FR2621736A1 - High-efficiency electrodeless high-intensity discharge lamp - Google Patents

Abstract

Discharge lamps. A better efficiency and a better colour reproduction are obtained in an electrodeless metal halide discharge lamp by virtue of a new combination of filling substances for the arc tube 10, comprising a sodium halide, a cerium halide and xenon. A preferred physical configuration for the lamp, in which the arc tube 10 is surrounded by a transparent envelope 12 with interposition of a heat barrier 15, further improves the efficiency at high operating temperatures. Application to lighting.

Description

 The U.S. patent application No. 676367, filed November 29, 1984 and assigned to the applicant of the present invention, describes an electrode type lamp, using sodium iodide and a buffer gas consisting of xenon, as fillers for the tube to bow. It is stated in the prior application that the xenon buffer gas exerts a favorable influence on the spectrum of D lines of sodium, and also prevents blocking of the halide which occurs in lamps of the prior art when uses a mercury-containing buffer gas.

 Another U.S. patent application No. 749025, filed June 26, 1985 and also transferred to the plaintiff, describes an arc lamp of sodium iodide of the type without electrodes, in which the filling material of the arc tube comprises sodium iodide, Mercury and xenon iodide in an amount sufficient to limit the transport of chemical energy from the plasma discharge to the walls of the arc tube. In the arc tube filler, mercury iodide is present in an amount less than the amount of sodium iodide, but sufficient for the formation of a certain amount of free iodide near the walls of the tube arc, during lamp operation. Sodium iodide may also be present in the arc tube filler in sufficient quantity to form a condensate reservoir during lamp operation.

 Since the invention represents further improvements to the electrodeless form of the high pressure discharge metal halide lamp mentioned above, and uses some of the above materials for the arc tube, the reader is invited to refer to more details to the two aforementioned patent applications.

 The invention relates generally to high intensity discharge lamps, in which the arc discharge is generated by a solenoidal electric field, and more particularly relates to the use of an original combination of fillers in the part of such a lamp which consists of an arc tube, with the aim that the lamp emits a white color with improved efficiency and better color rendering indices.

 The lamps described in the invention belong to the category called high intensity discharge lamps, because in their basic operation, it is caused that a gas under a medium pressure to raise emits radiation which the wavelength corresponds to the visible range, under the effect of an excitation which is typically produced by the passage of a current in an ionizable gas such as mercury or sodium vapor. In the original category of such high intensity discharge lamps, the discharge current was passed between a pair of electrodes. Because the electrodes of such high intensity discharge lamps with electrodes were susceptible to be strongly attacked by the filling materials of the arc tube, thus causing premature failure of the lamp, the solenoid electric field lamps of this type, developed more recently, have been proposed with the aim of widening the choice of materials filling the arc tube by eliminating the electrodes. Such more recently developed solenoid electric field lamps are described in U.S. patents. Nos. 4,017,764, 4,180,763 and 4,591,759, all sold to the plaintiff, and these lamps generate in the arc tube an arc consisting of a plasma, during the operation of the lamp, of a lamella fully known in l prior art.

Such electrodeless high intensity discharge lamps are, however, affected by a number of problems which essentially result in operating these lamps with poorer efficiency than lamp structures of other types. The efficiency or cacity effect of the lamp here designates the average light output, usually measured in lumens per watt. Lamps without electrodes present a problem of a different type which is that they have lower color rendering properties than is acceptable for use in general lighting. More specifically, general lighting requires that objects illuminated by a particular light source have substantially the same color as when they are lit by natural sunlight. This requirement is measured by known parameters, such as index values of color rendering (CRI) of the
CIE, and CRI values of 50 or higher are considered essential for the commercial acceptance of lamps in most general lighting applications. Another additional requirement for commercial acceptance in general lighting applications relates to the color temperature of the white produced by such a lamp, which is set at about 30000K for the warm white type lamp, at about 35000K for the lamp of the standard white type and at around 4200 or for the lamp of the cold white type, these characteristics being measured by the chromaticity values x and y of the CIE An additional principle generally accepted is that the fact of increasing the yield for Discharge lamps of this type degrade the color rendering properties of the lamp. Thus, although the prior art electrodeless lamps partially meet the foregoing merit criteria, due to the use of some of the arc tube fillers which are employed in the present invention, there has been no hitherto recognized that a particular combination of all these arc tube fillers is necessary to achieve color improvement without adversely affecting the performance of such lamps.

