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Handbook of Optoelectronics Concepts, Devices, and Techniques Volume One John P This article was downloaded by: 10.3.98.104 On: 24 Sep 2021 Access details: subscription number Publisher: CRC Press Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: 5 Howick Place, London SW1P 1WG, UK Handbook of Optoelectronics Concepts, Devices, and Techniques Volume one John P. Dakin, Robert G. W. Brown Incandescent, discharge, and arc lamp sources Publication details https://www.routledgehandbooks.com/doi/10.1201/9781315157009-3 David O. Wharmby Published online on: 11 Oct 2017 How to cite :- David O. Wharmby. 11 Oct 2017, Incandescent, discharge, and arc lamp sources from: Handbook of Optoelectronics, Concepts, Devices, and Techniques Volume one CRC Press Accessed on: 24 Sep 2021 https://www.routledgehandbooks.com/doi/10.1201/9781315157009-3 PLEASE SCROLL DOWN FOR DOCUMENT Full terms and conditions of use: https://www.routledgehandbooks.com/legal-notices/terms This Document PDF may be used for research, teaching and private study purposes. Any substantial or systematic reproductions, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The publisher shall not be liable for an loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. 3 Incandescent, discharge, and arc lamp sources DAVID O. WHARMBY 3.1 Overview of sources 41 3.6.2 Applications of LP mercury 3.2 Light production 42 discharges 52 3.3 Radiation fundamentals 42 3.7 HP discharges 52 3.3.1 Full radiator radiation and 3.7.1 General features of HP limits on emission 42 discharge lamps 53 3.3.2 Absorption and emittance 43 3.7.2 HP metal halide lamps 54 3.3.3 Étendue 43 3.7.3 Operating principles of metal 3.3.4 Use of light in systems 44 halide lamps 55 3.3.5 Color properties and color 3.7.4 Applications of HP discharge temperature of sources 45 lamps 56 3.3.6 Radiation from atoms and 3.8 Electrical characteristics of molecules in extended sources 47 discharges 57 3.4 Incandescent lamps 47 3.8.1 Breakdown and starting in 3.4.1 Emission 47 discharge lamps 57 3.4.2 Tungsten–halogen lamps 47 3.8.2 Steady state electrical 3.4.3 Varieties of tungsten–halogen characteristics 58 lamps 48 3.8.3 AC operation 60 3.4.4 Lamps with integral reflectors 48 3.9 Other methods of excitation of 3.4.5 Lamps with IR reflectors 49 discharges 61 3.4.6 IR sources 49 3.9.1 Pulsed light sources 61 3.5 Discharge lamps with electrodes 49 3.9.2 Dielectric barrier discharges 61 3.5.1 Stable discharge operation of 3.9.3 Excitation by induction and by discharges with electrodes 49 microwaves 61 3.5.2 Electrode regions 50 3.10 LEDs from the perspective of 3.6 Types of LP discharges 51 conventional lighting 62 3.6.1 Low-pressure mercury rare-gas Appendix 3A 63 discharges 51 References 63 3.1 OVERVIEW OF SOURCES general lighting sources, but many are suited to optoelectronic applications. The major lamp com- There is a very wide range of incandescent and panies, and numerous specialty lamp manufactur- discharge lamps. The majority of these are sold as ers also make lamps for applications other than 41 Downloaded By: 10.3.98.104 At: 19:06 24 Sep 2021; For: 9781315157009, chapter3, 10.1201/9781315157009-3 42 Incandescent, discharge, and arc lamp sources general illumination. Examples of these applica- from narrow atomic lines to a full continuum. The tions are: projection, video, film, photographic, types of spectra are often critical for optical appli- architectural, entertainment and other special cations [5] (see Appendix—Oriel Instruments for a effects, fiber optic illumination including numer- selection of spectra). ous medical and industrial applications, photo- In incandescent lamps, the radiation is from the biological processes, photochemical processing, surface of a hot material. In discharge lamps, con- microlithography, solar simulation, suntanning, duction is the result of ionization of the gas; any disinfection, ozone generation, office automation, light emission is a volume process. The task of the scientific applications, heating etc. lamp designer is to ensure that this ionization is LED sources are covered in detail in Chapter 10. also accompanied by copious radiation of the cor- Section 3.10 of this chapter makes some brief rect quality for the application. comments on the applications in which LEDs are competing with conventional lamps. 3.3 RADIATION FUNDAMENTALS This chapter will concentrate on principles and will be illustrated by a number of examples. 