Towards the ideal white LED light source

94 Pages·2015·5.11 MB·English

Towards the ideal
white LED light source

Youri Meuret
The Light & Lighting Laboratory
Optical
Lighting
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Towards the ideal white LED light source
for general lighting applications
The ideal white light source for lighting?
Specification/properties Ideal
- Ef ficacy - ≈ 400 lumen/watt
- Sp ectrum - CRI = 100
- Li fetime, stability, robustness - 100 khours at this moment
- Co st - low cost per lumen x hours
- Fo rmfactor - Application depending
- To tal light output - Application depending
- Ra diation pattern - Application depending
- Lu minance
- Application depending
Overview
• LED fundamentals
• LED efficiency
• Three key issues of LED technology
• Efficient white LED light + state-of-the-art
• LED luminance
• LED alternatives
LED fundamentals
From a very simple
solid-state physics
point of view
Conduction in intrinsic semiconductors
E
Conduction band
Bandgap E
g
Valence band
The recombination of a free electron and a hole
can lead to the emission of a photon
E
Band gap E
g
For an intrinsic semiconductor at room temperature, the amount of
free electrons and holes is low → the chance that these meet is low
→ the amount of created photons is low.
c
E  Ephoton  h.f  h.

n-type p-type
semiconductor semiconductor
+ -
+ -
Bandgap → the smallest frequency
F. Schubert “Light-Emitting Diodes” Cambridge University Press (2006)