24P021-O
Estimation of Xenon Filling Pressure in Mercury-free Metal Halide Lamp by
Optical Emission Line Broadening
発光スペクトルの広がりを利用した
無水銀メタルハライドランプのXe封入圧推定
Hideki Motomura, Kyosuke Enoki and Masafumi Jinno
本村英樹, 榎 恭介，神野雅文
Department of Electrical and Electronic Engineering, Ehime University
3 Bunkyo-cho, Matsuyama 790-8577 Japan
愛媛大学 大学院理工学研究科 〒790-8577 松山市文京町3
In the environmental point of view, non-toxic and environmentally friendly products are demanded. In thefield of light sources, various mercury-free lamps have been studied. For automotive headlamps,mercury-free metal halide lamps have been developed. However, deviation of the xenon filling pressure
affects lamp performance and a non-destructive method to estimate the xenon filling pressure is required.
The authors measured the emission spectra of mercury-free metal halide lamps for several kinds of fillingpressure. By calculating Van der Waals broadening of measured spectra, it is shown that the xenon fillingpressure can be estimated.

1. Introduction
Nowadays, non-toxic and environmentallyfriendly products are demanded. In the field oflight sources, various mercury-free lamps havebeen studied. For automotive headlamps,
considerable research and development of
mercury-free metal halide lamps (MHLs) has
been performed [1–8] and commercial lamps are
already available in the market. In conventional
MHLs, mercury vapor has several importantroles; one of them is to maintain the plasma
impedance high. In the mercury-free MHLs,
substitute metal vapors, such as zinc, areemployed instead of mercury. Moreover, fillingpressure of the buffer gas (xenon) is increased
compared to conventional MHLs, up to or morethan 10 atm. The working pressures of the metal
vapors are determined by working pressure. On
the other hand, xenon working pressure isdetermined by the filling pressure. Therefore,
deviation of the xenon filling pressure affects
lamp performance. Thus, a non-destructive andsimple method to estimate the xenon fillingpressure in automotive mercury-free MHLs which
is applicable in the manufacturing process isrequired.
Previously, the authors proposed a pressure
estimation method from the plasma impedance(lamp voltage and current) measurement in thelamp ignition phase [9]. Although it has a good
estimation accuracy (~0.1 atm), it requires
accumulation measurement of unstable current
value in the ignition phase. In this paper, theauthors propose a pressure estimation methodfrom the optical emission line broadening in thesteady working phase.
2. Experimental ProcedureD4 type mercury-free MHLs were used in thisstudy. The lamps with four different fillingpressures, 10.0, 12.1, 13.5, 15.4 atm, wereprepared. All the lamps have passed themanufacturer’s inspection about the electricalcharacteristics such as voltage, current, power
consumption and the optical characteristics suchas total flux and color coordinate. This means thedeviation of filling pressure from the above
setting values is small, i.e. less than 0.1 atm. At
the steady state working of the lamps, emission
spectra were measured with a monochromator(Bentham, DTMc300, wavelength resolution wasset at 0.05 nm) and a PMT (Hamamatsu, R955).
3. Results and Discussion
At the steady state working, the lamps showedstrong emission of metal vapors at the near IR(infrared) region. Measured emission spectrum atnear IR region at 10 atm is shown as circles inFig. 1. The spectra in this region had four mainpeaks, which are assigned to Na I (818.325 nm,2P1/22D3/2), Na I (819.479 nm, 2P3/22D3/2), Na I(819.482 nm, 2P1/22D5/2), Zn I (820.380 nm,3P23G3). In the high pressure plasma (severaltens atm), the shape of line spectra becomesasymmetric because of Van der Waals broadening
in the quasi-static approximation, whose profile is1.00.5VdW broadening/nm

Intensity / arb. unitsMeasured
Calculated (for each peak)Calculated (sum of three peaks)

0.7
0.6
0.5
0.4
0.3
0.08 0.10 0.12 0.14 0.16 0.18

0.0815820

8258306

Mean square of xenon atom density/nm

Wavelength / nm
Fig. 1. Measured (circles) and calculated (lines)
emission spectra of the mercury-free metal halide
lamp at near IR region at the xenon filling pressureof 10 atmshown as,ΔqsπΔqs Pqs ( )   2(   ) 3 / 2 exp  4(   )  (  0 ),00 
0(  0 ).
(1)Symmetriccontribution
tothespectral
broadening, i.e. pressure broadening, Stark
broadening, etc., were considered as Lorentz
profile, as shown in Eq. (2).
Δ
1.
(2)
Pi ( )  iπ   0  s 2  Δi 2
Calculated spectra for each peak (two peaks near
819.4 nm were combined) by convoluting
Eqs. (1) and (2) are shown as gray lines, and thesum of three peaks is shown as the black thickline, in Fig. 1. It is found that the calculated
profile fits to the measured spectrum well.
The Van der Waals broadening in quasi-staticapproximation, qs, is proportional to square of
number density of the neutral atom which collides
with the radiating atom. In these lamps, xenon
partial pressure is dominant compared to those of
metal vapors (less than 1 atm). Figure 2 shows
calculated Van der Waals broadening value foreach lamp as a function of mean square of xenon
atom density. The xenon density in the steadystate was calculated with assumption of parabolic
temperature profile with 5500 K at the center [10]and 1000 K at the lamp edge. It is found that thecalculated Van der Waals broadening values arealmost proportional to the mean square of xenon

Fig. 2. Calculated Van der Waals broadening
value for each lamp as a function of mean squareof xenon atom density.

atom density. It is shown that the xenon fillingpressure can be estimated by asymmetric line
broadening of emission spectra.
4. Conclusion
The emission spectra for D4 type mercury-free
MHLs were measured and analyzed with xenon
filling pressure of 10.0, 12.1, 13.5, 15.4 atm. By
calculating Van der Waals broadening ofmeasured spectra, it is shown that the xenon
filling pressure can be estimated.
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