Dr. Christoph G. A. Hoelen Profile

Dr. Christoph G. A. Hoelen

Product Architect at Signify NV

SPIE Involvement:

Conference Program Committee | Author

Publications (21)

Proceedings Article | 4 March 2022 Presentation + Paper

Presentation + Paper

Enhancing indoor optical wireless communication system performance by sectorization

Jean-Paul Linnartz, Paul van Voorthuisen, Christoph Hoelen

Proceedings Volume 12022, 120220D (2022) https://doi.org/10.1117/12.2606368

KEYWORDS: Light emitting diodes, Signal detection, Receivers, Photons, Signal attenuation, Optical design, Wireless communications, Transmitters, Optical communications, Free space optical communications, Indoor communication systems, Communication theory

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Proceedings Article | 4 March 2022 Presentation + Paper

Presentation + Paper

LED assessment based on an improved quality factor for LiFi communication

Jean-Paul M. Linnartz, Christoph Hoelen, Paul van Voorthuisen, Thiago Elias Bitencourt Cunha, Haimin Tao

Proceedings Volume 12022, 120220F (2022) https://doi.org/10.1117/12.2611453

KEYWORDS: Light emitting diodes, Quantum wells, Modulation, Signal to noise ratio, Orthogonal frequency division multiplexing, Signal attenuation, Interference (communication), Telecommunications, Quantum efficiency, External quantum efficiency, Wireless communications, Optical communications

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Proceedings Article | 5 March 2021 Presentation + Paper

Presentation + Paper

Challenges and performance of LED-pumped polycrystalline luminescent concentrators

Christoph Hoelen, Wilco Keur, Ivo Durlinger, Dany Benoy, Dominique Bruls, Jannie Baken, Jan Jansen, Ludo Haenen, Barry Mos, Joan Yu, Eric van Grunsven

Proceedings Volume 11706, 1170616 (2021) https://doi.org/10.1117/12.2578142

KEYWORDS: Solar concentrators, Light sources, Light emitting diodes, Projection systems, Luminous efficiency, Light scattering, Light, Commercial lighting

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High luminance light modules have been developed during the past few years based on luminescent concentrators. By using wavelength conversion, the etendue limitation that prohibits brightness increase of light that has been generated is removed, which is the principle of e.g. solar luminescent concentrators and the High Lumen Density (HLD) light engines developed for projection systems. While high-power LEDs are generally limited to a brightness of ca 200 Mnit (2 x 108 lm/m2sr), LED-pumped HLD modules have demonstrated brightness values of more than 1 Gnit. With these light sources requirements can be met for high flux applications with limited source size that are out of reach of LEDs. Such cases are found in e.g. stage and entertainment lighting or in front projection. So far, the luminescent concentrator light sources were based on single-crystalline (SC) converters. In this paper we report on the development of HLD light engines based on LED-pumped polycrystalline (PC) luminescent concentrators and simplified light source architectures. We demonstrate that with LuAG:Ce and LuYAG:Ce PC luminescent concentrators, emitting in the green-yellow spectral range, identical emission spectra and module performance characteristics can be achieved as with SC luminescent concentrators. This is successfully combined with improvements that were made with respect to HLD luminance and module efficacy. Key challenges for the PC luminescent converters are found in the minimization of light scattering. We conclude that with HLD modules based on PC concentrators, over 15 klm @ <70 lm/W can be delivered with a source brightness well over 1 Gnit. By design, the preferred trade-offs can be made between efficiency, luminance, luminous flux, module size, and cost, by which flux values over 20 klm are feasible as well. Thanks to this simplified concept, further optimization for specific applications is enabled, including the application of more temperature-sensitive converter materials for e.g. longer wavelengths.

