experimental and simulated straightening of metal halide arcs using power modulation

368 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 1, JANUARY/FEBRUARY 2011

Experimental and Simulated Straightening ofMetal Halide Arcs Using Power Modulation

Jo Olsen and Thomas D. Dreeben

Abstract—Years of research in the fundamentals of acousticallygenerated flows in high-intensity-discharge arc tubes for enhance-ment have recently produced record-breaking performance inconverting wall-plug power to useful white light. In this paper, sim-ulated results show how power modulation produces straightenedarcs in horizontally running lamps. A fully unsteady compress-ible 2-D flow model is used to reproduce observed instantaneouspressure and temperature oscillations, and the results are timeaveraged and rendered to visualize the bulk gas flows. Sound-wavepropagation and induced flows result from full coupling betweenthe oscillating current, the energy balance, the ideal-gas law,and the conservation of mass and momentum on two separatetimescales. Experimental verifications of the instantaneous andtime-averaged effects are included.

Index Terms—Acoustic, arc stability, electronic ballast, high-pressure discharge lamp, metal halide, resonance.

I. INTRODUCTION

FOR OVER 30 years, acoustics have been given a bad namewith respect to metal halide lighting systems [1], [2] with

only a few exceptional references to acoustic enhancement.For example, an elongated mercury-free metal halide lamp wasshown to produce an ecologically superior lamp and ballastsystem with the use of acoustic arc-centering power frequencies[3]. Recent system-optimization efforts have set a new recordabove 50% for the conversion efficiency of wall-plug electricalpower to visible light conversion [4]. Extensions to finite-element models [5]–[7] reported in this paper will providethe understanding of how power modulation induces bulk gasflows in high-intensity-discharge (HID) arc tubes. Experimentalresults provide verification of the model results on the tworelevant timescales of the instantaneous wave motion and thetime-averaged gas flow. The power frequencies driving thelamps are in the optimum range for switching electronics andopen the door for more efficient ballast designs.

Acoustic straightening is a key enabler of these efficiencygains. The straightening mechanisms occur in the lamp ontwo separate timescales [5], [8]. These are the acoustic andstreaming scales, and for the lamp considered in this paper,

Manuscript received January 5, 2010; revised April 28, 2010 and June18, 2010; accepted June 23, 2010. Date of publication November 9, 2010;date of current version January 19, 2011. Paper 2010-ILDC-003.R2, presentedat the 2009 Industry Applications Society Annual Meeting, Houston, TX,October 4–8, and approved for publication in the IEEE TRANSACTIONS ON

INDUSTRY APPLICATIONS by the Industrial Lighting and Displays Committeeof the IEEE Industry Applications Society. This work was supported byOSRAM SYLVANIA.

The authors are with OSRAM SYLVANIA Central Research, Beverly, MA01915 USA (e-mail: [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TIA.2010.2090935

those scales are approximately 0.01 ms and 0.01 s, respectively.Streaming refers to a class of flows in which oscillatory mo-tion causes a net time-averaged fluid motion, arising from theconvective terms of the governing momentum equations [9]–[15]. In HID lamps, streaming flows are caused by standingsound waves, and they are responsible for the acoustic effectsthat matter for performance: arc straightening, arc flicker, andmixing of different chemical species. Streaming velocities arecalculated by time-averaging the instantaneous velocities overthe driven acoustic oscillation.

To facilitate the comparison of the 2-D model and exper-imental results, test lamps were constructed with elongatedarc tubes filled with mercury, metal halide salt, and xenonbuffer gas. The frequency, amplitude, and width of the secondazimuthal resonance were simulated by applying dc waveformswith ripple and quantifying resulting wave fluctuations at fre-quencies above and below those calculated from simplifiedeigenmode calculations. A spatially resolved application ofthe optical detection of acoustic resonances [8] verifies thesimulation results on the acoustic timescale.

The comparison of the simulated results of the model andthe experimental verification is also shown in the streamingtimescale. The amount of arc centering as a function of in-creased power modulation was simulated by again imposing anoscillating signal on top of a dc waveform. Frequencies thatenable arc straightening are known to be close to the secondazimuthal natural frequency [16]. Simulations here are used toshow a more comprehensive picture of straightening: With sim-ulation, we find that, in the range of straightening frequencies,the second azimuthal mode initiates the straightening processbut the first-radial mode subsequently keeps the arc straight.

