Knowledge Centre – Passive Strategies

Light Emitting Diodes (LEDs)

Light emitting diodes is a solid state lighting system based on p-n junction semiconductor crystal where photons are generated through radiative recombination through charge carriers (electrons and holes). The system is in line with semiconductor diode which is formed by combining p- and n-type materials together to form a junction. The combination forms a layer of ionized acceptors in the p-side and another layer of ionized donors in the n-side forming a potential junction. With electric current across the junction, the electrons will get energized to jump from the one layer and recombine with the holes emitting a photon. Average life time expectancy of LED is 15,000 to 25,000 hours with a CRI ranging from 50 – 90. Such a wide range of life expectancy and CRI is because the product is in a nascent stage of its development and no standards are available in the market for a uniform manufacturing.

Key advantages:

  • Small in size and robust in design
  • Long life time expectancy
  • No toxic content and easy to recycle
  • Has short start and re-starting time
  • High luminous efficacy
  • Low heat load

Key disadvantages:

  • High price
  • Low luminous flux
  • Risk of glare
  • No standards are available for product manufacturing
  Luminous efficacy Lamp life (Hours) Control integration Re-strike time CRI Price of product Cost to operate
Incandescent 5 – 15 700 – 1000 Good Prompt Good Low Very high
Tungsten Halogen 10 – 35 1000 – 2500 Good Prompt Very good Low High
Mercury Vapour 30 – 45 4000 – 6000 Not possible 2-5 mins Average Average Average
CFL 45 – 70 6000 – 8000 With few lamps Prompt Very good Low Low
Fluorescent lamps (T12 and T8) 40 – 60 5000 – 8000 Good 2-5 mins Good Low High
Fluorescent lamps (T5) 60 – 90 10000 – 18000 Good Prompt Good High Low
Metal Halide 50 – 100 6000 – 10000 Not possible 5 – 10 mins Good High Low
High pressure sodium 40 – 90 6000 – 12000 Not possible 2- 5 mins Good, depending on product High Low
LEDs 90 – 120 20000 – 30000 Good Prompt Good High Low