METAL IODIDE LAMP

Description

[0001] This invention relates to metal iodide lamps, and more particularly to metal iodide high intensity discharge (HID) lamps having improved color rendering.

[0002] Metal halide lamps have an inner quartz arc tube containing a fill and are surrounded by an outer glass envelope. The metal halide lamp's arc tube fill includes a rare gas for starting, a quantity of mercury to establish the arc at the desired power level, and one or more metal halides, usually iodides. These metal halides are responsible for a much higher luminous efficacy and color rendering index for the lamp output than is possible for the mercury vapor lamp.

[0003] Certain terms as used in this specification have meanings which are generally accepted in the lighting industry. These terms are described in the IES LIGHTING HANDBOOK, Reference Volume, 1984, Illuminating Engineering Society of North America. The color rendering index of light source (CRI) is a measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature. The CRI rating consists of a General Index, R_a, based on a set of eight test-color samples that have been found adequate to cover the color gamut. The color appearance of a lamp is described by its chromaticity coordinates which can be calculated from the spectral power distribution according to standard methods. See CIE, Method of measuring and specifying colour rendering properties of light sources (2nd ed.), Publ. CIE No. 13.2 (TC-3,2), Bureau Central de la CIE, Paris, 1974. The CIE standard chromaticity diagram includes the color points of black body radiators at various temperatures. The locus of blackbody chomaticities on the x,y-diagram is known as the Planckian locus. Any emitting source represented by a point on this locus may be specified by a color temperature. A point near but not on this Planckian locus has a correlated color temperature (CCT) because lines can be drawn from such points to intersect the Planckian locus at this color temperature such that all points look to the average human eye as having nearly the same color. Luminous efficacy of a source of light is the quotient of the total luminous flux emitted by the total lamp power input as expressed in lumens per watt (LPW or lm/W).

[0004] The luminous efficacy, color rendering index and other lamp output characteristics may be varied, depending upon the particular composition of the metal halides in the arc tube. GTE's Metalarc M100/U lamp, with a NaIScI₃CsI chemistry, has a color rendering index (CRI) of 65, an initial lumens per watt (LPW) of 85, and a 10,000 hour lifetime. In the lighting industry, these specifications are considered very good for standard lighting applications. Each chemical in the lamp fill is chosen to contribute specific effects to the lamp's performance. The alkali metal halides improve the color quality, contribute to lumen output of the lamp through strong emissions, and adjust the current-voltage characteristics. Scandium is added to the lamp as an iodide and as a pure metal. Scandium iodide improves color quality by adding a multitude of lines to the emission spectrum. The elemental scandium chip is used to adjust the metal/iodine ratio in the lamp and to getter oxygen impurities.

[0005] The above chemistry can be modified by the replacement of the element cesium with lithium to form a chemistry of NaIScI₃LiI. The resulting lamp has an improved CRI of 73 while still maintaining the 10,000 hour life and the 85 LPW efficacy. However, a CRI of 73 must be further improved for the excellent color rendering needed for showroom lighting, displays in stores, and decorative illumination, both for indoor and outdoor use.

[0006] Presently available HID lamps, such as the Osram POWERSTAR^R HQI-TS metal halide lamp, have a high CRI on the order of 85 but have a relatively short lifetime of 6000 hours. These lamps have a correlated color temperature (CCT) of 4300 K and LPW of 73 to 80. The POWERSTAR^R lamps depend on a rare earth chemistry, HoI₃, TmI₃, and DyI₃ plus NaI. These lamps generally have a lower LPW than NaI-ScI₃ types and a pronounced decline of LPW with operating time. Lamps of this type are generally designed with a higher wall temperature for the arc tube in order that sufficient concentration of the rare earth elements will be present in the arc discharge. The attendant disadvantage of these lamps is their shortened life, which is a consequence of the elevated operating temperature.