II. EXPERIMENTAL METHODS

Sample cylindrical lamps were produced out of Polycrys-talline Alumina in cylindrical geometry. The internal di-mensions of the arc tube are 4 mm (inner diameter) by19 mm (inner length), with the tubes containing 3.5-mg rare-earth metal halide salt, 4-mg Hg, and 300-mbar Ar buffergas. The experimental methods used to facilitate the under-standing of how power modulation induces streaming gas flowin HID arc tubes are spatially resolved optical frequency re-sponse to pink noise and measurement of the arc curvaturewith increasing modulation at straightening sweep frequencies.Optical frequency response to pink noise is a small-signaltechnique that is used to identify the frequencies of the acousticresonance modes without disturbing the arc. The temperaturefluctuations produced from the instantaneous wave motion at

0093-9994/$26.00 © 2011 IEEE

OLSEN AND DREEBEN: STRAIGHTENING OF METAL HALIDE ARCS USING POWER MODULATION 369

tens of kilohertz are correlated to the power modulation formeasurement of the resonant reinforcement. Measurement ofarc curvature, or inversely straightening, evaluates the effect ofthe streaming flows resulting from increasing the modulation inthe region of the second azimuthal mode. By employing bothexperimental techniques, comparisons on the two physicallyrelevant timescales with simulations can be made.

The second azimuthal frequency was determined by theoptical-frequency-response method. This technique is used tocompare results of the simulations on the instantaneous-wave-motion timescale. The lamp is operated horizontally with asquare wave superimposed with a small amount of pink noiseripple. The photodiode intensity signal Ipd(t) is correlated withthe lamp power signal P (t) by computing the ratio of the fullycomplex cross power spectrum to the averaged power spectrumof modulation. Averaging is done in the frequency domain. Bydenoting a Fourier transform with a tilde (∼) and a complexconjugate with an ∗, we have

Frequency Response =Ipd

P× P ∗

P ∗ . (1)

The spatially resolved method, with the photodiode placedabove the midplane in the center of the arc, was used, andtwo positions were chosen to make sure the peak we wereidentifying was the second azimuthal and not a higher orderlongitudinal mode. The location and width of the second az-imuthal peak obtained by this spatially resolved optical methodare compared with simulation results.

The design of the experimental setup is intended to takeimages at varying levels of acoustic power modulation forstraightening. This technique is used to compare results of thesimulations on the timescale of the streaming flows. The lampsare powered with a low-frequency (100-Hz) square-wave drivewith added amounts of acoustic modulation. Amplitude mod-ulation is added near the second azimuthal mode (∼100 kHz)from 0% to a level that straightens the arc but does not produceinstabilities. The sweep parameters were chosen for stableoperation from 90 to 110 kHz at a sweep rate of 210 Hz.

The “Tower of Power” experimental setup (Fig. 1) provides aripply 100-Hz square-wave power to the lamp with a dc powersupply and resistive ballast feeding an H-bridge commutator.The modulation is capacitively coupled to the dc rail. Thelamp power is kept constant via a control loop that gentlybumps the dc supply up or down one-tenth of a volt (< 1%)as the lamp impedance changes. The rms of the square-wavecurrent supplied to the lamp without the additional ripple isequal to the dc supplied to the H-bridge. The acoustic poweris supplied as ripple to the square wave, with the ripple sweptover a specified frequency range. The current and voltagewaveforms are captured with an oscilloscope, transferred tothe computer, and multiplied to obtain the lamp power P (t)with Fourier transform P (f). Ensemble averaging is done inthe frequency domain. The spectral power density ratio (SPR)[17] characterizes the amplitude of modulation supplied to thelamp as

SPR(maximum) =Pmax

P (0)(2)

Fig. 1. Basic Tower of Power experimental setup.

Fig. 2. Blackman apodizing function.

where Pmax is the maximum value of P (f) with f restricted tothe values of the imposed sweep. The time series P (t) is sam-pled over a window long enough to include the 1-ms acoustic-damping time interval. The power waveform is apodized usinga Blackman apodizing function (Fig. 2)

blackman(x) =0.42 − 0.5 cos(2πx) + 0.08 cos(4πx)

0.42. (3)

The fast Fourier transform is then used to calculate the SPRof (2).