 A main object of the present invention is therefore to provide lamps with a solenoidal electric field which have an improvement both as regards the yield and the color rendering at color temperatures corresponding to white.

 Another object of the present invention is to provide a particular structure for lamps with a solenoidal electric field which optimizes the performance obtained with current arc tube fillers.

 Another important object of the present invention is to functionally associate the arc tube fillers for a solenoidal electric field lamp with the structural configuration of the lamp in a manner that optimizes the performance of the lamp.

 In accordance with the invention, it has been found that a particular combination of fillers in the arc tube of a metal halide arc lamp without electrodes allows the lamp to emit white light with better efficiency and better color rendering.

More specifically, this improved lamp structure includes a transparent arc tube which contains a filler which is free of mercury and which consists of a combination of sodium halide and cerium halide, together with a substantial gas in xenon, in the appropriate weight proportions, to produce an emission consisting of white light with a yield of 200 lumens per watt (lm / W) or more, this being accompanied by color rendering indices (CRI) of at least 50. The color temperature of white for advanced lamps ranges from about 30,000K to about 50,000K, which makes such lamps suitable for general lighting applications.

Sodium and cerium halides useful for the lamp filling considered can be selected from the group comprising bromides, chlorides and iodides, as well as mixtures thereof such as sodium iodide (NaI) and cerium chloride (CeC13). The proportion by weight of cerium halide is maintained at a value not exceeding the proportion by weight of sodium halide in the lamp filling present, in order to obtain the aforementioned characteristics, and the existence in the tube arc of a reservoir of these fillers is desirable to compensate for any loss of the individual constituents during lamp operation. With respect to the relative weight proportions of the aforementioned sodium and cerium halides, it has been found that too much sodium halide decreases the CRI values, while too much cerium halide decreases the lamp efficiency. The white composite light emitted by the lamp containing the abovementioned filling materials corresponds essentially to a discharge emission in high pressure sodium of conventional type, to which has been added visible radiation produced by the cerium halide, which extends continuously over the wavelength region of 400 to 700 nanometers of visible light.

 The improvement brought by the invention is also attributable to the maintenance of defined proportions of xenon in the filling of the lamp. More specifically, replacing mercury with xenon at high pressures to fulfill the barrier or buffer function against unwanted transfer of thermal energy from the arc discharge to the walls of the arc tube, further improves the radiation emission efficiency in the lamp present. First of all, the use of high-pressure mercury vapor asymmetrically widens the emission of the D-lines of sodium in the spectral region of red, which is undesirable, while xenon broadens more symmetrically the emission of D lines of sodium, to produce a more desirable emission in the spectral region of yellow and green. Second, the relatively high excitation energy of xenon, in comparison with mercury, prohibits the radiation of xenon in the lamp present, while energy loss occurs in unwanted spectral regions when using a radiant discharge in mercury. In addition, arc voltages are lower with xenon than with mercury in the lamps present, which makes it easier to start and operate the lamps present. Another performance advantage obtained in the lamps present by replacing mercury with xenon in the filling of the arc tube, is attributable to the relatively lower thermal conductivity of xenon. Such a lower thermal conductivity more effectively avoids undesirable dissociation halides in the arc discharge, with subsequent recombination of the halides on the walls of the arc tube or in the vicinity thereof. The higher efficiency observed in metal halide lamps without electrodes containing the arc tube fillers described above which consist of sodium and cerium halides, when xenon replaces conventional mercury, is apparently attributable the fact that xenon prevents halide blockage by mercury.

