Promoptica

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• Promoptica
• Nouvelles Techniques dEclairage
• Inorganic LEDs working principles and prospects
  for general lighting applications
• Laboratory for
• Light and Lighting
• KaHo St.-Lieven
• University College
• Gent (B)
• P. Hanselaer

Liège Novembre 8, 2007
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1. Main categories of light sources
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Light sources
Discharge
Incandescent
Solid State
LED
Sodium
Mercury
High pressure
Low pressure
Low pressure
High pressure
Outdoor illumination
Outdoor, Shops
Metalhalide
FL, CFL
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2. Elementary Solid State Physics
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Intrinsic semiconductor
Conduction band
Valence band
Free electrons and holes
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Recombination between an electron and a hole
energy can be released by the creation of a photon
Photon
Light!
At room temperature only a small amount of free
electrons and holes limited number of photons!
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Extrinsic semiconductor (n)
Donor-atoms (P) n-type
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Extrinsic semiconductor (p)
Acceptor-atoms (B) p-type
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Injection of free electrons in p-type and free
holes in n-typep-n junction!
p
n

-
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3. Electrical characteristics
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Electrical characteristics

• Diode characteristic
• Low, dc voltage
• Forward voltage dependent on bandgap of the
  semiconductor
• AlGaInP 2.95 V typ.
• InGaN 3.42 V typ.

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Electrical characteristics
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4. Optical characteristics
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Photon energy (and colour) is determined by
bandgap Eg
Optical characteristics spectrum
Rather monochromatic radiation
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Optical characteristics spectrum
Peak wavelength ?p from UV to IR Full Width at
Half Maximum from 20 to 50 nm
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Optical characteristics chromaticity

• Purity
• Dominant wavelength

CIE chromaticity
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Optical characteristics chromaticity
Additive mixing with wide colour gamut
CIE chromaticity
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Bandgap engineering to obtain an extensive range
of wavelengths and coloursuse of compound
semiconductors
Optical characteristics colour
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Compound Semiconductors
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InGaN
AlGaInP
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Optical characteristics white LEDs
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Three or more LEDs of different Colors

• The more colours one has to mix, the more
  control one has in producing white light with a
  high color rendering index.
• Photons from each LED contribute directly to
  the light intensity, i.e. no conversion
  efficiencies have to be considered.
• Extensive range of hues can be obtained
• - Optical control, coloured shadows

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Osram 6 lead multiLED
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Optical characteristicsRadiant/luminous Flux
F(e)
luminous flux
photons
recombinations
forward electrical current
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LEDs current driven
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Optical characteristics efficacy
Efficacy red 55 lm/W (room temperature)Energy
-efficiency 24 LossesNon-radiative
recombination (heat)Internal reflections
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Non-radiative recombination
Temperature of the semiconductor junction
increases!
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Total Internal Reflection
Partially reflected
Totally reflected
absorption
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Internal reflections1. semiconductor-encapsulan
t2. encapsulant-air
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Optical characteristics spatial
www.nichia.com

• Dependent on
• position of die and reflector
• shape of the external dome

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Secundary optics
Optical characteristics spatial
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5. Effect of Temperature
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Effect of Temperature luminous flux
Increase of non-radiative recombination!
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Effect of Temperature peak wavelength and light
flux
Decrease of the bandgap, increase of wavelength!
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Effect of temperature chromaticity
Chromaticity versus warm-up time
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Effect of temperature lumen maintenance
http//www.lrc.rpi.edu/programs/solidstate/ongoing
Projects.asp?ID57
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Thermal management
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Thermal management
10 C/W
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Determination of junction temperature
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6. Photometry of LEDsPhotometer/colorimeter or
spectroradiometer
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Photometer
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Important errors in tails of eye sensitivity
curve
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Spectroradiometer
Bandwidth 5 nm
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Photometry of LEDs intensity

• Some LEDs have a very narrow radiation pattern
  (FWHM 2)
• Large distance to detector and small detector
  aperture required.
• CIE 127 standardisation averaged LED
  intensity at 316 mm (A) or 100 mm (B) distance
  and 1 cm2 detector area.