The lamp is started and operated for 30 min prior to be-ginning the test. At each new amplitude setting, the lamp isoperated for 10 min to allow it to stabilize from the changesfrom the last setting. No electrode instabilities were observed,either from effects of acoustics or arc attachment.

The custom dual monochromator uses the second gratingto reduce the wavelength smear from the first grating. Forexample, the 577- and 579-nm Hg doublet would produce twooverlapped images if only one grating were used. By bouncingthe overlapped image off the second grating (installed upsidedown from a normal dual monochromator), the overlapped im-ages are placed back on top of each other. Small modificationsto the mirror positions were made to improve the imaging.

The monochromator was tuned to 578 nm and slits wereopened to 3-nm bandwidth to include the 577- and 579-nmdoublet. These optically thin lines reflect the arc positionwith respect to temperature and are often used for plasma


Fig. 3. Model’s domain is half of the cylindrical cross section in the positivecolumn.

temperature diagnostics. The radiation in the 3-nm-bandwidthwindow that is not due to the Hg lines is low enough to notdistort the arc position. If the continuum radiation is too high toneglect, image subtraction can be used similar to spectroscopicbackground subtraction techniques. Background images areobtained by scanning the dual monochromator off peak andmonitoring the spectral radiation with a second spectrometer.

III. SIMULATION METHODS

A fully unsteady compressible 2-D flow simulation model[7] simulates both the instantaneous wave motion and thestreaming flow. The physical domain of the model is half ofa cross section of the experimental lamp in the positive column,with a semicircular region of 2-mm radius, as shown in Fig. 3.This is a 2-D formulation which assumes that all properties arehomogeneous in the direction of the arc.

The governing equations describe a fully compressible un-steady flow, coupled with the Elenbaas–Heller equation andOhm’s law for current continuity. For horizontal gas velocityu, vertical velocity v, temperature T , density ρ, and pressure p,the governing equations are{

ρ∂u

∂t

}+

[ρu

∂u

∂x+ ρv

∂u

∂y

]

= −{

∂p

∂x

}+

∂

∂x

(μ

(2∂u

∂x− 2

3Δ

))

+∂

∂y

(μ

(∂v

∂x+

∂u

∂y

)){

ρ∂v

∂t

}+

[ρu

∂v

∂x+ ρv

∂v

∂y

]

= −{

∂p

∂y

}− ρg +

∂

∂x

(μ

(∂v

∂x+

∂u

∂y

))

+∂

∂y

(μ

(2∂v

∂y− 2

3Δ

))

{ρcv

∂T

∂t

}+ ρcvu

∂T

∂x+ ρcvv

∂T

∂y

= −{pΔ} + ε +∂

∂x

(κ

∂T

∂x

)

+∂

∂y

(κ

∂T

∂y

)+

{σE2

} − qrad

{∂ρ

∂t

}+ u

∂ρ

∂x+ v

∂ρ

∂y= −{ρΔ} ,

{p} = {ρRgasT}. (4)

The dilatation is

Δ = div(�u) (5)

and the viscous dissipation in the energy equation is

ε = μ

[2(

∂u

∂x

)2

+ 2(

∂v

∂y

)2

+(

∂v

∂x+

∂u

∂y

)2

− 23Δ2

].

(6)

The curly bracketed terms of (4) are significant on theacoustic timescale: They represent the excitation and propaga-tion of sound waves, balanced by unsteady changes in mass,momentum, and energy. Streaming velocity is defined as

〈�u〉(t) = 1/τ

t∫t−τ

�u(t′) dt′ (7)

where the timescale τ is the period of one acoustically drivenoscillation. The square-bracketed terms of (4) are the convec-tive link from acoustic motion to streaming: Arc motion andstraightening is the result of small repeated perturbations fromthese terms. A more detailed interpretation of these terms isavailable in [9]–[15]. The transport coefficients are based on apure-mercury chemistry, with the amount of mercury adjustedto 6 mg (1.5 times that of the experimental lamp) so thatthe acoustics-free lamp runs with similar current (400 mA at70 W) as the experimental lamp. The pressure dependence of(8) enables the lamp current to be adjusted by varying themercury dose; this is a close analogy of how such dependenceoccurs in a real lamp. The electrical conductivity is parameter-ized as a function of pressure and temperature [18], [19]

σ = 1200√

3patm

pT 0.75e−55820/T 1/(Ω · m). (8)

