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Promoptica “Nouvelles Techniques d’Eclairage”

Promoptica “Nouvelles Techniques d’Eclairage” Inorganic LEDs: working principles and prospects for general lighting applications Laboratory for Light and Lighting KaHo St.-Lieven University College Gent (B) P. Hanselaer. Liège Novembre 8, 2007. 1. Main categories of light sources.

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Promoptica “Nouvelles Techniques d’Eclairage”

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  1. Promoptica “Nouvelles Techniques d’Eclairage” Inorganic LEDs: working principles and prospects for general lighting applications Laboratory for Light and Lighting KaHo St.-Lieven University College Gent (B) P. Hanselaer Liège Novembre 8, 2007

  2. 1. Main categories of light sources Laboratorium voor Lichttechnologie

  3. Light sources Incandescent Discharge Solid State LED Sodium Mercury High pressure Low pressure Low pressure High pressure Outdoor illumination Outdoor, Shops Metalhalide FL, CFL Laboratorium voor Lichttechnologie

  4. 2. Elementary Solid State Physics Laboratorium voor Lichttechnologie

  5. E Bandgap Eg Intrinsic semiconductor Conduction band Valence band “Free” electrons and holes Laboratorium voor Lichttechnologie

  6. E Band gap Eg Recombination between an electron and a hole: energy can be released by the creation of a photon Photon Light! At room temperature: only a small amount of free electrons and holes: limited number of photons! Laboratorium voor Lichttechnologie

  7. E Extrinsic semiconductor (n) Donor-atoms (P); n-type Laboratorium voor Lichttechnologie

  8. E Extrinsic semiconductor (p) Acceptor-atoms (B); p-type Laboratorium voor Lichttechnologie

  9. Injection of free electrons in p-type and free holes in n-typep-n junction! p n + - Laboratorium voor Lichttechnologie

  10. 3. Electrical characteristics Laboratorium voor Lichttechnologie

  11. Electrical characteristics • Diode characteristic • Low, dc voltage • Forward voltage dependent on bandgap of the semiconductor: • AlGaInP: 2.95 V typ. • InGaN: 3.42 V typ. Laboratorium voor Lichttechnologie

  12. Electrical characteristics Laboratorium voor Lichttechnologie

  13. 4. Optical characteristics Laboratorium voor Lichttechnologie

  14. Optical characteristics: spectrum Photon energy (and colour) is determined by bandgap Eg Rather monochromatic radiation Laboratorium voor Lichttechnologie

  15. Optical characteristics: spectrum Peak wavelength λp : from UV to IR Full Width at Half Maximum: from 20 to 50 nm Laboratorium voor Lichttechnologie

  16. Optical characteristics: chromaticity • Purity • Dominant wavelength CIE chromaticity Laboratorium voor Lichttechnologie

  17. Optical characteristics: chromaticity Additive mixing with wide colour gamut CIE chromaticity Laboratorium voor Lichttechnologie

  18. Optical characteristics: colour Bandgap engineering to obtain an extensive range of wavelengths and colours:use of compound semiconductors Laboratorium voor Lichttechnologie

  19. Compound Semiconductors Laboratorium voor Lichttechnologie

  20. InGaN AlGaInP Laboratorium voor Lichttechnologie

  21. Optical characteristics: white LEDs Laboratorium voor Lichttechnologie

  22. Three or more LEDs of different Colors +The more colours one has to mix, the more control one has in producing white light with a high color rendering index. + Photons from each LED contribute directly to the light intensity, i.e. no conversion efficiencies have to be considered. + Extensive range of hue’s can be obtained - Optical control, coloured shadows Laboratorium voor Lichttechnologie

  23. Osram 6 lead multiLED Laboratorium voor Lichttechnologie

  24. Optical characteristics:Radiant/luminous Flux Φ(e) luminous flux # photons # recombinations forward electrical current Laboratorium voor Lichttechnologie

  25. LED’s: current driven Laboratorium voor Lichttechnologie

  26. Optical characteristics: efficacy Efficacy red: 55 lm/W (room temperature)Energy-efficiency: 24 %LossesNon-radiative recombination (heat)Internal reflections Laboratorium voor Lichttechnologie

  27. Non-radiative recombination Temperature of the semiconductor junction increases! Laboratorium voor Lichttechnologie

  28. Active material Substrate Total Internal Reflection Partially reflected Totally reflected absorption Laboratorium voor Lichttechnologie

  29. Internal reflections1. semiconductor-encapsulant2. encapsulant-air Laboratorium voor Lichttechnologie

  30. Optical characteristics: spatial www.nichia.com • Dependent on • position of die and reflector • shape of the external dome Laboratorium voor Lichttechnologie

  31. Optical characteristics: spatial Secundary optics Laboratorium voor Lichttechnologie

  32. 5. Effect of Temperature Laboratorium voor Lichttechnologie

  33. Effect of Temperature: luminous flux Increase of non-radiative recombination! Laboratorium voor Lichttechnologie

  34. Effect of Temperature: peak wavelength and light flux Decrease of the bandgap, increase of wavelength! Laboratorium voor Lichttechnologie

  35. Effect of temperature: chromaticity Chromaticity versus warm-up time Laboratorium voor Lichttechnologie

  36. Effect of temperature: lumen maintenance http://www.lrc.rpi.edu/programs/solidstate/ongoingProjects.asp?ID=57 Laboratorium voor Lichttechnologie

  37. Thermal management Laboratorium voor Lichttechnologie

  38. Thermal management 10 °C/W Laboratorium voor Lichttechnologie

  39. Determination of junction temperature Laboratorium voor Lichttechnologie

  40. 6. Photometry of LEDsPhotometer/colorimeter or spectroradiometer Laboratorium voor Lichttechnologie

  41. Photometer Laboratorium voor Lichttechnologie

  42. Important errors in tails of eye sensitivity curve Laboratorium voor Lichttechnologie

  43. Spectroradiometer Bandwidth: 5 nm Laboratorium voor Lichttechnologie

  44. Photometry of LEDs: intensity • Some LEDs have a very narrow radiation pattern (FWHM 2°) • Large distance to detector and small detector aperture required. • CIE 127 standardisation: “averaged LED intensity” at 316 mm (A) or 100 mm (B) distance and 1 cm2 detector area. Laboratorium voor Lichttechnologie

  45. Photometry of LEDs: luminous fluxReference light source required Laboratorium voor Lichttechnologie

  46. Fast measurements: partial flux Laboratorium voor Lichttechnologie

  47. 7. LED penetration into general lighting Laboratorium voor Lichttechnologie

  48. LED penetration into General Lighting: main obstacles • Luminous flux • Efficacy • Colour and flux maintenance • Thermal management • Reproducibility • Price Laboratorium voor Lichttechnologie

  49. LED penetration into General Lighting: obstacles : luminous flux (white) Laboratorium voor Lichttechnologie

  50. LED penetration into General Lighting: obstacles : luminous flux Luxeon Laboratorium voor Lichttechnologie

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