US 3842307 A
A high pressure mercury vapor discharge lamp having a quartz glass discharge tube and refractory metal electrodes in an envelope containing metal halides and an inert gas as the additive fill. The discharge tube contains halides of at least three elements which have essentially similar median excitation energy which comprises dysprosium and at least two other rare earth metals. The dysprosium and the at least two other rare earth metals are present in a total amount of from 0.3 to 1.2 mg/cm of arc length which during operation of the lamp provides a saturated vapor pressure and a wall loading of between 8 and 20 W/cm2.
Description (OCR text may contain errors)
United States Patent 11 1 Dobrusskin et al.
1111' 3,842,307 [451 Oct. 15,1974
Larson 3131184 X HIGH PRESSURE MERCURY VAPOR 3,513,344 5 1970 DISCHARGE LAMP w METAL HALIDE 3,514,659 5/1970 Gunglc ct a1. 313/229 X 3,536,947 10/1970 Higashi et a1. 313/229 ADDITIVES 3,662,203 5/1972 Kuhl et al. 313/184 X.  Inventors: Alexander Dobrusskln; Helmut Leyendecker, both of Trufkirchen, German Primary Examiner-Palmer C. Demeo y A t A F Fl & F h f  Assignee: Patent-Treuhand-Gesellschaft fur t omey' or lrm ynn au EFQFFFEEPEEE ml), Munich. Gerrriany 22 Filed: Oct. 9, 1973  ABSTRACT PP N03 404,609 A high pressure mercury vapor discharge lamp having Related Application Data a quartz glass discharge tube and refractory metal electrodes in an envelope containing metal halides and  5831;32 :2 of 1972 an inert gas as the additive fill. The discharge tube contains halides of at least three elements which have  Foreign Application Priority Data essentially similar median excitation energy which comprises dysprosium and at least two other rare Feb. 11,1971 Germany 2106447 earth metals The dysprosium and the at least two other rare earth metals are present in a total amount [if] cCll 313/184, 313/22Pibl31g/l2/3 offrom Q3 to L2 mg/cm ofarc length which during i 225 operation of the lamp provides a saturated vapor pres- 1 o earc l sure and a wall loading of between 8 and 20 W/cm  References Cited UNITED STATES PATENTS 13 Claims, 2 Drawing Figures 3,334,261 8/1967 Butler et a1. 313/229 2 l0 n n 0 6 I1 I ll Ill PAIENIED v 3.842.307 sum 1 or 2 FIG. I
PAINTED 0m 1 51924 SHEEI 2 BF 2 HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMP WITH METAL HALIDE ADDITIVES The present application is a continuation application of Ser.'No. 224,708 filed Feb. 9, 1972, and abandoned with the filing of the present application.
The invention relates to a high pressure mercury vapor (HPMV) electric discharge lamp with metal halide additives. Such lamps comprise a discharge tube of fused silica with electrodes of refractory metal protruding into the discharge tube, spaced apart by a distance which is a multiple of the discharge tube diameter. A foil seal, each, is hermetically bonded to the electrodes. An outer envelope or jacket surrounds the discharge tube.
It is well-known to add several elements in the form of halogen compounds to the mercury. At least one of the additives may be a rare earth metal halide. The color appearance of illuminated objects is affected by the spectral radiation distribution of the illuminant. ln order to obtain a lamp of good color rendering properties dysprosium iodide and thallium iodide were added, for instance, to the mercury fill (see US. Pat. No. 3,452,238). By this means a color rendering index R of about 85 is attained. Briefly, the color rendering index is a measure of the color rendering property and shows the conformity of the color impression of objects illuminated by a light source, with the color impression of the same object when illuminated by a reference illuminant. For further definitions of this and other terms used herein, reference is made to the [ES Lighting Handbook, published by the Illuminating Engineering Society, New York, NY.
It is an object of the present invention to provide a lamp having a still better color rendering index.
SUBJECT MATTER OF THE PRESENT INVENTION The discharge tube, besides containing mercury and a noble or inert gas, contains halides of at least three elements of similar average or median excitation energy, among them at least three rare earth metals in a total amount of from 0.3 to 1.2 mg/cm of arc length. The wall loading of the discharge tube is between 8 and W/cm The selection of elements of possibly identical median excitation energy is of importance to the invention. lf the elements are differently chosen, the radiation of the elements having higher excitation energy would be decreased in view of the presence of elements with lower excitation energy and, consequently, the total radiation would be less, in effect like that in the prior art.
Surprisingly, it was found that the color rendering index obtained is higher than could be expected from a mere superposition of spectra of the individual components. This phenomenon might possibly be explained by the fact that due to the addition of the partial pres- A sures, and the thereby resulting higher total pressure,
the conditions for excitation of each individual component are improved whereby the continuous portion of the spectrum is increased. This favorably affects both luminous efficacy and color rendering. Thus, a color rendering index of more than 95 is obtained, which has never before been achieved with the previously known lamps. This renders the lamp especially suited for il- Preferably, from the group of rare earth metals, dysprosium, holmium and thulium should simultaneously be present in the lamp; other rare earth metals such as erbium, europium or lutetium might be added thereto. Thallium halide, preferably thallium iodide, and cesium halide, preferably cesium iodide are preferred further additives, the latter for stabilization of the discharge. An embodiment of the lamp according to the invention is illustrated in the accompanying figures, wherein:
FIG. 1 shows the lamp in vertical section; and
FIG. 2 the spectral distribution of radiant flux of the lamp.