Thermal conductivity and viscosity are calculated as a func-tion of temperature using thermochemical software [20]. Tomeet the computational demand of resolving the equationson two disparate timescales, the heat loss due to radiation issimplified considerably from its nonlocal nature. This is doneby expressing it as a local function of temperature and pressure[19], [21]

qrad =2.14 × 1018

T

(p

3patm

)e−86000/T W/m3. (9)


Equation (9) has been empirically shown to represent theradiation loss well in pure-mercury lamps [21]. However, ouruse of pure-mercury properties to represent a metal halide fillcauses distortion in the energy balance and the temperatureprofile. Accordingly, we expect to see a discrepancy betweenthe model and experiments in the natural frequencies becausethey are sensitive to the temperature through the speed of sound.

The system is driven by lamp current, and the nature of soundwaves generated is determined by the signal imposed in thecurrent. For electric field E, the current provides a heat sourceσE2 in the energy equation through Ohm’s law as it applies inthe positive column

E =I∫

σ(T ) dA. (10)

The integral of (10) supplies oscillation to the heat source. Itmust be evaluated and updated in (4) at every time step in thecomputation.

Boundary conditions are imposed at the two boundaries inthe domain, as shown in Fig. 3. At the plane of symmetry,we have standard symmetry conditions on the variables of thesecond-order equations

u = 0∂v

∂x= 0

∂T

∂x= 0. (11)

On the inner surface of the arc tube, we have

u = 0

v = 0

T = TW . (12)

with the inner wall temperature TW = 1334 K. This imposedtemperature neglects the ∼100◦ difference between the top andbottom of the arc tube that a bowed arc normally causes. How-ever, this error is unlikely to distort the acoustic response, as thisdepends upon the plasma temperature as a whole, which rangesup to 6000 K. The density ρ satisfies an integral constraint

ρave =1Ac

∫Ac

ρ dA. (13)

This condition is appropriate for ρ because the mass con-tinuity equation [second from the bottom of (4)] that governsit is first order in the spatial derivatives and has no diffusivecomponent. Equation (13) is imposed with ρave = 22.19 kg/m3

in the positive column. This constraint says that, per unitlength along the arc, the total mass of mercury in the positivecolumn remains constant in time. In conjunction with the2-D flow/infinitely long arc-tube assumption, (13) neglects theexchange of mass with the end portions of the arc tube whenthe temperature profile changes during lamp operation. Thepressure p has no boundary conditions or constraints, since the

Fig. 4. Spatially resolved optical frequency response at 1/4 point and midwayalong the arc.

ideal-gas law of (4) is a purely algebraic equation. The systemof equations is driven by imposing an oscillating current

I = I0 + Irip sin(ωt) (14)

where ω is the angular frequency of the ripple and Irip is theamplitude of the ripple. I0 is the dc component which we usein the model as an approximation to the 100-Hz square wavethat drives the experimental lamp. For each amplitude, I0 isadjusted so that the rms current fed into the model (14) matchesthe experimental value of 400 mA. The angular frequency ωcast as a function of time and specified as a sweep to drive thesimulation was the same as in the experimental lamp. Taken to-gether, (4)–(14) form a comprehensive model that incorporatesthe physics of acoustically driven HID lamp flow. Numericalsolutions to the model are obtained using finite-element analy-sis with COMSOL Multiphysics software. The finite-elementmethod breaks up the geometry in Fig. 3 into 1188 elementsand solves a dimensionless discrete approximation of (4) overeach element.

A. Results for Wave Motion

The experimental measurement and the simulation of wavemotion were conducted with attention to keeping the condi-tions of operation the same for comparison purposes. The arcvessel geometry, the gas composition, the electrical drivingwaveforms, and the timescale of examination are comparable.The frequency, amplitude, and width of the second azimuthalresonance were simulated by applying dc waveforms with rip-ple and quantifying resulting wave fluctuations at frequenciesabove and below those calculated from eigenmode calculations.A spatially resolved application of the optical detection ofacoustic resonances [8] verifies the simulation results on theacoustic timescale.

In Fig. 4, the results of the spatially resolved optical fre-quency response to a small amount of pink noise are shown. Theresonance at 98 kHz is the measured second azimuthal. Noticethe peak reversal of the longitudinal resonance at 86 kHz.

This measured result of 98 kHz compares well with thesimulated result of 104 kHz in Fig. 5.


