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Light

Light. “Light is a radiant energy able to excite the human eye and create a visual sensation” [1]. It is physically defines as a narrow wavelength-band (between 380 and 780nm ) of electromagnetic radiation visible by human eyes [2].

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Light

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  1. Light “Light is a radiant energy able to excite the human eye and create a visual sensation” [1]. It is physically defines as a narrow wavelength-band (between 380 and 780nm) of electromagnetic radiation visible by human eyes [2]. Light is thus a mix of different wavelengths that can be decomposed in several monochromatic wavelength : the colors of the rainbow. Violet (~380-450 nm) – Blue (~450-520 nm) – Green (~520-565 nm) – Yellow (~565-590 nm) - Orange (~590-625 nm) - Red (~625-780 nm) Natural light is the visible part of the solar electromagnetic radiation which arrives on the Earth. Three different kinds of radiation can be distinguish after travelling the atmosphere: ultraviolet waves (UV), visible light and infrared waves (IR). It is important, in architecture, to take into account these two other types of invisible radiations because they can entertain overheating (IR) and discoloration (UV). [1] IESNA Lighting Handbook, Illuminating Engineering Society of North America, 2000 [2] Introduction to Architectural Science: The Basis of Sustainable Design, S. Szokolay, Architectural Press, 2003 Architecture & Climat, UCL

  2. Light Since the 17th century, two rival theories about the nature of light have existed. Isaac Newton argued that light must be a stream of particles, while Christian Huygens thought that it must be propagating like a wave. In 1905, Albert Einstein reconciled the theory of Huygens with that of Newton in explaining the photoelectric effect. Einstein proves that light does not act as a wave in introducing the existence of photons, quanta of luminous energy which have some qualities of particles. Einstein postulated that the frequency (ν) of this light, is related to the energy E of the photons: E = hν, where h is the Planck's constant (6,626*10-34Js). An easy way to highlight the wave-particle duality isthe double-slit experiment of Young. This experiment firstly showed, during the XIXth century, the undulatory aspect of light. But, slightly modified, it can also show the wave-particle duality of light. In this experiment, a screen pierced by two thin, parallel and closed slits is lit by a source of light. A photographic paper is placed behind this screen. When travelling the two slits, the initial source of light is divided in two secondary sources. And when light reaches the photographic paper, rays of light can be observed, which are typical of the wave aspect of light. If the intensity of the light source is reduced, the collision of each photon with the photographic paper can be clearly observed. Finally, after a time, the interference pattern appears. So the wave-particle duality is observed. Nowadays, some properties of light can be explained with the particle theory (reflection, …), and others with the wave theory (diffraction, polarization, …). http://fr.wikipedia.org/wiki/Dualit%C3%A9_onde-particule http://new-learn.info/learn/packages/synthlight/handbook/index.html http://fr.wikipedia.org/wiki/Dualit%C3%A9_onde-particule

  3. Light Anti UV and anti IR protections When choosing a type of glazing, architect should take into account the entirety of solar radiation. Three kinds of waves can be distinguish in natural light : UV, visible light and IR. Ultraviolet will be a cause of discoloration of objects while infrared will entertain overheating. Anti UV films are a way to protect objects from the discoloration due to the sun (in museum, shops, …). Anti IR films and low emissivity glazing will be a way to reject heat from the sun and avoid overheating. Selectivity index Selectivity index of glazing is the ratio between the luminous transmission of the glazing (TL) and its solar factor (g). This index informs about the efficacy of glazing. TL is generally expected to be high while g to be low. A selectivity index of 2 corresponds to the physical limit. An efficient glazing has selectivity index close to 2.

  4. Light To teach students about physics of light, teachers can notice that: Sun rays are hot because sun is more than visible light: it contains also infrared light; Tanning is a natural response to exposure to sunlight and ultraviolet waves; Human eye needs light to perceive the world. To learn more about physics of light: - The Illuminating Engineering Society of North America, The IESNA Lighting Handbook: Reference and Application, Ninth Edition, 2000. !! New edition available on January 2010!! - Axel Jacobs, Marc Fontoynont, ArisTsangrassoulis, AfroditiSynnefa, Wilfried Pohl, and Andreas Zimmermann. SynthLight Handbook, 2002. Available for free on http://www.learn.londonmet.ac.uk/packages/synthlight/index.html. - Steven V. Szokolay, Introduction to architectural Science: the basis of sustainable design, 2nd edition, 2008.

  5. Light To learn more about physics of light, visit the websites: http://acejizhang.tripod.com/Quantum/twoslit_experiment.html (two-slit experiment of Young) http://hyperphysics.phy-astr.gsu.edu/hbase/ligcon.html#c1

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