Influence of plasma dynamics of a sodium discharge on the radiation spectrum
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MA PHYSICS
Influence of Plasma Dynamics of a Sodium Discharge on the Radiation Spectrum S. V. Gavrish ZAO Zenit, Panfilovskii pr. 10, Zelenograd, Moscow, 124489 Russia email: [email protected] Received October 21, 2010
Abstract—The main directions in improving the color rendering index of a highpressure sodium discharge are analyzed theoretically. The spectral characteristics of the sodium–mercury column in the pulsed and ac modes are compared. The effect of an increase in the xenon pressure and the introduction of rubidium and cesium into the charge on the radiation characteristics of pulsed sodium lamps is studied. DOI: 10.1134/S1063780X1311010X
At present, highpressure sodium lamps (HPSLs) operating at alternating current found wide applica tion only for street lighting [1]. In addition to sodium, such lamps are filled with mercury (60–80 wt %) and xenon at a pressure of 20 Torr in the cold state. Using discharge radiation in Na vapors for indoor lighting is impeded for two reasons. (i) The small value of the color rendering index Ra due to the fact that the main part of the radiation energy is concentrated in the yellow–orange spectrum range, which hinders the visual perception of objects. This is connected with low color temperature of sodium lamps Tcol = 1950–2100 K while, according to requirements of international standards on illumina tion, the light source must have Ra not less than 60–70 and Tcol = 2700–3000 K. (ii) The low environmental friendliness of HPSLs due to the presence of mercury in the filling composi tion for such lamps. This work is devoted to studying ways for improving the chromaticity, namely, by means of varying the spectral composition of the radiation due to using the pulsed mode of power supply of mercuryfree lamps and introducing other alkali metals into the filling composition.
sidered below, the light output (LO) of HPSLs of the NAVT 400 type is 115 lm/W at a nominal power of 400 W. According to conclusions of [2], the power balance of a sodium discharge is distributed to nearelectrode losses (6%), visible radiation (30%), UV and IR radi ation (20%), and radiation free thermal losses in the plasma column (44%). The yellow–orange part of the spectrum (560– 610 nm) concentrates 70% of the visible radiation. It is evident that, to improve color characteristics of lamps, it is necessary to achieve an increase in radiation energy in the blue–green and red parts of the spec trum.
THEORETICAL ANALYSIS The HPSL radiation spectrum in the visible range consists of selfreversed and strongly broadened D lines of sodium (589.0 and 589.6 nm). As an example, Fig. 1 presents the spectral radiation distribution obtained in this work for a commercial OSRAM VIA LOX NAVT 400 lamp. In this case, the color temperature is Tcol ≈ 2100 K as the chromaticity coordinates are X ≈ 0.510 and Y ≈ 0.410 [1]. As a result, the total color rendering index in such lamps is Ra ≈ 23. According to the technique con 1082
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Fig. 1. Radiation sp
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