[0007] As set forth in U.S. patent 4,866,342 to Ramaiah, the sodium scandium lamp has achieved popularity due to its very good luminous efficacy and long operating life. The patent describes a metal halide lamp having a discharge sustaining fill within an arc tube consisting essentially of a rare gas, mercury, and the halides of sodium and scandium, characterized in that the fill additionally contains thallium halide in the mole ratio of sodium halide to thallium halide of about 280:1 to 75:1 whereby the luminous efficacy of the lamp is increased without substantially adversely affecting the color rendering index of the lamp. As set forth in column 2, lines 51 to 56, an improvement in the luminous efficacy and the color rendering index occurs within the narrow range of 260:1 to 240:1 mole ratio of sodium halide to thallium halide. As set forth in the example in column 4, the highest reported color rendering index was 62 for Lot B. This patent is illustrative of the sensitivity of HID lamps to various dopants and the unpredictability of lamp performance depending on the various ingredients present in the fill. It is desirable to make further enhancements in luminous efficacy and color rendering index while achieving or maintaining a long lamp life.

[0008] U.S. patent 4,053,805 to Scholz et al relates to a red emitting metal halide arc discharge lamp utilizing a fill of mercury, scandium and lithium iodide. Lithium iodide imparts a red component to the emitted light. Problems encountered with lithium iodide as a lamp fill component, as set forth in the above patent, include lamp starting problems and electrode attack. These problems were reduced by the addition of scandium metal to the fill.

[0009] U.S. patent 4,709,184 to Keeffe et al relates to a metal halide lamp where the fill consists essentially of sodium iodide and scandium iodide in a molar ratio in the range of about 20:1 to 28:1, elemental mercury, scandium, and an inert gas. U.S. patent 4,963,790 of White et al describes a floating frame structure for reducing the sodium electrolysis process.

[0010] U.S. patent 5,057,743 to Keeffe and Krasko relates to a metal halide lamp having a chemical fill including sodium iodide, lithium iodide, and scandium iodide. Although lamps exhibit long life, high luminous efficacy, and good color temperature, a further improvement in the color rendering index would be desirable.

[0011] U.S. patent 3,979,624 (over which claim 1 has been characterised) to Liu et al describes, in column 5, lines 54 to 60, a lamp with a ratio of sodium halide to scandium halide at 11.5:1 with a color rendering index of 56 and a lamp with a ratio of 2.5:1 with a CRI at 69. Column 7, lines 17 to 24, discloses "small amounts" of a rare earth can "be used to supplement the charge-sustaining fill". They teach that rare earth is added in "small amounts", and teach that "small amounts" are 2 mg or less for a 20 mg total fill weight. No improvement in lamp performance or color rendering index is reported for such small additions of rare earth.

[0012] Further halide lamps are disclosed in EP-A-0400980, EP-A-0399288 and Patent Abstracts of Japan, Vol. 3, No. 126 (M-77).

[0013] Because of their superior efficacy and operating life, lamps utilizing a chemical fill of NaIScI₃LiI with a scandium metal getter are highly desirable. However, due to their color rendering properties, their commercial use in certain color-critical applications has been limited.

[0014] According to the present invention, there is provided a discharge lamp including a discharge tube, said discharge tube having a chemical fill for forming an electric discharge during lamp operation, said fill comprising an inert starting gas, mercury, alkali metal iodides consisting substantially of sodium iodide and lithium iodide, scandium iodide, and at least one iodide of a rare earth, characterised in that the molar ratio of said iodide of a rare earth to scandium iodide is between 1:1 to 30:1, and in that the lamp emission has its color temperature between 3000 Kelvin and 5000 Kelvin and its color rendering index greater than 80.

[0015] The iodide of a rare earth and scandium iodide are present in amounts sufficient to form a complex for increasing the density of the rare earth in the discharge gas during lamp operation. Due to the increased density of the rare earth in the discharge gas at lower temperatures of operation, the wall temperature of the arc tube is desirably maintained at a temperature between about 800 to 1000 degrees Celsius so that the resulting lamp has a lifetime in excess of 10,000 hours.

