Patent Grant
6979958
This invention relates to high intensity arc discharge lamps and more particularly to high intensity arc discharge metal halide lamps having high efficacy.
Due to the ever-increasing need for energy conserving lighting systems that are used for interior and exterior lighting, lamps with increasing lamp efficacy are being developed for general lighting applications. Thus, for instance, electrodeless fluorescent lamps have been recently introduced in markets for indoor, outdoor, industrial, and commercial applications. An advantage of such electrodeless lamps is the removal of internal electrodes and heating filaments that are a life-limiting factor of conventional fluorescent lamps. However, electrodeless lamp systems are much more expensive because of the need for a radio frequency power system which leads to a larger and more complex lamp fixture design to accommodate the radio frequency coil with the lamp and electromagnetic interference with other electronic instruments along with difficult starting conditions thereby requiring additional circuitry arrangements.
Another kind of high efficacy lamp is the arc discharge metal halide lamp that is being more and more widely used for interior and exterior lighting. Such lamps are well known and include a light-transmissive arc discharge chamber sealed about an enclosed a pair of spaced apart electrodes and typically further contain suitable active materials such as an inert starting gas and one or more ionizable metals or metal halides in specified molar ratios, or both. They can be relatively low power lamps operated in standard alternating current light sockets at the usual 120 Volts rms potential with a ballast circuit, either magnetic or electronic, to provide a starting voltage and current limiting during subsequent operation.
Such lamps may have a ceramic material arc discharge chamber that usually contains quantities of NaI, TlI and rare earth halides such as DyI3, HoI3, and TmI3 along with mercury to provide an adequate voltage drop or loading between the electrodes. Lamps containing those materials have good performance on Correlated Color Temperature (CCT), Color Rendering Index (CRI), and a relatively high efficacy, up to 95 lumens-per-watt (LPW). Of course, to further save electric energy in lighting by using more efficient lamps, high intensity arc discharge metal halide lamps with even higher lamp efficacies are needed. More electric energy can be saved by dimming such lamps in use when full light output is not needed through reducing the electrical current therethrough, and so high intensity arc discharge metal halide lamps with good performance under such dimming conditions are desirable for many lighting applications. However, under these dimming conditions when lamp power is reduced to about 50% of rated value, such ceramic material chamber arc discharge metal halide lamps radiate light in which the color rendering index decreases significantly through having a strong green hue due to relatively strong Tl radiation. Thus, there is a desire for arc discharge metal halide lamps having higher efficacies and better color performance under dimming conditions.
The present invention provides an arc discharge metal halide lamp for use in selected lighting fixtures having a discharge chamber with light permeable walls of a selected shape bounding a discharge region of a selected volume through which walls a pair of electrodes are supported in the discharge region separated from one another by a separation length. The walls also have an effective inner diameter over the separation length in directions substantially perpendicular to the separation length with the separation length being in a ratio to the effective inner diameter that is greater than four. Ionizable materials are provided in the discharge region of the discharge chamber comprising a quantity of mercury in a ratio to the discharge region volume that is less than 4 mg/cm3, a noble gas, a praseodymium halide, and a sodium halide.
The discharge chamber can have walls formed of polycrystalline alumina, and can be enclosed in a transparent bulbous envelope positioned in a base with electrical interconnections extending from the discharge chamber to the base. The ionizable materials can further include a cerium halide, and the praseodymium halide and the sodium halide can be PrI3 and NaI, respectively. The ratio of the mercury quantity to the discharge region volume can be less than 1 mg/cm3.
Referring to
Access wire 15, however, with the first bend therein past flare 16 directing it away from the envelope length axis, is bent again to have the next portion thereof extend substantially parallel that axis, and further bent again at a right angle to have the succeeding portion thereof extend substantially perpendicular to, and more or less cross that axis near the other end of envelope 11 opposite that end thereof fitted into base 12. The portion of wire 15 parallel to the envelope length axis passes through an aluminum oxide ceramic tube, 18, to prevent the production of photoelectrons from the surface thereof during operation of the lamp, and also supports a conventional getter, 19, to capture gaseous impurities. A further two right angle bends in wire 15 places a short remaining end portion of that wire below and parallel to the portion thereof originally described as crossing the envelope length axis which short end portion is finally anchored at this far end of envelope 11 from base 12 in a borosilicate glass dimple, 24.