The amount of xenon that is used in the filling of the arc tube present to obtain the lamp performance gains indicated above1 is a sufficient quantity, depending on the internal volume of the arc tube, to limit the transfer of energy. thermal by conduction of the arc discharge towards the walls of the arc tube. As indicated above, the xenon buffer gas actively participates in obtaining performance gains, essentially by eliminating the disadvantages that the usual use of a high pressure mercury buffer gas causes in More specifically, xenon may be present in a sufficient amount, establishing a partial pressure in the range of about 8,000 Pa and above at room temperature, or about 80,000
Pa and above at the operating temperature of the lamp of the invention, in order to obtain these performance gains. Increasing the partial pressure of xenon to about 67,000 Pa at room temperature can further improve the performance of the lamp. For example, we tested a lamp with a "pellet box" configuration, which we will describe later in more detail, in which the arc tube measures 20 millimeters in outside diameter and 17 millimeters in height, and is filled with 5 milligrams of NaI and 2.3 milligrams of CeC13, with xenon under a partial pressure of 67000
Pa at ambient pressure. With this lamp, a yield of 203 lm / W and an IRC value of 54 were obtained, with a color temperature of 36990K. Similarly, a large arc tube having the same configuration and filled with 101 milligrams of NaI, 9.8 milligrams of CeC13, 5 milligrams of T1I, and xenon under a partial pressure of 27,000 Pa at room temperature, exhibited an output of 193 lm / W and a CRI value of 50.1 at a color temperature of 3610 K.

 As noted above, the arc tube filler of the invention may contain additional evaporable metal atoms, other than mercury, to introduce yet other radiant species into the arc discharge. The emission color of the lamp can be changed, without adversely affecting performance, by using small amounts of indium halide and lithium halide, to introduce blue and red monochromatic emission respectively, as well as with addition of thallium halide to enhance the emission of color corresponding to green in the discharge of the lamp. Other atoms of modification of the color temperature of the lamp can be used in the discharge of the arc, among which other alkali metals such as cesium, as well as alkaline earth metals, such as barium, and these atoms may further include metals from the rare earth series, to produce continuous radiation over the entire range of the visible spectral region. To illustrate still more useful materials for the filling of the lamp for this last category of atoms of modification of color temperature of the lamp, one can point out that dysprosium, holmium, ytterbium and thulium halides are considered to be chemically compatible with the lamp structure of the type under consideration. It therefore follows that it is advantageously possible to modify the color temperature of the lamps present, without detrimental effect on the yield or the color rendering, when the filling of the arc tube comprises metal ions which produce a monochromatic or continuous radiation. additional types in the visible spectral region, the two types of additional radiating species being able to be present simultaneously. Since all the radiating species in the filling of arc tube present essentially limit the radiation emitted in the visible spectral region, one can also appreciate that the energy losses in such lamps, which decrease the efficiency of the lamp, like losses in the infrared, are thus minimal.