Proceedings Article | 25 February 2020 Presentation + Paper

Presentation + Paper

Challenges and improvements in LED-pumped luminescent concentrators

Christoph Hoelen, Dominique Bruls, Wilco Keur, Dany Benoy, Jannie Baken, Ivo Durlinger, Jan Jansen, Ludo Haenen, Barry Mos, Joan Yu, Simon Kadijk, Eric van Grunsven

Proceedings Volume 11302, 113020A (2020) https://doi.org/10.1117/12.2543734

KEYWORDS: Light emitting diodes, Solar concentrators, Light sources, Projection systems, Interfaces, Light sources and illumination, Digital Light Processing, Blue light emitting diodes, Rods, Luminescence, LCD projection, Projection devices, Energy conversion efficiency

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Proceedings Article | 1 March 2019 Presentation + Paper

Presentation + Paper

High brightness light sources based on LD-pumped luminescent converters and LED-pumped luminescent concentrators

C. G. A. Hoelen, D. Benoy, H. Cornelissen, A. Vdovin, D. Bruls

Proceedings Volume 10940, 1094015 (2019) https://doi.org/10.1117/12.2511511

KEYWORDS: Solar concentrators, Light emitting diodes, Light sources, Semiconductor lasers, Projection systems, Light sources and illumination, Collimation, Laser systems engineering, Digital Light Processing, Light, Ceramics, High power diode lasers

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Proceedings Article | 6 September 2017 Paper

Paper

Progress in extremely high brightness LED-based light sources

Christoph Hoelen, Piet Antonis, Dick de Boer, Rolf Koole, Simon Kadijk, Yun Li, Vincent Vanbroekhoven, Patrick Van De Voorde

Proceedings Volume 10378, 103780N (2017) https://doi.org/10.1117/12.2275253

KEYWORDS: Luminescence, Light emitting diodes, Projection systems, Light sources, Rods, Lamps, Solid state lighting, LED lighting, Solar concentrators, Digital Light Processing, LCDs

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Proceedings Article | 6 September 2017 Presentation + Paper

Presentation + Paper

High lumen density sources based on LED-pumped phosphor rods: opportunities for performance improvement

Dick de Boer, Dominique Bruls, Christoph Hoelen, Henri Jagt

Proceedings Volume 10378, 103780M (2017) https://doi.org/10.1117/12.2275729

KEYWORDS: Rods, Light emitting diodes, Solid state lighting, Projection systems, Lamps, Blue light emitting diodes, Waveguides, Light sources

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Proceedings Article | 29 April 2016 Paper

Paper

LED-based projection source based on luminescent concentration

Dick K. G. de Boer, Dominique Bruls, Christoph Hoelen, Henri Jagt

Proceedings Volume 9896, 989606 (2016) https://doi.org/10.1117/12.2225614

KEYWORDS: Light emitting diodes, Light sources, Light, Projection systems, Projection systems, Light emitting diodes, Solar concentrators, Compound parabolic concentrators, Light sources and illumination, Refractive index, Digital Light Processing, Blue light emitting diodes, Mirrors

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Proceedings Article | 8 March 2016 Paper

Paper

Progress in characterizing the multidimensional color quality properties of white LED light sources

Kees Teunissen, Christoph Hoelen

Proceedings Volume 9768, 976814 (2016) https://doi.org/10.1117/12.2217661

KEYWORDS: Light sources, Light emitting diodes, Visualization, LED lighting, Solid state lighting, Human vision and color perception, Radium, Gallium, Lamps, Halogens, Colorimetry

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Proceedings Article | 8 March 2016 Paper

Paper

LED light engine concept with ultra-high scalable luminance

Christoph Hoelen, Dick de Boer, Dominique Bruls, Joost van der Eyden, Rolf Koole, Yun Li, Mo Mirsadeghi, Vincent Vanbroekhoven, John-John Van den Bergh, Patrick Van de Voorde

Proceedings Volume 9768, 976810 (2016) https://doi.org/10.1117/12.2224042

KEYWORDS: Compound parabolic concentrators, Luminescence, Light emitting diodes, Projection systems, Light sources, Light, Digital Light Processing, LED lighting, General lighting, Projection devices, Lamps, Blue light emitting diodes, Solar concentrators, Digital micromirror devices, Solids, Interfaces

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Proceedings Article | 3 February 2009 Paper

Paper

Color-consistent LED modules for general lighting

Christoph Hoelen, Peter van der Burgt, Paul Jungwirth, Matthijs Keuper, Kwong Man, Claudia Mutter, Jan-Willem ter Weeme

Proceedings Volume 7231, 72310A (2009) https://doi.org/10.1117/12.816465

KEYWORDS: Light emitting diodes, LED lighting, Blue light emitting diodes, Light sources and illumination, Control systems, General lighting, Temperature metrology, Lamps, Translucency, Feedback loops

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Proceedings Article | 12 September 2008 Paper