[0016] Certain preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a metal iodide discharge lamp;

FIG. 2 shows the optical spectrum of a prior art NaIScI₃LiI lamp, i.e., a lamp not containing a rare earth in accordance with the present invention;

FIG. 3 shows the optical spectrum of a NaIScI₃LiITmI₃ lamp typical of the present invention; and

FIG. 4 shows efficacy versus time for 3000 hours of operation of a NaIScI₃LiITmI₃ lamp typical of the present invention.

[0017] Referring to FIGURE 1, there is shown the structural features of a metal iodide discharge lamp. The illustrated lamp includes a fused quartz discharge tube or arc tube 1 disposed within an outer sealed glass envelope 11. A pair of electrical conductors 18 and 19, which are sealed into and pass through the stem member 14, are connected to external base member 10 for the flow electrical current from an external source (not shown) for energization of the discharge lamp.

[0018] The arc tube 1 has a pair of spaced apart electrodes 2 and 3 which project into the interior of the arc tube 1 at respective ends. Each electrode 2 and 3 comprises a tungsten rod surrounded by tungsten wire coils. The electrodes 2 and 3 are connected to respective metal foils 4 and 5. The metal foils 4 and 5 are formed of molybdenum and are sealed in the ends of the arc tube 1, typically by pinch sealing. The metal foils 4 and 5 are connected to lead-in conductors 6 and 7 which project outwardly away from opposite ends of the arc tube 1 along the longitudinal axis of the arc tube 1. Arc tube 1 is generally made of fused quartz although other types of material, such as alumina (PCA), yttria, or sapphire, may be used. The arc tube for use in a 100 watt size lamp, for example, has an internal diameter of 10 mm and an arc length of 14 mm.

[0019] The wall temperature of the arc tube 1 is determined by the design parameters. The wall temperature is dependent on multiple factors such as the radiation transmission properties, the thermal conductance, diameter, length, and wall thickness of the arc tube. Providing an evacuated outer jacket tends to increase the arc tube temperature at a fixed power loading. In the present invention, the outer envelope 11 is most preferably evacuated with the outer envelope 11 hermetically sealed to the glass stem member 14. The wall temperature of the arc tube in the lamp of the present invention is preferably between about 800 to about 1000 degrees Celsius.

[0020] The electrodes 2 and 3 are electrically connected to respective electrical conductors 18 and 19. This electrical connection, which is illustrated in detail in Fig. 1, also provides support for the arc tube 1. Lead-in conductor 7 which extends from the lower end of the arc tube 1 is directly connected to conductor 19. Lead-in conductor 6 which extends from the upper end of the arc tube 1 is indirectly connected to conductor 18 through support conductors 25, 27, and 29. Support conductors 27, 29 extend in the same direction away from the longitudinal axis of the arc tube 1 so that interconnecting support conductor 25 extends exterior to the radiation shield 13. As a result, the arc tube 1 is electrically isolated from radiation shield 13. The lead-in conductors 6,7 and support conductors 25, 27 and 29 are sufficiently rigid so as to provide adequate and independent support for arc tube 1.

[0021] The arc tube 1, which is positioned interior to the radiation shield 13, is electrically isolated from the radiation shield 13 and the support structure 12. Such a "floating frame" structure is used to control the loss of alkali metal from the arc tube fill by electrically isolating the support structure. Such a structure is described in U.S. patent 5,056,743 to Krasko et al and in U.S. patent 4,963,790 of White et al which specification is incorporated by reference into the present specification. In particular, the radiation shield 13 is referred to as a heat loss reducing member. The arc tube is disposed within the heat loss reducing member. A support for the heat loss reducing member is electrically isolated from the electrical conductors and the electrodes.

