Table Of ContentLight and Light Sources
P. Flesch
Light and Light Sources
High-Intensity Discharge Lamps
With 226 Figures, 5 in Color , and 4 Tables
123
PD Dr.-Ing. Peter Flesch
OSRAM GmbH
Nonnendammallee 44-61
13629 Berlin
Germany
E-mail:
Dedicated to my family
Preface
High-intensity discharge lamps (HID lamps, also high-pressure discharge lamps)
are very important light sources for visible, UV, as well as IR radiation. They have
captured a major share of the markets for automotive headlight lamps (D2 lamp),
video projection (UHP lamp), general lighting, street/industrial lighting,
commercial lighting, floodlighting, sun tanning, microscopy, endoscopy,
photochemistry, lithography, etc. This renders HID lamps an interesting and seminal
field of research. High-pressure discharge lamps are normally very small (typically
0.7 mm to some centimeters’ electrode gap), have short time scales (typical ac
frequency: 50–500 Hz or higher), and the electrical power input lies between some
tens and several thousand watts. This book is concerned with the understanding of
these lamps.
Beginning with the human eye and an explanation of light and color, the
working principle of different light sources is explained and the light sources are
compared with each other. Starting point is the incandescent lamp, then low- and
high-pressure (high-intensity) discharge lamps are discussed in detail. Furthermore,
a large part of this book deals with important subjects concerning HID lamps like
electrode and plasma physics as well as the state of the art in HID lamp diagnostics
and modeling.
The aim of this book is to give an introduction to the working principle of HID
lamps and to point out challenges and problems associated with the development
and operation of high-pressure discharge lamps. This book is directed at students
interested in high-pressure discharge lamps as well as persons already involved in
the research and development or the usage of HID lamps.
Karlsruhe, January 2006 Peter Flesch
Acknowledgments
Many thanks to Prof. Dr. Neiger, Prof. Dr. Dr. h.c. Thumm, and Prof. Dr. Zissis, as
well as Prof. Dr. Lemmer, the Lichttechnische Institut, and the Fakultät für
Elektrotechnik und Informationstechnik of the Universität Karlsruhe (TH) for all
the support and the stimulating atmosphere.
Furthermore I would like to thank all my colleagues of the Lichttechnische
Institut and all colleagues from other universities and industry with whom I worked
in different BMBF and EU projects or who I met at conferences and workshops.
Special thanks to the BMBF for supporting the projects FKZ 13N7107/0, FKZ
13N7765, and FKZ 13N8073 as well as to the EU for supporting the cost action 529
“Efficient Lighting for the 21st Century”.
Last but not least, many thanks to all the people supporting the work on this
book by discussions, proofreading, and providing many of the images and figures
shown in this book. This book would not have been possible without this support.
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1 Light and Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 The Human Eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1 Rods and Cones and More . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.2 Color Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.1.3 Mixing Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2 Photometric Characteristics of Light Sources . . . . . . . . . . . . . . . . . . . 11
1.2.1 Luminous Flux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.2.2 Luminous Efficacy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.3 Luminous Intensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.2.4 Illuminance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2.5 Color Rendering Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2.6 Correlated Color Temperature . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.3 Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.3.1 Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.3.2 Incandescent Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.3.3 Gas Discharge Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.3.4 Fluorescent Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
1.3.5 Low-Pressure Sodium Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.3.6 High-Pressure Mercury Lamp . . . . . . . . . . . . . . . . . . . . . . . . . 37
1.3.7 High-Pressure Sodium Lamp . . . . . . . . . . . . . . . . . . . . . . . . . 41
1.3.8 Metal Halide Lamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
1.3.9 Other Discharge Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2 Plasma and Electrode Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.1 Gas Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.1.1 Boltzmann Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
2.1.2 Population Density of Excited Atoms . . . . . . . . . . . . . . . . . . . 52
2.1.3 Maxwell Velocity Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.1.4 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.1.5 Pressure or Ideal Gas Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
2.1.6 Collision Frequency and Mean Free Path . . . . . . . . . . . . . . . . 58
xii Contents
2.1.7 Thermal Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.1.8 Local Thermal Equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.2 Plasma Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.2.1 Evaporation and Partial Pressure . . . . . . . . . . . . . . . . . . . . . . . 62
2.2.2 Saha Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
2.2.3 Plasma Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
2.3 Transport Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
2.3.1 Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
2.3.2 Electrical Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
2.3.3 Thermal Conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
2.3.4 Radiative Energy Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
2.4 Electrode Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
2.4.1 Thermal Conductivity of Tungsten . . . . . . . . . . . . . . . . . . . . . 89
2.4.2 Mass Density and Specific Heat of Tungsten . . . . . . . . . . . . . 91
2.4.3 Black Body Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
2.4.4 Electron Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
3 Experimental Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
3.1 Electrode Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
3.1.1 Electrode Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
3.1.2 Bolometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
3.1.3 1-λ Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
3.1.4 Examples of 1-λ Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
3.1.5 2-λ Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
3.1.6 Pyrometry with Plasma Correction . . . . . . . . . . . . . . . . . . . . . 119
3.1.7 Example of (2+1)-λ Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . 126
3.1.8 More Pyrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
3.1.9 Calorimetric Measurements on Electrodes . . . . . . . . . . . . . . . 138
3.1.10 External Laser Heating of Electrodes . . . . . . . . . . . . . . . . . . . 143
3.1.11 In Situ Laser Diagnostics of Work Function . . . . . . . . . . . . . . 145
3.1.12 Monolayer of Sodium on Cathode . . . . . . . . . . . . . . . . . . . . . . 147
3.1.13 Deformation of Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
3.2 Plasma Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
3.2.1 Emission Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
3.2.2 Electrode Fall Voltage and Electric Field of Column . . . . . . . . 156
3.2.3 Plasma Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
3.2.4 Determination of Lamp Pressure . . . . . . . . . . . . . . . . . . . . . . . 166
4 Numerical Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
4.1 Modeling of Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
4.1.1 Cathode Sheath Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
4.1.2 Examples of Electrode Models . . . . . . . . . . . . . . . . . . . . . . . . 175
4.1.3 Cathode and Anode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
4.2 Plasma Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
4.2.1 Description of the Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
4.2.2 Example of a Plasma Column Model . . . . . . . . . . . . . . . . . . . 189
4.2.3 Example of a Plasma Model Including Convection . . . . . . . . . 193
Contents xiii
4.3 Extended models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
4.4 A Self-Consistent Electrode–Plasma Model . . . . . . . . . . . . . . . . . . . . 200
4.4.1 Model Equations and Boundary Conditions . . . . . . . . . . . . . . 202
4.4.2 Numerical Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
4.4.3 Comparing Different Cathode Models . . . . . . . . . . . . . . . . . . . 226
4.4.4 Different Electrode Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . 238
4.4.5 External Laser Heating of Electrodes . . . . . . . . . . . . . . . . . . . 256
4.4.6 D2 Automotive Headlight Lamp . . . . . . . . . . . . . . . . . . . . . . . 278
4.4.7 Mass, Pressure, and Electrode Gap . . . . . . . . . . . . . . . . . . . . . 298
4.4.8 Spot–Diffuse Transition and Time-Dependent Behavior . . . . . 311
4.4.9 Summary: Self–Consistent Electrode–Plasma Model . . . . . . . 320
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