Paper

Remote phosphor LED modules for general illumination: toward 200 lm/W general lighting LED light sources

Christoph Hoelen, Huub Borel, Jan de Graaf, Matthijs Keuper, Martijn Lankhorst, Claudia Mutter, Lars Waumans, René Wegh

Proceedings Volume 7058, 70580M (2008) https://doi.org/10.1117/12.799502

KEYWORDS: Light emitting diodes, Blue light emitting diodes, LED lighting, Luminous efficiency, Diffusers, General lighting, Lamps, Garnet, Temperature metrology, Coating

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Proceedings Article | 26 September 2007 Paper

Paper

Etendue conserved color mixing

R. van Gorkom, M. van As, G. Verbeek, C. G. A. Hoelen, R. Alferink, C. Mutsaers, H. Cooijmans

Proceedings Volume 6670, 66700E (2007) https://doi.org/10.1117/12.733748

KEYWORDS: Light emitting diodes, Optical filters, Collimators, Lamps, Reflectivity, Photography, Collimation, Light, Light sources and illumination, Diffusion

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Proceedings Article | 12 September 2006 Paper

Paper

Color tunable LED spot lighting

C. Hoelen, J. Ansems, P. Deurenberg, W. van Duijneveldt, M. Peeters, G. Steenbruggen, T. Treurniet, A. Valster, J. W. ter Weeme

Proceedings Volume 6337, 63370Q (2006) https://doi.org/10.1117/12.694799

KEYWORDS: Light emitting diodes, Sensors, Temperature metrology, RGB color model, Lamps, Control systems, Light sources and illumination, Light sources, Collimators, LED lighting

Read Abstract +

A new trend in illumination is to use dynamic light to set or dynamically vary the ambience of a room or office. For this we need color tunable spots that can reliably vary over at least a wide range of color temperatures, and preferably also more saturated colors. LEDs are in principle ideally suited for this application thanks to their nature of emitting light in a relatively narrow band. For color tunable spot lighting based on the concept of mixing RGB LED colors, the key results have been presented before. Limitations of these 3-intrinsic-color mixing systems with high color rendering properties are found in a limited operating temperature range due to wavelength shifts, a limited color temperature range, and a low maximum operating temperature due to a strong flux decrease with increasing temperature. To overcome these limitations, a 3-color R_pcGB system with phosphor-converted red (R_pc) and a 4-color RAGB system have been investigated. With both systems, a CRI of at least 80 can be maintained over the relevant color temperature range of approximately 2700 K to 6500 K. In this paper we compare these concepts on overall system aspects and report on the performance of prototype spot lamps. The main features of the RAGB and R_pcGB spot lamp concepts can be summarized as: 1) The RAGB spot overcomes CRI and gamut shortcomings of RGB light sources and gives much freedom in wavelength selection, but suffers from temperature sensitivity and complex controls; 2) The R_pcGB spot overcomes shortcomings concerning CRI and thermal dependence of RGB sources and enables relatively simple controls, but needs an improved overall red efficacy. With both color concepts, prototype spot lamps have been built. The amber to red emitting nitridosilicate-based phosphors can be wavelength-tuned for optimal performance, which is found at a peak emission around 610 nm for high color quality systems. This results in a simple and very robust system with good color consistency. For the RAGB system, a spot lamp has been developed, consisting of a 4-chip light source, an optical system with mixing rod that provides color homogenization and beam shaping, and an electronic drive and control unit based on temperature feed forward. Flux- and color-rendering performance can be tuned according to the application requirements.

Proceedings Article | 2 September 2005 Paper

Paper

Multi-chip color variable LED spot modules

C. Hoelen, J. Ansems, P. Deurenberg, T. Treurniet, E. van Lier, O. Chao, V. Mercier, G. Calon, K. van Os, G. Lijten, J. Sondag-Huethorst

Proceedings Volume 5941, 59410A (2005) https://doi.org/10.1117/12.623010

KEYWORDS: Light emitting diodes, Light sources and illumination, RGB color model, Temperature metrology, Collimators, Scattering, LED lighting, Reflectors, Diffusers, Silicon