[0022] Within the outer envelope 11, support member 12, which is electrically insulated from the electrical conductors 18 and 19, holds radiation shield 13. Support member 12, which extends substantially parallel to the longitudinal axis of the lamp, is secured to an insulated portion of glass stem member 14 at one end and to outer envelope 11 at the other end. The envelope attachment 15 is in the form of a circular configuration which mates with a dimpled upper partition of the envelope 11 so as to maintain the support structure 12 electrically isolated and properly aligned. A pair of getters 20 and 21 are shown mounted to the support structure 12.

[0023] The radiation shield 13 is secured to the support structure 12 by spaced apart straps 16 and 17 which are welded to a vertically aligned portion of the support member 12. The radiation shield 13 has a cylindrical shape and is typically in the form of a quartz sleeve which can have a domed shaped closure at one end: Each of the straps 16 and 17 is made of a spring-like material so as to hold the shield 13 firmly in position. As set forth in U.S. patent 4,859,899, the diameter and length of the radiation shield may be chosen with respect to the arc tube dimensions to achieve the optimal radiation redistribution resulting in uniform arc tube wall temperatures.

[0024] The lamp may include other structural features commonly found in metal iodide lamps, such as an auxiliary starting device. Although the drawing illustrates a medium screw type base 10. it is contemplated that the lamp may have a double-ended configuration with a recessed single-contact base.

[0025] A chemical fill which forms an electrical discharge sustaining gas for emitting radiation is disposed within the arc tube 1. The chemical fill contains a base chemistry of an inert starting gas, mercury, alkali metal iodides, and scandium iodide. The desired base chemistry contributes to the desirable lamp characteristics of low wall temperature, high LPW, moderate CRI, and long life. The lamp emission due to the base chemistry is approximately on the black body chromaticity locus.

[0026] In addition to the appropriate base chemistry, the chemical fill comprises at least one iodide of a rare earth element which is at least partially vaporized during lamp operation. The iodide of a rare earth and scandium iodide are present in a molar ratio sufficient to form a complex for increasing the concentration of the rare earth in the discharge gases during lamp operation at a low arc tube wall temperature. Due to the formation of the complex, the vapor phase concentration of the rare earth is increased at the arc tube wall temperature beyond what is obtainable using the rare earth iodide alone. The wall temperature of the arc tube in the lamp of the present invention is preferably maintained between about 800 to about 1000 degrees Celsius.

[0027] In accordance with the principles of the present invention, the improved chemical fill comprising the base chemistry and at least one rare earth iodide enhances the color rendering index of the lamp. Due to the presence of the rare earth atoms in the discharge gas, the lamp has a color rendering index greater than about 80. Preferably, the color rendering index is greater than 85 and more preferably greater than 90.

[0028] High color rendering indices, on the order of about 90, are easier to realize at high correlated color temperatures (CCT). In a preferred embodiment, the present invention achieves high R_a at relatively low CCT between 3000 and 4000 Kelvin.

[0029] During lamp operation, the amount of rare earth in the arc is sufficient to produce an enhanced color rendering index while maintaining the relatively low arc tube wall temperature that is conducive to long lamp life. The formation of complex molecules of the rare earth with scandium iodide results in an increased density of rare earth atoms in the arc.

[0030] In the present invention, rare earth is present in an amount sufficient to complex with scandium iodide in order to increase the density of the rare earth atoms in the vapor during lamp operation to the desired level. The molar ratio of the rare earth iodide to scandium iodide in the fill is between 1:1 to 30:1, and more preferably between about 5:1 to about 20:1. A most preferred molar ratio is about 15:1.

[0031] Due to their many emission lines, all rare earths may enhance the arc performance of a lamp, at least to some degree and in some respect. The rare earths are selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof. The choice of rare earth depends on the desired radiation characteristics. The preferred rare earths for enhanced CRI are the iodides of cerium, praseodymium, neodymium, dysprosium, holmium, erbium, thulium, and lutetium. According to one embodiment the rare earth iodide is present as a single rare earth iodide selected from the above preferred group. Even more preferred are the rare earth iodides of cerium, praseodymium, dysprosium, holmium, and thulium.

