An Investigation Into LED Multiplexingand Homogenisation

Presenter : Kevin Rogers

Authors: Kevin Rogers, Nigel Copner, Paul Driscoll, Ron Yandle, Peter Excell, Kang Li

A Guiding Light In Innovation

A Guiding Light In Innovation

Contents

• 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?

• 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

Tapered Collimators

Short Pass Dichroic Filters

Long Pass Dichroic Filters

Light Pipe Homogeniser

Neolight LED Multiplexor – Building an Optical Model - Sources

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• 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 non-sequential component editor from datasheet

Neolight LED Multiplexor – Building an Optical Model – Mechanical Design

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• Imported CAD model• Glass defined from Zemax glass

catalogue• Relatively simple shapes so little

discrepancy between imported CAD and Zemax generated objects

Neolight LED Multiplexor – Building an Optical Model – Optical Coatings

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• Several optical coatings utilised including high-reflection, anti-reflection, 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

Neolight LED Multiplexor – Running an Optical Model

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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

Red (lm) Green (lm) Blue (lm)

1029 2502 133

• LED Luminous flux required from each LED to reach 6504K, produced from optimisation:

• 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