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Photometry of LEDs luminous fluxReference light
source required
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Fast measurements partial flux
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7. LED penetration into general lighting
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LED penetration into General Lighting main
obstacles

• Luminous flux
• Efficacy
• Colour and flux maintenance
• Thermal management
• Reproducibility
• Price

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LED penetration into General Lighting obstacles
luminous flux (white)
P(W) I(mA) F(lm)
0.070 20 1.5
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LED penetration into General Lighting obstacles
luminous flux
P(W) I(mA) F(lm)
1.2 350 60
3.6 1000 100
5.0 700 120
Luxeon
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LED penetration into General Lighting obstacles
luminous flux
P(W) I(mA) F(lm)
4.7 420 108
26 2300 567
860 13300
Chip on board technology Lamina Ceramics, Osram
Multiple LED package
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LED penetration into General Lighting obstacles
efficacy/ CRI
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CRI (Ra)
Colour samples(8 of 14)
Test source
Colour coordinates
ltcolour differencesgt
Standard illuminant
Colour coordinates
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Low CRI and yet high colour preference? CRI and
LEDs subject of international research CIE TC
1-69 Colour Rendition by White Light Sources
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Obstacles efficacyBUT Lighting Systems
Higher Light Output Ratio possible due to a
higher directionality of the naked light source
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Obstacles efficacyBUT coloured applications
LED /Halogen green traffic signal efficiency
(cd/W) 8 / 1
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LED penetration into General Lighting obstacles
lumen maintenance

• LED lifetime is sometimes specified in MTBF (mean
  time between failure).
• Various LED manufacturers predict LED source life
  up to 100K hours
• Lumen Maintenance is even more important.
• End-of-Life specification light output has
  dropped to 70 compared to the original light
  output
• 50.000 hrs !

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LED penetration into General Lighting obstacles
thermal management - chip
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LED penetration into General Lighting obstacles
thermal management - luminaire
Project 2.2 Californian Energy Commission
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LED penetration into General Lighting obstacles
reproducibility
binning
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LED penetration into General Lighting obstacles
price
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Pro and contra pro

• Saturated colours, dynamic colour effects with a
  large colour gamut
• High efficiency for applications with coloured
  light (e.g. traffic lights)
• Liftetime up to 50 000 hours (70 definition)
• Vibration-proof
• Low voltage
• No mercury
• No UV and IR radiation
• Instantaneous switch-on
• Easy dimmable

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Pro and contra contra

• Reproducibility is difficult (semiconductor
  processing) binning (sorting by intensity,
  colour, forward voltage) is required
• Colour and intensity shift with temperature,
  driving current and life time
• Low output/device
• Low efficacy for white (but is improving)
• Price

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• www.lichttechnologie.be

KaHo St.-Lieven Gebr. Desmetstraat 1 B-9000
GENT Tel [phone] Peter.Hanselaer_at_kahosl.
be
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Laboratory for LightLighting

• Founded in 1997 with the support of IWT
  Vlaanderen (Flemish institute for the promotion
  of innovation in science and technology).
• Main activities
• Education
• Scientific research
• Supporting industrial developments

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Topics
Lighting
Optical design
Measurement Facilities
Appearance
Photovoltaics
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Lighting

• Research
• Criteria efficient lighting
• LEDs (PhD)
• Supporting industry
• Groen Licht Vlaanderen promotion of
• energy efficient lighting (Greenlight)
• Shoplighting

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Optical design

• Research
• Luminaire design with ray-tracing (PhD)
• Supporting industry
• Secundary optics for LED clusters
• Surface with uniform luminance

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Appearance

• Research
• Gloss (PhD)
• Colour rendering with LEDs
• Supporting industry
• Automotive
• Wood
• Retro-reflection

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Photovoltaics

• Research
• Spectral response
• Light trapping in cells and modules
• Supporting industry
• Stand-alone systems
• Signalization

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Measurement facilities

• 8/d spectral reflectance and transmittance
• Goniometer
• Spectrometers VIS, UV, near IR
• Electrical characterization
• Bidirectional Scattering distribution
• Photometric/colorimetric camera
• LED integrating sphere