 A preferred lamp configuration, using the arc tube fillers of the present invention, to optimize lamp performance, consists of a cylindrical arc tube having a height less than its outside diameter, with an envelope transparent outer surface arranged around the arc tube by defining a space between the tube and the envelope, and excitation means for transmitting radio frequency energy to the filling of the arc tube. With this configuration, it is possible to operate these lamps improved in the manner of relatively isothermal devices which do not undergo various heat losses which are found in lamps equipped with electrodes, in particular at the walls and ends, and which are also found in lamps without electrodes of the prior art, of the type comprising a relatively long and narrow arc tube. Since the efficiency of high intensity discharge lamps is limited by such heat losses, it becomes desirable to avoid such degradation of performance in a more efficient manner than previously considered possible in prior art high intensity discharge, which is generally operated at cold point wall temperatures below 7500C. By combining the preferred lamp configuration described above with the arc tube fillers of the invention, it is now possible to obtain a lamp operation closer to isothermal conditions, with cold spots around 9000C, with a gain in efficiency attributable to the increased vapor pressure of the lamp filling. In the preferred lamp configuration, the arc tube can be formed by a glass resistant to high temperatures, such as molten quartz, or by an optically transparent ceramic, such as polycrystalline alumina. The filled arc tube produces an arc consisting of a plasma during the operation of the lamp, under the effect of excitation by a solenoidal electric field employed in the lamp, all of this being carried out in a known manner. excitation is created by a magnetic field, which varies in time, to establish inside the tube an electric field which closes completely on itself, which has the effect of producing the discharge at high intensity causing the emission from light. In the preferred lamp configuration, the excitation source comprises an excitation coil which is placed outside the outer envelope of the lamp and which is connected to a power supply via a network of impedance matching. In the preferred lamp, the space between the arc tube and the outer casing can be occupied by means consisting of a barrier for thermal energy, such as metal or quartz wool deflectors, or even by the Such means constituting a thermal barrier advantageously reduce the heat losses from the lamp, which would also be considerable due to the higher operating temperatures of the lamp and the isothermal operating mode of the lamp which is obtained. now.

The following description refers to the accompanying drawings which respectively represent
Figure 1: a side sectional representation of a lamp configuration without electrodes of the invention, employing the composition of arc tube fillers considered; and
Figure 2: An emission spectral diagram for a characteristic lamp structure using the composition of arc tube fillers of the invention.

 FIG. 1 represents an arc discharge lamp without electrodes which comprises an arc tube 10 intended to contain a filling 11. The arc tube 10 consists of a transparent material, such as molten quartz or a refractory ceramic such as agglomerated polycrystalline alumina. As shown, an optimal shape for the arc tube 10, consists of a flattened spherical shape or a short cylindrical shape (for example the shape of a hockey puck or a pill box), with rounded edges.

As shown, the large diameter of the arc tube 10 is also greater than its dimension in the height direction.

An outer casing 12 is placed around the arc tube 10. The outer casing 12 is transparent and it can also be formed by quartz or a refractory ceramic. The outer casing 12 limits the convection cooling of the arc tube 10. A glass wool mat 15 can also be placed between the arc tube 10 and the outer casing 12, to further limit cooling. A primary coil 13 and a radio frequency (RF) power supply are used to excite an arc discharge, consisting of a plasma, in the filling 11. As indicated previously, this configuration comprising a primary coil 13 and an RF power supply 14 constitutes what a high intensity discharge lamp of the solenoidal electric field type is usually called. The solenoidal electric field configuration essentially consists of a transformer which transfers radio frequency energy to a plasma, this plasma constituting a secondary to a single turn for the transformer. An alternating magnetic field which results from the RF current in the primary coil 13, creates in the arc tube 10 an electric field which closes completely on itself. A current flows under the effect of the electric field and an arc discharge occurs in the arc tube 10. Because a more detailed description of such structures of high intensity discharge lamps, of the solenoidal electric field type , is presented in the patents of the USA Nos. 4,017,764 and 4,180,763 cited above, the reader is invited to refer to these documents.

The operating frequency of the RF power supply 14 is for example 13.56 MHz. A characteristic input power applied to the lamp can be in the range of 100 to 2000 watts.

Lamps were constructed having the structure configuration described above, and found to have the spectral emission curve shown in Figure 2. More specifically, the emission curve shown shows the emission d such a high intensity discharge lamp of the solenoidal electric field type, and this lamp has a color temperature of about 39850K, a yield of 182 lm / W and a CRI value of 54.8. The emission represented is a composite emission which is formed by the line spectrum of a discharge in sodium at high pressure, and which further comprises a visible spectral continuum, with in addition the presence of the emission of cerium in the discharge that occurs in the lamp. The filling of the arc tube of this particular lamp included about 100 milligrams of NaI, about 5.1 milligrams of
T1I, approximately 19.8 milligrams of Cet13 and xenon under partial pressure of approximately 27,000 Pa at room temperature. The following examples are given to show other arc tube fillings which have been successfully tried for the metal halide arc lamp structure of the invention.

