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Introduction of Light-Emitting Diode

Introduction of Light-Emitting Diode. Xiaoyu Sun 24012083. Light-emitting Diode. Intro – what is led How does it works Where it uses Advantages and disadvantages Green city. What is LED. Photo from www.mulelighting.com. Photo from www.gizmowatch.com.

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Introduction of Light-Emitting Diode

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  1. Introduction of Light-Emitting Diode Xiaoyu Sun 24012083

  2. Light-emitting Diode • Intro – what is led • How does it works • Where it uses • Advantages and disadvantages • Green city

  3. What is LED Photo from www.mulelighting.com Photo from www.gizmowatch.com Photo Credit - sandstep via Flickr

  4. Structure

  5. Inner workings

  6. How it works When current flows across a diode, negative electrons move one way and positive holes move the other way.

  7. How it works (cont’d) The holes are at lower energy level than the free electrons, so when a electron falls it loses energy.

  8. How it works (cont’d) The energy is emitted in the form of a light photon. The wavelength depends on the band gap energy of the materials forming the p-n junction.

  9. Direct bandgap vs. Indirect bandgap Direct band gap Indirect band gap

  10. Where it works • Indicators and signs • Lighting • Smart lighting • Non-visual applications

  11. Indicators and signs

  12. Lighting Left: A supermarket in Switzerland Right: Parking garage in Raleigh, NC

  13. Other applications • Smart lighting • Non-visual applications

  14. Advantages • Dimming • Cool light • Shock resistance • Focus • Toxicity • Efficiency • Color • Cost • Lifetime • On/Off time

  15. Why bulbs haven’t been replaced • High price • Temperature dependence • Voltage sensitivity • Area light source

  16. Green cities • Raleigh, NC • Toronto, Canada • Ann Arbor, MI

  17. Efficiency • Roughly estimation: Assume φ = 45 lm I = 350 mA V = 3.42 V luminous efficacy 45 lm/(0.35 A x 3.42 V) = 38 lm/W (From the website of U.S. department of energy)

  18. Efficiency (cont’d)

  19. Colors vs. Materials

  20. Colors vs. Materials (cont’d)

  21. Cost Saving

  22. Lifetime

  23. Reference: [1] S. S. Iyer1, Y. -H. Xie. Science 2 April 1993: Vol. 260. no. 5104, pp. 40 – 46. Light Emission from Silicon [2] Nobuyoshi Koshida, Hideki Koyama. Efficient Visible Photoluminescence from Porous Silicon. [3] http://en.wikipedia.org [4] http://electronics.howstuffworks.com

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