US3740605A - High pressure mercury vapor discharge lamp - Google Patents

Abstract

The addition of suitable proportions of mercury iodide and other selected metals to a mercury vapor lamp containing sodium iodide limits the change in operating voltage with time and provides longer life.

Description

United States Patent 1 Divoix et al.

1 1 June 19, 1973' HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMP Inventors: Jacques Climeut Divoix,

Mesnil-le-Roi; Andre Marc V. Taxil, Rueil-Malmaison, both of France Assignee: Claude, Paris, France Filed: Aug. 24, 1971 Appl. No.: 174,535

Foreign Application Priority Data Aug. 27, 1970 France 7031287 US. Cl. 313/229, 313 225 H0lj 61/20 Field of Search 313/229 Primary ExaminerRoy Lake Assistant Examiner-Darwin R. Hostetter Attorney-C. Cornell Remsen, Jr.', Walter J. Baum and Menotti J. Lombardi et al.

[57] ABSTRACT The addition of suitable proportions of mercury iodide and other selected metals to a mercury vapor lamp containing sodium iodide limits the change in operating voltage with time and provides longer life.

2 Claims, No Drawings 1 HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMP BACKGROUND OF THE INVENTION The metal halogenides introduced into high-pressure mercury-vapor lamps are generally iodides and the metal halogenide which is added in the present invention is cesium iodide, cesium having a low ionization 1. Field of the Invention 5 energy. The present invention relates to improvements in high-pressure mercury-vapor electric discharge lamps and, more particularly, to lamps of this type which contain, in addition to mercury, alkali metal halogenides. DESCRIPEFERRED 2. Description of the Prior Art In these lamps, luminous radiation is generally produced either by very concentrated intense emission The following Table 1 shows three examples A, B and rays, as in the case of metals such as thallium, sodium C of fillings for high-pressure mercury-vapor lamps and indium, or by very numerous rays spread over the having a power of 400 watts obtained with an inner entire spectrum as in the case of rare-earth elements or tube having a diameter of 18 mm and a spacing betransition metals such as scandium, hafnium, thorium. tween electrodes of 50 mm. In each example, the left- The lamp is generally formed of an outer glass envelope side column shows the possible pressure and weight and an inner high pressure discharge tube of vitreous limits in torrs (millimeters of mercury) and in millimaterial Such as q grams, respectively, of the filling materials and the The metals are usually introduced into the lamp in 20 right-side column the values used in an embodiment. the form of halogenides more p r icul rly, in the The left hand column lists the various materials in the form of iodides which are highly volatile halogenides. compositions. H V One of the most used iodides is sodium iodide which, I he exam leA relates to addition of yttrium and cedue to its low vapor pressure at the lamp operation sium iodide with mercury iodide in a high-pressure temperature, is gaseous within the discharge region of mercury-vapor lamp already containing iodides of sothe inner tube and liquid about the tube walls. Due to dium (having a characteristic yellow color), of thallium a diffusion phenomenon through the tube walls, the So- (having a green color) and of indium (having a blue dium iodide is decomposed and the sodium leaves the color). inner area resulting in an enrichment of iodine inside The example B relates to addition of yttrium and cethe tube, which restrains the electric discharge phei m iodide with mercury iodide in a high-pressure nomenon causing an increased voltage across electrode mercury-vapor lamp already containing sodium Iodid terminals after a few hundreds of Operation h r and scandium, which have a very close color spectrum. renders lighting difficult. In the example C, compared with the example B, yt-

One of the solutions adopted to slow the sodium diftri m is replaced by thorium and magnesium. fusion is in locating the inner tube within an area of an Yttrium may also be replaced by hafnium, aluminum outer envelope filled with a neutral gas such as nitroand rare earth metals within limits from 0.1 mg to 5 mg. gen, at adequate pressure. Thus lamps are obtained in Although the addition of only one metal is sufficient which the electrode terminal voltage increases less rapit is clear that addition of several metals of the above y with timementioned list may also be convenient.

TABLE 1 w B C Range of pressure and Exam- Exam- Exam- Materials weights ple Range ple Range ple Argon 10 to 40 torrs 20 10 to 40 tons. 20 10 to 40 torrs- 20 Sodium iodide 10 to mg 25 10 to 50 mg 30 10 to 50 mg 30 Tl1alliumi0didc 0.5 to 5 mg Indium iodide. 0.1 to 2.5 mg Cesium iodide 0.5 to 5 mg 2. 5 Mercury iodide 0 to 10 mg. 10 Mercury 50 to 80 mg 75 Yttrium 0.1 to 5 mg l Scandimn. 1 Thorium Magnesium SUMMARY or THE lNVENTlON TABLE 2 It is therefore. an object of the present invention to D E R E E Materials Range x. ange x. provide an improved hlghpressure mercury vapor Argon mm 40mm 20 low 40 mm 20 electric discharge lamp containing an alkali-metal halo- Sodium iodide 25 100 mg 50 40 w 80 mg gcnidc, by including additional materials to maintain 6O Thqlliuflfl iqdide 2 I05 s 3 thc o eratin v )lt' s b't' t' ll t t 'th t' lndmm md'de mg 03 p g u 5 y cons an wl Cesium iodide 0.5 to 10 mg 5 0.5 to 10 mg 5 In such lamps the alkali-metal halogenides, in particmercury iodide 5 to l0 mg g 5 to 20 mg lg ercury l8 l8 ular, may be sodiumhalogcnide and the added materi- Yttrium OJ to 2 mg l 0 l to 2 mg 1 ails may include additions of mercury halogenlde, and Scandium 0.5 to 5 mg 2 a halogenide of easily ionizable metal and a further metal which may be in decreasing order of preference: yttrium, thorium, magnesium, hafnium, aluminum and rare-earth metals.

Table 2 shows two examples of fillings for highpressure mercury-vapor lamps designed to provide a power of 1,000 watts, the burner diameter being 22 Table 3 shows two examples of fillings for highpressure mercury-vapor lamps designed for providing a power of 2,000 watts, the burner diameter being 30 mm and the spacing between electrodes of 145 mm.

It has been observed that the high-pressure mercuryvapor lamps manufactured according to the present invention have an operating voltage which is increased by less than two volts per thousand operation hours, which constitutes a substantial improvement with respect to prior art lamps of which the operation voltage was increasing by eight to fifteen volts per thousand operation hours.

While the present invention has been described in relation to specific embodiments, it is clear that the composition is not limited to the examples and that other variations and modifications may be made within the scope of the invention as set forth in the appended claims.

What is claimed is:

l. A high-pressure mercury-vapor lamp filling comprising a mixture of materials including mercury, sodium iodide, argon, mercury iodide, cesium iodide, yttrium and a further material selected from the group consisting of thallium iodide, indium iodide, scandium, thorium and magnesium.

2. The lamp of claim 1 including an additional further material selected from the group consisting of thallium iodide, indium iodide, scandium, thorium and magnesium.

Claims (1)

1. 2. The lamp of claim 1 including an additional further material selected from the group consisting of thallium iodide, indium iodide, scandium, thorium and magnesium.