[0032] A charge of mercury is present in a sufficient amount so as to establish the electrical characteristics of the lamp by desirably increasing the electric field strength to sustain a desirable power loading. Such an amount should provide an operating mercury pressure between 1 to about 100 atmospheres (1 to 100 × 10⁵ Pa), and preferably between about 1 to about 20 atmospheres (1 to 20 × 10⁵ Pa).

[0033] In addition to mercury, a small charge of an inert ionizable starting gas such as argon is contained within the arc tube 1. It is contemplated that other noble gases can be substituted for argon provided an appropriate pressure is maintained that is conducive to starting the lamp.

[0034] To achieve the above discussed desirable lamp properties, the scandium iodide and the alkali metal iodides are present in the fill and in the discharge gas during lamp operation. These ingredients form a base chemistry which is conducive to the low arc tube wall temperature and long lamp life. These ingredients also improve color quality by adding a variety of lines to the emission spectrum and are preferably present in amounts for producing emission with its color substantially on the black body radiator chromaticity locus. The molar ratio of sodium iodide to scandium iodide is between about 5:1 to about 25:1. The ratio of sodium iodide to lithium iodide is between about 1:1 to about 5:1.

[0035] The alkali metal iodides adjust the current-voltage characteristics, stabilize the arc by reducing arc constriction, improve the color quality, and contribute to lumen output of the lamp through strong emissions. In the present invention, the "efficacy" in lumens per watt (LPW) is preferably greater than about 75, and more preferably greater than about 80.

[0036] The addition of a rare earth iodide, according to the preferred embodiments, substantially maintains the LPW near or above 80 while improving the CRI from about 73 to above 80, and while preserving the CCT between 3000 and 5000 Kelvin.

[0037] In the present invention, the selection of fill ingredients results in a desirable color temperature between 3000 K and 5000 K, more preferably between 3000 to about 4000 Kelvin. The molar ratios of the ingredients are selected also so that the resulting emission color is near the highly desirable black body (BB) chromaticity locus at this desired color temperature.

[0038] In addition to the above-mentioned fill ingredients, scandium, thorium, cadmium, or zinc may be added to the fill as metals or alloys to adjust the metal/iodine ratio in the lamp and to getter oxygen impurities. The preferred additive is scandium. For a low wattage metal iodide discharge lamp with a lamp wattage less than 175 watts, e.g., between 40 to 150 watts, the scandium metal weight dosage is preferably about 100 micrograms per cubic centimeter of arc tube volume at all wattages. The total fill weight varies with lamp operating power between about 4 and about 20mg. For example, the 100 watt lamp fill is preferably between about 4mg and about 8 mg, and more preferably between about 5.5 and about 6.5 mg.

AN EMBODIMENT OF THE INVENTION

[0039] For 40-150 watt lamps, the arc tube has a volume of 0.3-2.2 cm³, respectively. The chemical fill has a base chemistry of about 13 to 8 mg/cm³ mercury, respectively, and about 90 to about 150 torr (12 to 20 × 10³ Pa) starting gas; about 0.1 to about 0.5 mg/cm³ scandium iodide; about 1 to about 3 mg/cm³ sodium iodide; about 0.3 to about 0,5 mg/cm³ lithium iodide; about 0.1 to about 0.2 mg/cm³ scandium metal. For the particular rare earth additive, thulium iodide, about 2.5 to about 4 mg/cm³ thulium iodide is included. Preferably the tube has a wall loading in the range of about 12 to 17 watts/cm², respectively, for the 40-150 W lamps. The total amount of fill is between about 4 mg to about 20 mg. Those skilled in the art will recognize that all chemicals introduced into the lamp fill are desirably of the highest purity attainable. Also, it should be recognized that the iodide compound may be synthesized in situ by introducing the constituents in other forms. For example, instead of introducing a rare earth iodide, the rare earth iodide may be synthesized within the arc tube by using, as the lamp fill components, the rare earth metal plus mercury iodide rather than the rare earth iodide plus mercury metal.

