Electroluminescent Displays

1
Electroluminescent Displays

• Andy Ng

2
Introduction

• Electroluminescence first observed by Capt. Henry
  Joseph Round in 1907 in SiC.
• Commercially viable product in 1980
• Examples of EL neon lights, Timex Indiglo
• EL vs. Incandescence
• EL converts electricity directly to light
• LEDs are a type of EL

3
How EL Displays Work

• Voltage applied across phosphor
• Two conductors with phosphor in between
• Apply 100 to 200 V AC
• Transformer used to achieve voltage
• Phosphor energizes and emit a photon when
  returning to ground state
• Color depends on chemical composition and dye
  pigment

4
How EL Displays Work (cont.)

• Structure
• http//www.indiana.edu/hightech/fpd/papers/ELDs_f
  iles/image002.gif

5
How the photons are produced

• Photons produced by return of substance to ground
  state like in lasers
• Light not coherent in EL Displays
• Steps in producing photons in EL Displays
• e- reach insulator/phosphor interface in
  electronic state
• e- accelerated to high energies in large fields
  in phosphor
• e- impact or form hole e- pair that lead to
  activation of phosphor
• Photons produced when returning to ground state

6
Advantages and Disadvantages

• Low power consumption
• Large temp. range
• Does not fail abruptly (lifetime 6-8000 hours)
• Different colors
• Efficient/Low heat
• Solid state
• Thin

• Inverter (transformer) draws relatively high
  current
• Half brightness problem

7
References

• http//www.lxdinc.com/AppNotes/Backlight.htm
• http//www.howstuffworks.com/question296.htm
• http//www.byte.com/art/9506/sec9/art5.htm
• http//www.beingseen.com/faqsheets.html22
• http//www.indiana.edu/hightech/fpd/papers/ELDs.h
  tml