uniformly over its length, with a thin film incorporating microscopic prisms,[25] 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 hollow light guide.

The project ARTHELIO,[26][27] 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.

[edit] Fluorescence based system

In a system developed by Fluorosolar and the University of Technology, Sydney, two fluorescent polymer layers in a flat panel capture short wave sunlight, particularly ultraviolet light, generating red and green light, respectively, which is guided into the interior of a building. There, the red and green light is mixed with artificial blue light to yield white light, without infrared or ultraviolet. This system, which collects light without requiring mobile parts such as a heliostat or a parabolic collector, is intended to transfer light to any place within a building. [28][29][30] By capturing ultraviolet the system can be especially effective on bright but overcast days; this since ultraviolet is diminished less by cloud cover than are the visible components of sunlight.

[edit] Properties and applications

[edit] Solar and hybrid lighting systems

Solar light pipes, compared to conventional skylights and other windows, offer better heat insulation properties and more flexibility for use in inner rooms, but less visual contact with the external environment.

In the context of seasonal affective disorder, it may be worth consideration 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, it can be combined with artificial light in a "hybrid" set-up.[31][32][33][34]

Some artificial light sources are marketed which have a spectrum similar to that of sunlight, at least in the human visible spectrum range,[35][36][37] as well as low flicker.[38][39] In some cases, their spectrum varies dynamically such as to mimick the changes of natural light over the day.[40] Manufacturers and vendors of such light sources claim that their products can provide the same or similar health effects as natural light.[41][42][43] 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 over-all 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 design.

[edit] References

  1. ^ http://www.solarspot.it/images/depliant_inglese_2006.pdf#page=5
  2. ^ (German) http://www.alanod.de/opencms/sites/alanod.de/de/miro/MIRO_Produkte/MIRO_LIGHTPIPE/index.html
  3. ^ (French) http://www.acoram.biz/frtubelumiere.htm
  4. ^ http://www.sunpipe.com/dome.htm
  5. ^ http://www.solatube.com/res_options.php
  6. ^ http://www.ornl.gov/sci/solar/pdfs/Let%20the%20Sun%20Shine%20In.pdf Article on Hybrid Solar Lighting "Let the Sun Shine in," Discover Magazine, Vol. 25, No. 07, July 2004
  7. ^ ORNL - Solar Technologies Program
  8. ^ HSL Featured in Popular Science's What's New Section June 2005, Page 28
  9. ^ http://www.ornl.gov/info/press_releases/get_press_release.cfm?ReleaseNumber=mr20050830-00
  10. ^ http://www.sunlight-direct.com/overview.html
  11. ^ Hybrid Solar Lighting: Bringing a little sunshine into our lives ,, MSNBC, March 2005
  12. ^ http://ncr101.montana.edu/Light1994Conf/6_8_Kozai/Kozai%20Fiber%20text.htm
  13. ^ http://ncr101.montana.edu/Light1994Conf/6_6_Kneipp/Kneipp%20text.htm
  14. ^ http://www.physics.ubc.ca/ssp/research/solarlighting.htm
  15. ^ http://www.physics.ubc.ca/ssp/ssp_research.htm#lightpipe
  16. ^ http://www.detail.de/Archiv/En/HoleArtikel/5331/Artikel
  17. ^ http://www.idonline.com/adr03/solar_contemp_eco.asp
  18. ^ http://www.bomin-solar.de/Acrobat/Heliostat/H-4158-USA-Washington-SLP-2001.pdf
  19. ^ (German) http://www.bomin-solar.de/Acrobat/Press/DETAIL_4-04_SLP-Washington.pdf
  20. ^ "Solar Light Pipe in Washington, D.C.", DETAIL 4/2004, Building with light
  21. ^ http://carpenterlowings.com/clad_projects_regent%20street.htm
  22. ^ (German) "Tageslicht aus der Tube", Faktor Licht, Nr. 4, 2003 (with a description of the light pipe on Potsdamer Platz, Berlin)
  23. ^ Heliobus with 3M Optical Lighting Film (OLF)
  24. ^ http://cms.3m.com/cms/US/en/2-197/krcziFU/view.jhtml
  25. ^ http://ncr101.montana.edu/Light1994Conf/6_6_Kneipp/Kneipp%20text.htm
  26. ^ http://erg.ucd.ie/enerbuild/pdfs/ARTHELIO.pdf
  27. ^ http://www.iuav.it/Didattica1/pagine-web/facolt--di/Antonio-Ca/master-pro/Lux-Europa-2001.PDF
  28. ^ Fluorosolar
  29. ^ FluoroSolar - bringing the subshine inside, Treehugger, February 5, 2006 (retrieved on January 13, 2007)
  30. ^ Video on fluorescence based system
  31. ^ http://www.sunpipe.com/NightLite.htm
  32. ^ http://www.natural-light-skylights.com/pages/light_kit.html
  33. ^ http://www.sunlight-direct.com/lighting.html
  34. ^ http://www.physics.ubc.ca/ssp/research/solarlighting.htm
  35. ^ http://www.xternet.de/bioelektrik/en/true-lite.htm
  36. ^ http://www.solux.net/
  37. ^ (German) http://www.e-wenzl.at/lichtliteratur/vollspektrum_001.html
  38. ^ (German) http://www.e-wenzl.at/lichtliteratur/vollspektrum_001.html
  39. ^ (German) http://www.light-office.com/de/products/projects/aurasun.shtml?navid=11
  40. ^ (German) http://www.ross-licht.de/pages/fs_suno.html
  41. ^ (German) http://www.e-wenzl.at/lichtliteratur/vollspektrum_001.html
  42. ^ (German) http://www.j-lorber.de/shm/licht/vollspektrum-bedeutg.htm
  43. ^ (German) http://www.villiton.ch/vollspektrumlicht.php

[edit] External links

[edit] Overview

[edit] Other approaches to sunlight capture and transmission

[edit] See also

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