EXAMPLE I
An arc tube measuring approximately 20 millimeters in outside diameter and 17 millimeters in height was filled with approximately 6 milligrams of NaI, 2.3 milligrams of CeC13, and a partial pressure of xenon of approximately 67,000
Pa at room temperature. The lamp was operated with an input power of approximately 265 watts to produce 203 lm / W and an CRI value of 54, at a color temperature of approximately 36990K which is close to the white oval cold.

EXAMPLE II
An arc tube of the same size as in Example I is filled with about 6.1 milligrams of NaI, 3 milligrams of Cel3 and a buffer gas consisting of xenon under a partial pressure of about 67000 Pa at room temperature . By then operating the lamp with an input power of approximately 206 watts, an efficiency of 195 lm / W was obtained, an IRC value of 49 and a lamp color temperature of approximately 32900K which is close to the colored oval corresponding to warm white.

EXAMPLE III
In this example, an arc tube having the following dimensions was used: external diameter of 15 millimeters and height of 13 millimeters. The filling of the arc tube consisted of approximately 1 milligram of NaI and 1 milligram of CeC13, with xenon under a partial pressure of approximately 67000 Pa at room temperature. When an input power of 202 watts was applied to the lamp, it exhibited an output of 185 lm / W and a CRI value of 57 at a color temperature of about 48560K, which is close to other recognized color ovals corresponding to white.

EXAMPLE IV
An arc tube having the same physical dimensions as in Example I above was filled with 6.1 milligrams of NaI, 1.4 milligrams of CeCl3, 0.5 milligrams of T1I, and xenon under partial pressure about 67,000 Pa at room temperature. With an input power of 204 watts, the lamp had an output of 204 lm / W and a CRI value of 49 at a color temperature of 3381 K, which is close to the color oval corresponding to white standard.

EXAMPLE V
An arc tube having an outside diameter of 54 millimeters and a height of 25 millimeters was filled with about 100 milligrams of NaI, 5.1 milligrams of
T1I, 19.8 grams of CeC13, and xenon under partial pressure of approximately 27,000 Pa at room temperature. When operating with an input power of 1087 watts, the lamp had an output of 182 lm / W, a CRI value of 54.8 and a color temperature of 39850K, which is again close to the oval corresponding to cool white.

 The above lamp embodiments provide optimum performance for a high intensity discharge lamp of the solenoid electric field type containing the present combination of arc tube fillers, which includes sodium halide, cerium halide and a gas consisting of xenon. As we have shown, we obtain an efficiency higher than 200 lm / W, with CRI values of 50 or more, and we can modify the lamp color temperatures in the spectral region of white by adding more d other evaporable metal atoms which radiate in the discharge which occurs in the lamp. The above examples clearly show that such additional radiating species are incorporated into the filling of the arc tube in the form of halide compounds , so that it can evaporate at operating temperatures of the lamp, without requiring an intermediate conversion.

 We have just described a high intensity discharge lamp without electrodes, of very general utility, which has excellent performance. I1 emerges however from the preceding description that it is possible to make various modifications to the specific embodiments envisaged above, without departing from the scope of the invention. It is possible, for example, to incorporate into the filling of the lamp in question small quantities of radiating agents having a color correction function, other than those indicated specifically, provided that these radiating agents are compatible during the operation of the lamp. It is further possible to use physical configurations other than those indicated above for the lamp, to make even better use of the lamp fill materials.