3.3.1 Full radiator radiation and These principles should make it possible to under- limits on emission stand the wealth of information in manufacturer’s websites and catalogues. A selected list of manu- Both in incandescent and discharge lamps, elec- facturers is given in Appendix. tron motion is randomized. In all cases of practi- There are a number of useful books about light cal interest, the drift velocity of the electrons in the sources. The book by Elenbaas [1] is an excellent applied electric field is much less than the mean overview of the science of light sources, whilst for velocity. An electron energy distribution function discharge lamps the book by Waymouth [2] con- is established that can usually be characterized by tains clear and detailed explanations of many dis- an electron temperature Te. The distribution func- charge phenomena. Coaton and Marsden [3] give tion may be far from Maxwellian when particle a comprehensive introduction recent enough to densities are low, or under transient conditions. It cover many modern developments; their Appendix is the electrons in the high-energy tail of the dis- gives a useful generic table of lamp data for nearly tribution that excite the atoms, with subsequent every commercial source used for illumination. emission of radiation. Zukauskas et al. [4] give an up to date review of the The spectral radiance Le (λ, T) of the full radia- use of LEDs in lighting. tor or black body is given by Planck’s equation (Chapter 8, where radiometric and photometric 3.2 LIGHT PRODUCTION quantities are also defined). The spectral radiance is plotted in Figure 3.1 for temperatures typical of Most optical radiation is the result of accelerating those found in incandescent and discharge lamps. electrons and causing them to make inelastic col- Convenient units for spectral radiance are Wm−2 −1 −l lisions with atoms, ions, molecules or the lattice sr nm , obtained by multiplying the value of c1 in structure of solids. In the UV, visible and near IR, Chapter 8 by 10−9. the photons are the result of electronic transitions For incandescent or high-pressure (HP) dis- between energy levels of these materials. charge sources the electron temperature Te is close There are exceptions; in synchrotron radiation in value to the temperature T of the solid or vapor, and related processes emission is from accelerated but for low-pressure (LP) discharges in which col- electrons. lisions between electrons and heavy particles are As particle densities increase in the source, the comparatively rare, Te may be very much higher spectral features broaden out until, in incandes- than the gas temperature. The Planck equation cent sources the spectrum is continuous. Discharge therefore forms a fundamental limit to the radiance sources generally emit spectral lines of atoms and that may be obtained from any source in which the molecules that are broadened to an extent depend- electron motion is randomized. This sets a funda- ing on the pressure. Lamps of various types there- mental limit on the spectral distribution, the energy fore emit a wide range of spectral features ranging efficiency and the radiance of the source. Downloaded By: 10.3.98.104 At: 19:06 24 Sep 2021; For: 9781315157009, chapter3, 10.1201/9781315157009-3 3.3 Radiation fundamentals 43 100,000 7,000 K 6,000 K 10,000 5,000 K e 4,000 K 1,000 tral radianc 3,000 K ec Sp 100 2,000 K 10 300 400 500 600 700 800 900 1000 Wavelength (nm) Figure 3.1 Spectral radiance of a full radiator (Wm−2 sr−1 nm−1). The broken line is Wien’s displacement law showing the shift in peak radiance to shorter wavelengths as the temperature increases. 3.3.2 Absorption and emittance 3.3.3 Étendue For radiation falling on a surface For all optical systems geometry determines how much of the radiation generated by the source αλ(),,Ttθ+()λθ,,Tr+λ(),,T θ=1 (3.1) can be used by the optical system. This behavior depends on a very general concept called étendue ε, also known as geometric extent [6–8]. where the fractions ( , T, ), t( , T, ) and r( , α λ θ λ θ λ A definition of étendue is T, θ) are known as absorbance, transmittance and reflectance, respectively. In general, they depend on 2 the wavelength, temperature and angle θ between a ε= ∫∫ cosdθΩA d(msr) (3.3) ray and the normal to the surface. where cos dA is the projected area of the source The spectral emittanceε (λ, T, θ) is the ratio of θ the thermal emission from the surface to that of a under consideration, and dΩ is the solid angle into full radiator (black body) at the same temperature, which it is radiating. Notice that the units are geo- wavelength and angle.
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