R1-5 LEDs

• What does LED stand for

  Light emitting diode (an electro-chemical light source)
• How do LEDs work Electrons are released from the cathode, travel through the pn junction, and recombine with holes at the anode
• Why is it important to have a good contact between the metal leads and the semiconductor material It allows electrons to flow freely across the pn junction
• When the diode is _____, light is generated

  forward-biased
• What is a PN junction?

  a semiconductor junction which is a boundary between 2 types of semiconductor materials
• What happens in a PN junction?

  when an electron moves across the junction, it releases some energy as heat as it goes from higher energy level to lower energy level: the LED emits light when a forward current flows
• When is the LED light source considered as expired?

  Once the light output has depreciated to 50% of its initial output. Some last up to 50,000 hours
• Which light is the technology of the future?

  LEDs
• Disadvantages of LEDs?

  -currently more expensive due to high cost of manufacturing

  -very heat sensitive (negative temperature coefficient)

  -typically cast direction in one direction at a narrow angle compared to other lights (lenses needed to broaden beam)
• What are some applications of LEDs?

  -signage, decorative festive lighting, marketing displays, automotive applications

  -traffic signal lamps

  -exit signs

  -road lights

  -security lighting

  -seasonal light strings

  -task and reading lamps

  -recessed lighting

  -linear strip lighting

  -landscaping lighting

  -night lights

  -art lighting

  -stair and walkway lighting

  -pendants and overhead

  -retrofit bulbs for lamps
• LED advantages

  • Lower power consumption
  • Negligible early installation failures
  • Resistant to damage from shock and vibration: no glass or filament to break
  • Available in all colours
  • Fully dimmable
  • Cool when operating: efficiency in light without wasting heat
  • Extra low voltage devices which require fewer materials and precautions
  • They light the areas that are required to be illuminated: unwanted light does not bleed off into the environment
  • Have no moving parts, toxic gases or filament to burn. Nothing to break or pollute
  • Easily mounted in almost any location
  • Extremely long service life
  • Instant ON/OFF
  • Work well in cold temperatures
  • Have an acceptable CRI (about 70)