An Investigation Into LED Multiplexing
and Homogenisation
Presenter : Kevin Rogers
Authors: Kevin Rogers, Nigel Copner, Paul Driscoll,
Ron Yandle, Peter Excell, Kang Li
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Contents
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Introduce multiplexing methodology
Introduce Cymtec’s Neolight LED Multiplexer
Building an optical model of the Neolight LED multiplexer
Analysis of the model
Optimisation of the model
Analysis of optimised model
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Why Multiplex?
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LEDs are a very efficient light source with long lifetimes
Narrow emission spectrum of LEDs only allows discrete colours
General lighting and illumination requires white light
Combining multiple wavelengths can produce white light which allows
LEDs to penetrate several markets
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Producing White Light with LEDs
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Neolight LED Multiplexor
• Integrates collimation, colour
mixing and homogenisation into a
single compact package
• High Luminous flux
• High efficiency
• Preserves etendue
• Dynamic colour variation
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Neolight LED Multiplexor
Long Pass
Dichroic Filters
Tapered
Collimators
Light Pipe
Homogeniser
Short Pass
Dichroic
Filters
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Neolight LED Multiplexor – Building an Optical Model
- Sources
• LEDs used are Luminus PT-120
• Top-down modelling approach
using Zemax source radial
component
• Source dimensions, normalised
far field angular distribution, total
luminous flux, and normalised
spectral data inputted into nonsequential component editor
from datasheet
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Neolight LED Multiplexor – Building an Optical Model
– Mechanical Design
• Imported CAD model
• Glass defined from Zemax glass
catalogue
• Relatively simple shapes so little
discrepancy between imported
CAD and Zemax generated
objects
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Neolight LED Multiplexor – Building an Optical Model
– Optical Coatings
• Several optical coatings utilised
including high-reflection, antireflection, long pass filters, short
pass filters
• Zemax has several methods of
defining coatings including ideal
coatings, actual coating recipe,
and coefficients of reflection and
transmission
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Neolight LED Multiplexor – Running an Optical Model
Total
Luminous flux
(lm)
Illuminance
Average
(lm/cm^2)
Max
illuminance
(lm/cm^2)
Min
illuminance
(lm/cm^2)
Illuminance
uniformity
(%)
X
chromaticity
coordinate
Y
chromaticity
coordinate
2458
1092
1131
1054
+-3.5
0.230
0.185
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Neolight LED Multiplexor – Optimisation
Colour
X coordinate
Y coordinate
Red
0.697
0.303
Green
0.171
0.702
Blue
0.144
0.040
• Using LED XY chromaticity
coordinates an illustration of
achievable colour gamut is
possible
• By varying the drive currents of
the LEDs and therefore the
Luminous flux, nearly all CCTs and
a range of colours available
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Neolight LED Multiplexor – Optimisation
• Using Zemax optimisation algorithms it is possible to target specific XY
chromaticity coordinates and hence specific CCTs
• A commonly used CCT is 6504K of the CIE D65 standard illuminant which
is X = 0.31271 and Y = 0.32902
• These can be set as targets in the merit function editor, the luminous flux
for each LED set as variables and optimisation carried out
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Neolight LED Multiplexor – Optimisation
• LED Luminous flux required from each LED to reach 6504K, produced from
optimisation:
Red (lm)
Green (lm)
Blue (lm)
1029
2502
133
• Gives rise to following ratio:
Red 0.2801: Green 0.683 : Blue 0.036
• Within confines of LED operation:
Red (lm)
Green (lm)
Blue (lm)
1008
2450
130
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Neolight LED Multiplexor – Evaluation
Total Luminous
flux (lm)
Illuminance
Average (lm/cm^2)
Max
Illuminance
(lm/cm^2)
Min
Illuminance
(lm/cm^2)
Illuminance
uniformity
(%)
Average X
chromaticity
coordinate
Average Y
chromaticity
coordinate
2228
990
1029
953
+ -3.5
0.312
0.327
Min X
chromaticity
coordinate
Max X
chromaticity
coordinate
Min Y
chromaticity
coordinate
Max Y
chromaticity
coordinate
Av CCT
(K)
CCT Variation
(K)
0.309
0.315
0.322
0.333
6500
+ -271
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Closing Remarks and References
• Demonstrated using an optical model a method of producing a colour
changeable small area source with an excess of 2000lm
• This unlocks many new applications with etendue restrictive systems, and
pushes the boundaries of systems already utilising LED technologies
• Experimental results to be published at Photonics West 2011
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