1. Xiaoyu Sun 24012083 2008-12-2 1

2.  Intro – what is led  How does it works  Where it uses  Advantages and disadvantages  Green city 2008-12-2 2

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

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

7. 2008-12-2 7 The holes are at lower energy level than the free electrons, so when a electron falls it loses energy.

8. 2008-12-2 8 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. 2008-12-2 9 Direct band gap Indirect band gap

10.  Indicators and signs  Lighting  Smart lighting  Non-visual applications 2008-12-2 10

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12. 2008-12-2 12 Left: A supermarket in Switzerland Right: Parking garage in Raleigh, NC

13.  Smart lighting  Non-visual applications 2008-12-2 13

14.  Dimming  Cool light  Shock resistance  Focus  Toxicity 2008-12-2 14 Efficiency Color Cost Lifetime On/Off time

15.  High price  Temperature dependence  Voltage sensitivity  Area light source 2008-12-2 15

16.  Raleigh, NC  Toronto, Canada  Ann Arbor, MI 2008-12-2 16

17.  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) 2008-12-2 17

18. CategoryTypeOverall luminous efficacy Overall luminous efficiency Incandescent5 W tungsten incandescent (120 V) 50.7% 40 W tungsten incandescent (120 V) 12.61.9% 100 W tungsten incandescent (220 V) 13.82.0% 100 W tungsten glass halogen (220 V) 16.72.4% 100 W tungsten incandescent (120 V) 16.82.5% 2.6 W tungsten glass halogen (5.2 V) 19.22.8% Light-emitting diodewhite LED10-901.5% - 13% white OLED10215% Prototype LEDsUp to 161Up to 25% 2008-12-2 18

19. ColorWavelength (nm)Voltage (V) Semi-conductor Material Infraredλ > 760ΔV < 1.9GaAs, AlGaAs Red610 < λ < 760 1.63 < ΔV < 2.03 AlGaAs, GaAsP, AlGaInP, GaP Orange590 < λ < 610 2.03 < ΔV < 2.10 GaAsP, AlGaInP, GaP Yellow570 < λ < 590 2.10 < ΔV < 2.18 GaAsP, AlGaInP, GaP Green500 < λ < 5702.18 < ΔV < 4.0 InGaN / GaN, GaP, AlGaInP, AlGaP 2008-12-2 19

20. ColorWavelength (nm)Voltage (V) Semi-conductor Material Blue450 < λ < 5002.48 < ΔV < 3.7 ZnSe, InGaN SiC/ Si as substrate Purplemultiple types2.48 < ΔV < 3.7 Blue w/red, white w/ purple Violet400 < λ < 4502.76 < ΔV < 4.0InGaN Ultravioletλ < 4003.1 < ΔV < 4.4 diamond (C), AlN, AlGaN, AlGaInN WhiteBroad spectrumΔV = 3.5 Blue/UV diode with yellow phosphor 2008-12-2 20

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23. Reference: [1] S. S. Iyer 1, 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 2008-12-2 23