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The unique features of light emitting diodes (LEDs) such as intrinsic color generation and relative low temperature operation enable completely new lighting concepts. The ongoing increase in performance of LEDs reaching efficacy levels of more than 30 lm/W for illumination grade white light with the promise of reaching over 75 lm/W makes them also applicable for higher luminous applications such as spot and flood lighting, accent lighting and architectural lighting. For the new lighting feature of ambiance creation, which requires at least variation of the color temperature of the light and preferably also selection of more saturated colors, LEDs are ideally suited. In this paper we report on the overall system aspects to color variable LED spot lighting and on the performance of prototype spot modules. Mixing of the light is performed within the lighting module by a combination of dense packing of red/amber, green and blue emitting dice, and light collimation with facetted optics and small angle diffusion, resulting in a homogeneous appearance of the light source and a color point inhomogeneity Δu'v' in the beam (>90% of total flux) of less than 0.01. A color rendering index (R_a8) of over 80 can be obtained over a large temperature and color temperature range with the 3-color system for a specific combination of 5 nm wide wavelength bins. In the prototype spot modules, between 9 and 14 dice are mounted on a common substrate and integrated with the primary collimating optics that is based on total internal reflection. Nominal power of the spot module is 10W. The average thermal resistance between the die junctions and the housing is 2 K/W. The optical efficiency of the module is 70%. The maximum luminous flux in the beam, which has a full width at half maximum (FWHM) of 20-25°, is about 200 lm. The system has thermal and optical sensors that provide the signals for a closed control loop to compensate for run-up and differential ageing effects. The resulting color point accuracy in the u'v' color space is better than 0.01. This shows the feasibility of easy-to-use lighting modules that offer advanced lighting options with adjustable, reliable and accurate output.

Proceedings Article | 2 September 2005 Paper

Paper

Achieving color point stability in RGB multi-chip LED modules using various color control loops

P. Deurenberg, C. Hoelen, J. van Meurs, J. Ansems

Proceedings Volume 5941, 59410C (2005) https://doi.org/10.1117/12.623020

KEYWORDS: Light emitting diodes, Sensors, Temperature metrology, Calibration, Light sources and illumination, Photodiodes, LED lighting, RGB color model, Control systems, Actuators

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Proceedings Article | 15 July 1999 Paper

Paper

Photoacoustic tissue scanning (PATS)

Christoph Hoelen, Roy Kolkman, M. Letteboer, Ralph Berendsen, Frits de Mul

Proceedings Volume 3597, (1999) https://doi.org/10.1117/12.356826

KEYWORDS: Sensors, Tissue optics, Photoacoustic spectroscopy, Scattering, Blood, Tissues, Light scattering, Breast, Absorption, Signal detection

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Proceedings Article | 30 December 1998 Paper

Paper

Imaging of cutaneous blood vessels using photoacoustic tissue scanning (PATS)

Christoph Hoelen, Frits de Mul

Proceedings Volume 3566, (1998) https://doi.org/10.1117/12.334361

KEYWORDS: Sensors, Tissue optics, Photoacoustic spectroscopy, Blood vessels, Tissues, Scattering, Blood, Light scattering, Absorption, Acoustics

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Proceedings Article | 13 January 1998 Paper

Paper

Photoacoustic blood cell detection and imaging of blood vessels in phantom tissue

Christoph Hoelen, Richard Pongers, G. Hamhuis, Frits de Mul, Jan Greve

Proceedings Volume 3196, (1998) https://doi.org/10.1117/12.297931

KEYWORDS: Photoacoustic spectroscopy, Blood, Blood vessels, Tissue optics

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Proceedings Article | 11 December 1996 Paper

Paper

Photoacoustic location of optical absorbers in phantom tissue

Christoph Hoelen, G. Hamhuis, Niko Pagoulatos, Iris van den Ham, Frits de Mul, Jan Greve

Proceedings Volume 2927, (1996) https://doi.org/10.1117/12.260657

KEYWORDS: Tissue optics, Signal detection, Sensors, Photoacoustic spectroscopy, Blood, Optical fibers, Capillaries, Blood vessels, Scattering, Near field optics