EXAMPLES

[0040] The following examples are provided to enable those skilled in the art to understand more clearly and practice the present invention. These examples should not be construed as a limitation upon the scope of the present invention as claimed but merely as being illustrative and representative thereof.

[0041] Two sets of 100-watt metal iodide lamps were made to compare lamps of the present invention with lamps not including scandium iodide in order to demonstrate that scandium iodide acts as a complexing agent component for the rare earth iodide. This first example utilizes thulium iodide. Each of the lamps included a quartz arc tube having an internal volume of about 1.25 cm³, an arc gap of about 14 mm, an electrode insertion length of about 2.5 mm, and an inside diameter of 10 mm. The fill of the arc tube of the first set is set forth in Table 1. The fill components are set forth in weight and in micromoles. The second set of lamps contained the same fill as the first set except for the scandium component. In the second set, no scandium was included. The lamps were operated vertically with their bases up on a standard M90 Advance 100 W ballast. The aging cycle was 10 hours on and 2 hours off.

TABLE I

FIRST SET OF LAMPS
ACTIVE CHEMICAL FILL						GETTER METAL
Hg	NaI	ScI3	LiI	Ar	ReI	Sc
(mg)	(mg)	(mg)	(mg)	(torr)	(mg)	(mg)
13.50	1.53	0.18	0.54	100 (1.3 x 105 Pa)	3.75	0.13
Hg	Na	Sc	Li	I	ReI	Sc
micromoles
67.3	10.2	0.42	4.03	36.0	6.82	2.89

[0042] Substantial rare earth emission was observed in the first set of lamps. Fig. 3 shows the observed emission spectrum between 380 and 800 nm. Indeed the continuum level is truly non-zero, i.e. Fig. 3 shows unresolved or broadened Tm emissions of significant output power as an underlying continuum. In this graph and in Fig. 2, the zero level is a true zero and the continuum level in Fig. 3 is at least twice that in Fig. 2. A spectroscopic abundance determination based on these and other spectra of thulium indicates that the thulium concentration in lamps with the scandium is two orders of magnitude greater than what is expected based solely on the vapor pressure of the non-complexed thulium iodide at the wall temperature. With the scandium free lamp fill, for the same power dissipation, the Tm emissions were weaker by a factor of about 50.

[0043] Thus, at least in the illustrated embodiments, it has been shown that it is possible to increase the color rendering index for an HID lamp utilizing the NaIScI₃LiI chemistry while maintaining the efficacy and long life characteristics of such lamps; to increase the density of the rare earth atoms in the arc without necessitating a detrimental increase in the cold spot temperature; to improve the color rendering properties of the lamp while maintaining a long lamp life; to increase the density of the rare earth species above the density obtainable with a rare earth iodide alone; to increase the density of the rare earth atoms in the arc by forming a complex molecule containing the rare earth element; and to have a wall temperature of the arc tube that is conducive to a long lamp life.

Claims

1. A discharge lamp including a discharge tube (1), said discharge tube having a chemical fill for forming an electric discharge during lamp operation, said fill comprising an inert starting gas, mercury, alkali metal iodides consisting substantially of sodium iodide and lithium iodide, scandium iodide, and at least one iodide of a rare earth, characterised in that the molar ratio of said iodide of a rare earth to scandium iodide is between 1:1 to 30:1, and in that the lamp emission has its color temperature between 3000 Kelvin and 5000 Kelvin and its color rendering index greater than 80.

2. A discharge lamp as claimed in Claim 1 characterised in that said discharge tube operates at a discharge tube wall temperature of between 800 to 1000 degrees Celsius.

3. A discharge lamp as claimed in claims 1 or 2 characterised in that the molar ratio of said sodium iodide to said scandium iodide is between 5:1 to 25:1.