Fig. 5. Simulated frequency response near the second azimuthal mode.

Fig. 6. Simulated pressure wave at the natural frequency of 104 kHz, shownon a half slice through the arc with temperature color map.

At the natural frequency of 104 kHz, Fig. 6 shows that themodel is reproducing the second azimuthal mode.

The width of the peak in both cases is about 1.5 kHz. Theamplitude of the simulated result is taken from the pressurefluctuations near the bottom of the arc tube, where an antinodeexists in the second azimuthal mode. The measured opticalamplitude originates from a fluctuation of the temperature inthe arc core. Nonetheless, the peak height is approximately afactor of five in both the simulation and experiment.

B. Results for Streaming

The results of the model and experiment are compared bythe amount of arc centering as a function of increased powermodulation. The model’s straightening frequency was foundto be 110–130 kHz, 20% higher than that of the experimentallamp. We attribute this difference primarily to the model’sapproximation of the metal halide lamp chemistry as puremercury. Streaming flows are obtained from the model by

Fig. 7. Measured and simulated effect of increased power modulation (SPR)on arc curvature (relative distance of arc center from arc-tube center to upperwall). Zero SPR corresponds to no acoustic excitation.

running over thousands of oscillations and by time-averagingresults over a single oscillation. The simulation is run until thearc reaches and maintains a new steady-state position—the timefor this typically represents 100 ms in real time. The amount ofcurvature is calculated as the distance of the arc centroid abovethe arc-tube center normalized by the arc-tube inner radius.A similar technique is done experimentally through an imageanalysis of the monochromic images of an optically thin lineof mercury that has been used as a plasma diagnostic for arctemperature. An arc with a value of zero curvature would beone that is exactly centered, and a value of one representsan infinitely thin arc all the way at the top of the arc-tubecavity. Measured and simulated arc curvatures are comparedin Fig. 7.

The simulated SPR values were determined by a linearfit of the current peak-to-peak ripple and the measured SPRvalues. In Fig. 7, the experiment and the simulation demonstratetogether how acoustic excitation causes the arc to straighten.Good agreement is obtained on the straightening effect ofacoustic excitation. The largest discrepancies are in the amountof bowing at low SPR with little or no acoustics and in thefrequencies that are required to cause straightening, which are20% higher with the model. These occur as a natural conse-quence of the model’s simplified pure-mercury chemistry.

Simulation results show the streaming-flow pattern of a lampwith straightened arc compared with the buoyant flow of theacoustics-free case in Fig. 8.

The vertical streaming velocities in the center are comparedfor the two cases in Fig. 9.

Here, the effect of acoustics suppresses the net gas velocity,as shown by the green curve compared with the blue one.

Simulation results expose the modes that are associated withstraightening. While the process begins with excitation of thesecond azimuthal mode of Fig. 6, the mode observed afterstraightening is complete is shown in Fig. 10.

This leads to the conclusion that, although straighteningis initiated from a bowed condition by exciting the secondazimuthal mode, the arc is subsequently held straight by thefirst radial mode in Fig. 10. Although the 140-kHz resonantfrequency of the first radial mode is higher than the driven110–130-kHz sweep, sufficient amplitude is excited to keep thearc straight.


Fig. 8. Simulation results. Temperature map and streaming-flow pattern for(on the right) an acoustically straightened arc compared with (on the left) abowed arc with no acoustics. For each case, the arc is oriented perpendicularto the page. Arc-tube walls are around the perimeter of the diagram. Velocityvectors are not to scale.

Fig. 9. Simulation results. Magnitude of vertical streaming velocity 〈v〉 inthe lamp center, with and without acoustic straightening at SPR = 0.152. Thehorizontal axis corresponds to the vertical black line in the center of Fig. 8.

In addition to stable straightening, the model offers a pic-ture of what happens at frequencies that fall outside of thestable straightening range. Arc curvature is shown as a func-tion of time for two different sweeps, namely, 100–120 and110–130 kHz in Fig. 11.

Over the 110–130-kHz range, the arc straightens and remainsstraight. Over this range, the simulation shows no arc motion foran extended period of time, all the way to 0.3 s. At the lowerfrequency range of 100–120 kHz, Fig. 11 shows arc flicker witha period of 10 ms, of which a representative snapshot is shownin Fig. 12.