Claims (19)

 1. A metal halide arc lamp without electrodes and containing no mercury, characterized in that it comprises: (a) a transparent arc tube (10) intended to contain an arc discharge; (b) a filling (11) introduced into the arc tube to produce the arc discharge, this filling comprising a sodium halide and a cerium halide, and these halides being selected from the group which comprises bromides, chlorides and iodides, and mixtures thereof, the sodium halide and the cerium halide being combined in weight proportions which are chosen so that the lamp produces a white emission with better efficiency and better color rendering; (c) the fill (12) further comprising xenon in an amount sufficient to limit the transfer of thermal energy from the arc discharge to the walls of the arc tube (10); and (d) excitation means (13, 14) for transmitting radio frequency energy during filling.  2. Lamp according to claim 1, characterized in that the proportion by weight of cerium halide is not greater than the proportion by weight of sodium halide.  3. Lamp according to claim 1, characterized in that the quantity of sodium halide is selected so that a reservoir of sodium halide condensate is present during the operation of the lamp.  4. Lamp according to claim 1, characterized in that the quantity of cerium halide is selected so that a reservoir of cerium halide condensate is present during the operation of the lamp.  5. Lamp according to claim 1, characterized in that the selected quantities of sodium halide and cerium halide establish a reservoir of mixed condensates during the operation of the lamp.  6. Lamp according to claim 1, characterized in that the amount of xenon is sufficient to establish a partial pressure in the range of about 8000 Pa or more at room temperature.  7. Lamp according to claim 1, characterized in that the quantity of xenon is sufficient to establish a partial pressure in the range of about 80,000 Pa and more at the operating temperature of the lamp.  8. Lamp according to claim 1, characterized in that the sodium halide which is selected is sodium iodide.  9. Lamp according to claim 1, characterized in that the cerium halide which is selected is cerium chloride.  10. Lamp according to claim 1, characterized in that the sodium halide which is selected is sodium iodide and the cerium halide which is selected is cerium chloride.  11. Lamp according to claim 1, characterized in that the filling further comprises metal atoms for modifying the color temperature of the lamp.  12. Lamp according to claim 11, characterized in that a combination of these metal atoms introduces emissions into blue, green and red in the emission spectrum of the lamp.  13 Lamp according to claim 11, characterized in that the selected metal atom is thallium.  14. Lamp according to claim 11, characterized in that the metal atoms are present in the filled s sage in the form of metal halide compounds.  15. Lamp according to claim 11, characterized in that the filling comprises rare earth halides, the rare earths being selected from the group which comprises dysprosium, holmium, ytterbium and thulium, to produce continuous radiation additional in the visible spectrum.  16. Lamp according to claim 11, characterized in that the filling comprises metal atoms producing additional monochromatic radiation in the visible spectrum.  17. Metal halide arc lamp without electrodes and containing no mercury, characterized in that it comprises: (a) a transparent arc tube (10) intended to contain an arc discharge, this arc tube ( 10) having a cylindrical shape with a height less than its outside diameter; (b) a transparent outer casing (12) placed around the arc tube and defining a space between the tube and itself; (c) a filling (11) introduced into the arc tube to produce the arc discharge, this filling comprising a sodium halide and a cerium halide, these halides being selected from the group which comprises bromides, chlorides and iodides, as well as mixtures thereof, the sodium halide and the cerium halide being combined in proportions by weight which are chosen so that the lamp emits white light with better efficiency and better color rendering; (d) the fill (11) further comprising xenon in an amount sufficient to limit the transfer of thermal energy from the arc discharge to the walls of the arc tube, as well as to increase the efficiency of the lamp; and (e) excitation means (13, 14) for transmitting radio frequency energy to the filling (11).  18. Lamp according to claim 17, characterized in that a vacuum has been created between the transparent outer casing (12) and the arc tube (11).  19. Lamp according to claim 17, characterized in that the space between the transparent outer casing (12) and the arc tube (11) is occupied by means (15) which constitute a barrier for thermal energy .