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MODULE 4: LEDs SUMMER CHALLENGE Electrical Engineering: Smart Lighting

MODULE 4: LEDs SUMMER CHALLENGE Electrical Engineering: Smart Lighting. Michael Rahaim, PhD Candidate Multimedia Communications Lab Boston University mrahaim@bu.edu. Overview. From “Lighting” to Smart Lighting What is a Diode? LEDs! Electrical Power LED Drivers.

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MODULE 4: LEDs SUMMER CHALLENGE Electrical Engineering: Smart Lighting

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  1. MODULE 4: LEDsSUMMER CHALLENGEElectrical Engineering: Smart Lighting Michael Rahaim, PhD Candidate Multimedia Communications Lab Boston University mrahaim@bu.edu

  2. Overview • From “Lighting” to Smart Lighting • What is a Diode? • LEDs! • Electrical Power • LED Drivers

  3. Lighting & Color Science • Visible Light is a form of electromagnetic radiation • The human eye responds to the visible light spectrum • White light is the presence of all colors mm Wave Spectrum 100km 10km 1km 100m 10m 1m 100mm 10mm 1mm 100μm 10μm 1μm 100nm 10nm 1nm 3kHz 30kHz 300kHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz 3THz 30THz 300THz 3PHz 30PHz 300PHz microwave Spectrum 400nm 780nm Visible Light Spectrum 750THz 380THz

  4. Smart Lighting • In what ways can light be better? • Energy Efficiency • Healthy Lighting • Productivity (Data access)

  5. What is a diode? • A device that allows current to flow in one direction • Forward Bias Voltage • For current to flow, diodes require a forward bias voltage • In an ideal diode, voltage drop remains constant Anode Cathode

  6. Kirchhoff’s Voltage Law • The algebraic sum of all voltages in a loop must equal 0 • Relationship to Diode circuits • Once the diode reaches the turn on voltage, increases with • Current through the circuit increases with • Decreasing also increases with + - + - - +

  7. LEDs David Miller

  8. How Do LEDs Work? • LED Materials • Semiconducting materials • Current can only flow in one direction • Passing through the LED, electrons lose energy • Lost energy creates photons • Photons have discrete wavelength related to band-gap • Band-gap width and energy • The wider the band-gap, the greater the energy of the photon released • Specialized materials & processes required to achieve wide band-gap • Planck’s Relation:

  9. How Do LEDs Work? Materials Science Quantum Physics Physiology, Neuroscience Enineering Design Process

  10. Small Band Gap: Low Energy Red Light e- e- Conduction Band Small Band Gap Valence Band

  11. Large Band Gap: High Energy Blue Light e- e- Conduction Band Large Band Gap Valence Band

  12. A (Brief) History of LEDs

  13. LED Applications: Signals and Indicators

  14. LED Applications: Lighting & Illumination

  15. LED Applications: Sensing, Control, Moving Data

  16. LED Applications: Other

  17. Experiment I • LED circuit • Determining the turn-on voltage

  18. Electrical Power • Power is the rate that energy is consumed. • Power is measured in Watts [] or [J/s] • Energy sources (such as batteries) produce power while the load of the circuit absorbs power. This is another one of those important equations… + - + - - +

  19. Electric Power • Combining the previous equation with OHMS LAW: • Consider a incandescent attached to a source • How does current change if you replace the 60W bulb with 120W bulb?

  20. Experiment II • LED Drivers • Power Consumption

  21. Recap • What did you today?

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