Here, the arc is narrowed by a jet of gas from the side of thearc tube. The vertical location of the jet and the arc oscillatewith 0.1-mm amplitude, yielding the arc location shown in the

Fig. 10. Simulation results. The first radial mode is found with stable straight-ened arcs.

Fig. 11. Simulation results. Arc location for a straightened arc compared witha case where the sweep frequencies are 10 kHz lower than the stable range of110–130 kHz.

Fig. 12. Simulation results. A snapshot of temperature with streaming veloc-ity at a sweep of 100–120 kHz.


Fig. 13. Simulation results. Acoustic mode found with the sweep of100–120 kHz.

Fig. 14. Simulation results. Streaming-flow pattern at t = 0.0092 s.

blue line in Fig. 11. The acoustic mode that accompanies thiscondition is shown in Fig. 13.

The 100–120-kHz sweep displays a mode that is close to thesecond azimuthal mode but clearly has some other componentin addition. Comparison of the two sweeps shows the sensitivityof stable operation to the frequency range and how stability ofstraightening is associated with the first radial mode in Fig. 10.

The model also illustrates straightening at its onset: Weexamine the early part of the simulation runs (t = 10 ms) whenthe arc is still located above the center and the excited mode isshifting from the second azimuthal in Fig. 6 to the first radial inFig. 10. Fig. 14 shows the streaming-flow pattern in this initialstage.

This shows how the arc is lowered from its initially bowedposition. The green line in Fig. 11 shows that the arc isapproximately halfway through its trajectory to the centeredposition at the time corresponding to Fig. 14.

IV. CONCLUSION

The capacity to straighten the arc of a horizontally runningHID lamp has been demonstrated here. Experimental resultsshow how driving the lamp at the correct acoustic frequen-cies initially excites the second azimuthal mode and enablesoperation with a stable straightened arc. Model results exposethe inner workings of straightening: sound-wave propagationon the acoustic timescale plus arc motion on the streamingtimescale. From the model, we see that the second azimuthalmode initially lowers the arc from its bowed position, but it isthe first-radial mode that keeps the arc straight. The agreementbetween the experimental results and those of the model on thetwo timescales of interest provides verification that the physicalprocesses are well represented. Key mechanisms that we needto understand, predict, and control are brought about throughthis joint experimental modeling approach. Future efforts willenable further advances in HID technology.

ACKNOWLEDGMENT

The authors would like to thank their colleagues who havecontributed to the general knowledge of acoustics in high-intensity-discharge lamps, particularly W. Moskowitz, N. Chen,K. Stockwald, H. Weiss, H. Kaestle, and A. Lenef.

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Jo Olsen received the B.S.E.E. degree from theUniversity of Michigan, Ann Arbor, in 1984and the M.S.E.E. degree from the University ofMassachusetts, Lowell, in 1990, specializing incontrol systems.

He is a Staff Plasma Physicist and anElectrical Engineer with OSRAM SYLVANIACentral Research, Beverly, MA. With a diverselighting research and development career spanning26 years, he has covered topics in acoustics inhigh-intensity-discharge (HID) lamps, low-pressure-

discharge lamps, phosphors, and cathodes, dielectric barrier discharges,dark starting, Langmuir probe measurements, continuous and pulsedballast electronics, high-pressure lamps and cathodes, igniter electronics,and electrodeless discharge lamps and RF power electronics. Among hispublications are 37 patents in the U.S., Japan, and other parts of the world andthree papers on acoustics in HID lamps, which won IEEE First Prize PaperAwards.

Mr. Olsen is the Chair of the 100-year-old Lighting Committee. He has aMaster Black Belt in Six Sigma and is the lead Design for Six Sigma Instructor.He was the recipient of a fellowship in plasma physics from the MassachusettsInstitute of Technology, Cambridge, in 1997.

Thomas D. Dreeben received the B.A. degree inphilosophy and mathematics and the Ph.D. degreein mechanical engineering from Cornell University,Ithaca, NY, in 1985 and 1997, respectively.

He has worked on automotive fuel systems withFord Motor Company and on turbulence with SandiaNational Laboratories. He is currently working onlighting research with OSRAM SYLVANIA CentralResearch, Beverly, MA, where he focuses on fluidmechanics and heat transfer as they pertain to energyefficiency.

experimental and simulated straightening of metal halide arcs using power modulation

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