4. A discharge lamp as claimed in claims 1, 2 or 3 characterised in that the molar ratio of said sodium iodide to said lithium iodide is between 1:1 to 5:1.

5. A discharge lamp as claimed in any of the preceding claims characterised in that said at least one iodide of a rare earth is selected from the group consisting of the iodides of cerium, praseodymium, neodymium, dysprosium, holmium, erbium, thulium, lutetium and mixtures thereof.

6. A discharge lamp as claimed in any of the preceding claims characterised in that said scandium iodide and said alkali metal iodides are present in amounts for producing emission with its color substantially on the black body radiator chromaticity locus.

7. A discharge lamp as claimed in any of the preceding claims characterised in that said chemical fill consists substantially of 13 to 8 mg/cm³ mercury and 12 kPa (90 torr) to 20 kPa (150 torr) starting gas; 0.2 to 0.51 mg/cm³ scandium iodide; 1 to 3 mg/cm³ sodium iodide; 0.3 to 0.5 mg/cm³ lithium iodide; and 2.5 to 4 mg/cm³ thulium iodide.

8. A discharge lamp as claimed in any of the preceding claims characterised in that the discharge tube (1) has a total amount of fill between 4 mg to 20 mg.

9. A discharge lamp as claimed in any of the preceding claims characterised in that said discharge tube (1) has a wall loading in the range of 12 to 17 watts/cm².

10. A discharge lamp as claimed in any of the preceding claims characterised in that it further includes a radiation shield (13) and a support (12) therefore, said discharge tube (1) being disposed within said radiation shield, and said support being electrically isolated from said discharge tube.

11. A discharge lamp as claimed in any of the preceding claims characterised in that said lamp has a wattage of 30 to 150 watts.

Ansprüche

1. Entladungslampe mit einer Entladungsröhre (1), welche eine chemische Füllung für die Bildung einer elektrischen Entladung während des Lampenbetriebs aufweist, wobei diese Füllung ein inertes Startgas, Quecksilber und Alkalimetalljodide umfaßt, die im wesentlichen aus Natriumjodid, Lithiumjodid, Scandiumjodid und zumindest einem Jodid einer seltenen Erde bestehen, dadurch gekennzeichnet, daß das Molverhältnis des Jodids einer seltenen Erde zum Scandiumjodid zwischen 1 : 1 bis 30 : 1 beträgt, und daß die Farbtemperatur der Lampenemission zwischen 3000 Kelvin und 5000 Kelvin und ihr Farbwiedergabeindex größer als 80 sind.

2. Entladungslampe nach Anspruch 1, dadurch gekennzeichnet, daß die Entladungsröhre bei einer Entladungsröhrenwandtemperatur von zwischen 800 bis 1000 Grad Celsius arbeitet.

3. Entladungslampe nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß das Molverhältnis des Natriumjodids zum Scandiumjodid zwischen 5 : 1 bis 25 : 1 beträgt.

4. Entladungslampe nach Anspruch 1, 2 oder 3, dadurch gekennzeichnet, daß das Molverhältnis des Natriumjodids zum Lithiumjodid zwischen 1 : 1 bis 5 : 1 beträgt.

5. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche , dadurch gekennzeichnet, daß zumindest ein Jodid einer seltenen Erde aus der Gruppe ausgewählt ist, die aus den Jodiden des Zeriums, Praseodymiums, Neodymiums, Dysprosiums, Holmiums, Erbiums, Thuliums, Luteziums und Mischungen aus denselben besteht.

6. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß das Scandiumjodid und die Alkalimetalljodide in Mengen zur Erzeugung einer Emission vorhanden sind, deren Farbe sich im wesentlichen im Farbart- und Farbsättigungsbereich des Schwarzkörperstrahlers befindet.

7. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die chemische Füllung im wesentlichen aus 13 bis 8 mg/cm³ Quecksilber und 12 kPa (90 Torr) bis 20 kPa (150 Torr) Startgas, 0,2 bis 0,51 mg/cm³ Scandiumjodid, 1 bis 3 mg/cm³ Natriumjodid, 0,3 bis 0,5 mg/cm³ Lithiumjodid und 2,5 bis 4 mg/cm³ Thuliumjodid besteht.

8. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Entladungsröhre (1) eine Gesamtfüllmenge zwischen 4 mg bis 20 mg aufweist.

9. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Entladungsröhre (1) eine Wandladung im Bereich von 12 bis 17 Watt/cm² aufweist.

10. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß sie außerdem einen Strahlungsschild (13) und eine Halterung (12) dafür aufweist, wobei die Entladungsröhre (1) innerhalb des Strahlungsschilds angeordnet ist und die Halterung von der Entladungsröhre elektrisch isoliert ist.

11. Entladungslampe nach irgendeinem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die Lampe eine Leistung von 30 bis 150 Watt besitzt.

Revendications

1. Lampe à décharge incluant un tube à décharge (1), le dit tube à décharge ayant un remplissage chimique pour former une décharge électrique pendant le fonctionnement de la lampe, le dit remplissage comprenant un gaz d'amorçage inerte, du mercure, des iodures de métaux alcalis incluant substantiellement de l'iodure de sodium et de l'iodure de lithium, de l'iodure de scandium, et au moins un iodure d'une terre rare, caractérisée en ce que le rapport molaire entre le dit iodure d'une terre rare et l'iodure de scandium est compris entre 1 et 30, et en ce que l'émission de la lampe a sa température de couleur comprise entre 3000 Kelvin et 5000 Kelvin et son indice de rendu des couleurs supérieur à 80.

2. Lampe à décharge selon la revendication 1, caractérisée en ce que le dit tube à décharge fonctionne à une température de la paroi du tube à décharge comprise entre 800 et 1000 degrés Celsius.

3. Lampe à décharge selon la revendication 1 ou 2, caractérisée en ce que le rapport molaire entre de dit iodure de sodium et le dit iodure de scandium est compris entre 5 et 25.

4. Lampe à décharge selon la revendication 1, 2 ou 3, caractérisée en ce que le rapport molaire entre le dit iodure de sodium et le dit iodure de lithium est compris entre 1 et 5.

5. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que le dit au moins un iodure d'une terre rare est choisi dans le groupe comprenant les iodures de cérium, de praséodymium, de néodymium, de dysprosium, de holmium, d'erbium, de thulium, de lutétium et des mélanges de ceux-ci,

6. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que le dit iodure de scandium et les dits iodures de métaux alcalis sont présents en quantités pour produire une émission dont la couleur est substantiellement sur le lieu de chromaticité du radiateur du corps noir.

7. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que le dit remplissage chimique comprend substantiellement entre 8 et 13 mg/cm³ de mercure, et entre 12 kPa et 20 kPa (entre 90 et 150 Torr) d'un gaz d'amorçage; entre 0,2 et 0,51 mg/cm³ d'iodure de scandium ; entre 1 et 3 mg/cm³ d'iodure de sodium ; entre 0,3 et 0,5 mg/cm³ d'iodure de lithium ; et entre 2,5 et 4 mg/cm³ d'iodure de thulium.

8. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que le tube à décharge (1) a une quantité totale de remplissage comprise entre 4 mg et 20 mg.

9. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que le dit tube à décharge (1) a une charge de paroi comprise entre 12 et 17 Watts/cm².

10. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce qu'elle inclut, en outre, un bouclier (13) du rayonnement et un support (12) de celui-ci, le dit tube à décharge (1) étant disposé à l'intérieur du dit bouclier du rayonnement, et le dit support étant électriquement isolé du dit tube à décharge.

11. Lampe à décharge selon l'une quelconque des revendications précédentes, caractérisée en ce que la dite lampe a une puissance comprise entre 30 et 150 Watts.

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