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Pulsed photoacoustic (PA) signals may be used for the detection and imaging of blood vessels in tissue. A relatively strong absorption by red blood cells and low absorption by the surrounding tissue, combined with a reasonable penetration depth of the light is found at a wavelength of ca. 577 nm. Experiments were performed with a pulsed frequency doubled Nd:YAG laser which delivered 10 ns pulses at 532 nm wavelength. Ten percent dilutions of India ink and 50% suspensions of red blood cells in PBS were used as optical absorbers. Blood vessels were simulated by hollow nylon fibers with an inner diameter of ca. 250 micrometer through which these suspensions flow. The optical scattering of the surrounding tissue was simulated by a 12% dilution of Intralipid-10% to get a solution with a reduced scattering coefficient of 1.8 mm^-1. The PA signals were detected with a hydrophone that contained four wide band piezoelectric transducers made of 9 micrometer thick PVdF film with an effective diameter of 200 micrometers. Laser pulses with energies up to 8 microjoules were delivered to the sample by a 50 or 100 micrometer core diameter glass fiber. Pulsed optical heating of red blood cells up to 30 - 35 degrees for more than 12,000 times did not affect the photoacoustic response of the cells. If a single fiber is used to illuminate the sample, then even at a depth of 1 mm the PA signals show that the volume that is effectively illuminated is laterally restricted to a diameter of ca. 1 mm. Vessels with blood or ink dilutions were detected up to a depth of more than 1 mm in the scattering medium. Monte- Carlo (MC) simulations were used to simulate the spatial distribution of light absorption in phantom tissue. From this distribution the PA response of blood vessels was simulated. A delay-and-sum beam forming algorithm was developed for 3-D near field configurations and applied to a PA image reconstruction program. The images based on MC simulations as well as experimental data show that the side of larger vessels that is facing the illuminating fiber can be located with a resolution that depends on the configuration and varies between 0.1 and 1 time the inner vessel diameter. This shows the principle and the feasibility of three dimensional photoacoustic dermal tissue imaging.

Proceedings Article | 15 January 1996 Paper

Paper

Nondestructive photoacoustic subsurface tissue imaging: a feasibility study

Christoph Hoelen, Frits de Mul, Jan Greve

Proceedings Volume 2628, (1996) https://doi.org/10.1117/12.230000

KEYWORDS: Signal detection, Sensors, Spherical lenses, Acoustics, Light scattering, Tissue optics, Signal generators, Scattering, Tissues, Ferroelectric polymers

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Showing 5 of 21 publications

Proceedings Volume Editor (1)

SPIE Conference Volume | 18 August 2009

Ninth International Conference on Solid State Lighting

Conference Committee Involvement (20)

Light-Emitting Devices, Materials, and Applications XXIX

27 January 2025 | San Francisco, California, United States

Light-Emitting Devices, Materials, and Applications XXVIII

29 January 2024 | San Francisco, California, United States

Light-Emitting Devices, Materials, and Applications XXVII

30 January 2023 | San Francisco, California, United States

Light-Emitting Devices, Materials, and Applications XXVI

24 January 2022 | San Francisco, California, United States

Light-Emitting Devices, Materials, and Applications XXV

6 March 2021 | Online Only, California, United States

Light-Emitting Devices, Materials, and Applications XXIV

3 February 2020 | San Francisco, California, United States

Light-Emitting Devices, Materials, and Applications

4 February 2019 | San Francisco, California, United States

Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXII

29 January 2018 | San Francisco, California, United States

Sixteenth International Conference on Solid State Lighting and LED-based Illumination Systems

9 August 2017 | San Diego, California, United States

Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XXI

30 January 2017 | San Francisco, California, United States

Fifteenth International Conference on Solid State Lighting and LED-based Illumination Systems

31 August 2016 | San Diego, California, United States

Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XX

15 February 2016 | San Francisco, California, United States

Fourteenth International Conference on Solid State Lighting and LED-based Illumination Systems

12 August 2015 | San Diego, California, United States

Thirteenth International Conference on Solid State Lighting and LED-based Illumination Systems

20 August 2014 | San Diego, California, United States

LED-based Illumination Systems

26 August 2013 | San Diego, California, United States

Twelfth International Conference on Solid State Lighting and Fourth International Conference on White LEDs and Solid State Lighting

13 August 2012 | San Diego, California, United States

Eleventh International Conference on Solid State Lighting

22 August 2011 | San Diego, California, United States

Tenth International Conference on Solid State Lighting

2 August 2010 | San Diego, California, United States

Ninth International Conference on Solid State Lighting

3 August 2009 | San Diego, California, United States

Eighth International Conference on Solid State Lighting

11 August 2008 | San Diego, California, United States

Showing 5 of 20 Conference Committees

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