A typical lamp has a cylindrical discharge tube 1 of fused silica with an inner diameter of 31 mm; the volume is cc. One electrode 2, 3, each, of Th0 activated tungsten, is provided at each end of the envelope. The electrodes 2 and 3 are connected to the leadin wires 6 and 7, respectvely, by means of foil seals 4 and 5. The electrode spacing is mm. Thev ends of the discharge tube are provided with a coating 8 or 9 of zirconium oxide reflecting heat rays. ln vertical or inclined operating position of the lamp, the area of the discharge tube end covered by coating 8 and adjacent screw base 12, is smaller than the area of the other end of the discharge tube covered by coating 9. The discharge tube 1 is mounted with supports 10, 11 in an outer envelope or jacket 13 provided at one end with the screw base 12.
EXAMPLE 1 The discharge tube is filled with: Ar of 30 Torr; 80 mg Hg; 12 mg Tll; 3 mg Csl (the Csl being useful to stabilize the are); 25 mg Hgl 3 mg Tm; 3 mg Ho; and 3 mg Dy. The latter three rare earth elements react with the Hgl (probably disassociated) in the discharge vessel upon being heated, so that the discharge vessel will contain the desired amounts of mercury and the iodides of thulium, holmium and dysprosium. The'design data and the fill quantities apply to a lamp with a wattage input of 3.5 kW, operated with 18 amps. and from a voltage of 380 V. The luminous flux is 325000 lumens, the luminous efficacy 93 lm/W. The correlated color temperature is 6000 K, the color rendering index R is 95.
EXAMPLE 2 Wattage input of the lamp 250 W; the discharge tube has an inner diameter of 14 mm and a volume of 5.3 cc; and an electrode spacing of 25 mm. The fill in the lamp is Ar of 30 Torr, 10 mg Hg, 1 mg Csl, 12 mg Hgl and 1 mg Tm, 1 mg Ho, 1 mg Dy. Upon heating, the Tm, I-lo ad Dy react with the mercury iodide in the discharge vessel so that the discharge vessel will have the desired amounts of mercury and the iodides of thulium, holmium and dysprosium.
EXAMPLE 3 Lamp dimensions and power as in Example 2; fill within the discharge vessel: Ar of 30 Torr; 8 mg Hg; 1 mg Csl; 16 mg Hgl and 1 mg Dy; 1 mg Tm; 1 mg Eu; 1 mg Ho; the Dy, Tin, Eu, and Ho react with the Hgl as the discharge vessel is heated.
FIG. 2 shows the spectral radiant flux distribution standardized to a luminous flux of 1000 lumens of a 3.5 kW lamp in comparison with daylight D 55 having a color temperature of 5500 K. The figure reveals how well the spectral energy distribution of the inventive lamp approximates the daylight curve with a correlated color temperature of 5500 K.
Besides using the lamp of the present invention, due to its good color rendering properties, for high quality color television live pickup and for the lighting of stadiums and exhibition halls, the lamp is also suited, due to its daylight-resembling color, for all places where illumination in addition to daylight is required.
Terbium also appears to be an element useful in the present invention. In the examples, holmium and/or thulium may be replaced by europium or lutetium.
. We claim:
l. A high pressure mercury vapor discharge lamp comprising a quartz glass discharge tube;
electrodes of refractory metal protruding into the discharge tube and spaced by a'distance which is a multiple of the discharge tube diameter;
an envelope surrounding the discharge tube; metal halides and an inert gas as additive fill to the mercury, contained in the discharge tube;
the improvement wherein the discharge tube contains halides of at least three elements which have essentially similar median excitation energy, and which comprise dysprosium and at least two other rare earth metals, said dysprosium and at least two other rare earth metals being present in a total amount of from 0.3 to 1.2
mg/cm of arc length which during operation of the lamp provide a saturated vapor pressure and a wall loading of between 8 and 20 W/cm 2. Discharge lamp as set forth in claim 1, wherein the total amount of rare earth metals is between 0.5 and 0.9 mg/cm of arc length. 7
3. Discharge lamp as set forth in claim 1, wherein heat-accumulating coatings are provided at the end portions of the discharge tube.
4. Discharge lamp as set forth in claim 3, wherein the heat-accumulating coatings comprise ZrO- 5. Discharge lamp as set forth in claim 1, wherein the halides are iodides.
6. The discharge lamp as set fof'th in claim 1 wherein the discharge tube contains the halides of holmium and thulium in addition to that of dysprosium.
7. The discharge lamp as set forth in claim 6 wherein the discharge tube also contains the halide of erbium.
8. The discharge lamp as set forth in claim 6 wherein the discharge tube also contains the halides of thallium and cesium.
9. Discharge lamp as set forth in claim 8, wherein the halides are iodides.
10. The discharge lamp as set forth in claim 1 wherein the discharge tube contains at least two of the halides of holmium, thulium, erbium, europrum, and lutetium, in addition to the halide of dysprosium.
11. The discharge lamp as set forth in claim 1 wherein the discharge tube contains the halide of at least one other element than the said rare earth metals, said other element and said rare earth metals having similar median excitation energy.
12. The discharge lamp as set forth in claim 1 wherein the discharge tube also contains the halides of thallium and cesium.
13. The discharge lamp as set forth in claim 12 wherein said halides are iodides.