A ceramic arc discharge chamber, 20, configured about a contained region as a shell structure having polycrystalline alumina walls that are translucent to visible light, is shown in one possible configuration in FIG. 1. Chamber 20 has a pair of small inner and outer diameter ceramic truncated cylindrical shell portions, or tubes, 21a and 21b, that are shrink fitted into a corresponding one of the two open ends of the primary chamber structure, 25. Primary chamber structure 25 has a larger diameter truncated cylindrical shell portion between the chamber ends and a very short extent smaller diameter truncated cylindrical shell portion at each end with a partial conical shell portion there joining the smaller diameter truncated cylindrical shell portion there to the larger diameter truncated cylindrical shell portion.
Chamber electrode interconnection wires, 26a and 26b, of niobium each extend out of a corresponding one of tubes 21a and 21b to reach and be attached by welding to, respectively, access wire 14 at its end portion crossing the envelope length axis and to access wire 15 at its portion originally described as crossing the envelope length axis. This arrangement results in chamber 20 being positioned and supported between these portions of access wires 14 and 15 so that its long dimension axis approximately coincides with the envelope length axis, and further allows electrical power to be provided therethrough to chamber 20.
In addition, a tungsten electrode coil, 32a, is integrated and mounted to the tip portion of the other end of the first main electrode shaft 31a by welding, so that electrode 33a is configured by main electrode shaft 31a and electrode coil 32a. Electrode 33a is formed of tungsten for good thermionic emission of electrons while withstanding relatively well the chemical attack of the metal halide plasma. Lead-through wire 29a serves to dispose electrode 33a at a predetermined position in the region contained in the main volume of arc discharge chamber 20. A typical diameter of interconnection wire 26a is 0.9 mm, and a typical diameter of electrode shaft 31a is 0.5 mm.
Similarly, in
A further lamp structural consideration is the ratio of the arc chamber electrode separation length or distance, “L”, to the arc chamber wall effective inner diameter, “D”, (or, alternatively, the effective inner radius) over that electrode separation distance. This ratio is a significant factor in choosing the arc chamber configuration along with the chamber total contained volume (which forms the discharge region) insofar as the ratios of quantities of active materials contained therein to that volume. This aspect ratio of L to D influences the amount of light being radially emitted from the arc chamber, the excited state distribution of active material atoms, the broadening of the material emission lines, etc. In addition, smaller arc chamber effective diameters will reduce the self-absorption of strong radiating spectral lines of the radiating metals in arc chambers. The increase of self-absorption with increasing arc chamber effective diameters will reduce lamp efficacy (see FIGS. 3 and 4). If a long lamp life is to be achieved, the arc chamber power wall loading must be limited to some maximum value, about 30 to 35 W/cm2 for low wattage metal halide lamps with ceramic arc discharge chambers. At higher power loadings, typically, the chemical reactions of the active material salts with the arc chamber walls and the frit material become so severe that there is substantial difficulty in obtaining sufficient useful operating lives from such devices.
The arc chamber electrode separation length and the arc chamber effective diameter or radius over that separation length cannot be independently chosen. For smaller arc chamber effective diameters, the arc chamber electrode separation length has to be increased to reduce or eliminate the otherwise resulting increase arc chamber wall loading by increasing the inner wall area. In maintaining a fixed wall loading value, the longer the arc chamber electrode separation length, the smaller the arc chamber effective diameter or radius can be. In the situation of holding the ratio of arc chamber electrode separation length to arc chamber effective diameter or radius fixed, the greater the wall loading value that can be accepted, the greater the resulting efficiency in generating light radiation by the metal halide discharge arc in the arc chamber until that efficiency reaches a limiting value. Lamps should have arc chambers with ratios of L/D that are greater than four for reasonable operating efficiencies, and lamps having relatively larger ratios of L/D, at about 7 to 9, have been found to give the highest lamp efficiencies (see FIGS. 3 and 4).
A parameter for characterizing arc discharge lamps, termed normalized wall loading (watts/arc tube diameter), combines the effects of wall loading and radiation trapping phenomena into one combined measure thereof. As can be seen from
Arc chamber 20 can be configured with alternative geometrical shapes different from the configuration of
Thus, every alternative configuration has its advantages and disadvantages. That is, for specific active materials and other lamp characteristics, certain arc chamber configurations have more advantages than do others.
In a first implementation of the present lamp, arc discharge chamber 20 is made from polycrystalline alumina to have a cavity length in the contained discharge region of about 36 mm, for the configuration thereof shown in
In a second implementation of the present lamp, another metal halide is added therein and a shorter but wider arc chamber of the same configuration otherwise is used. The cavity length of arc discharge chamber 20 in this instance in the contained discharge region is about 28 mm with the inner diameter of the chamber between the electrodes being about 5 mm, and the electrodes were spaced apart to provide an arc length of about 24 mm. The rated power of the lamp is again 150 W. The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 2.2 mg Hg and 15 mg of the metal halides PrI3, CeI3 and NaI in alternative PrI3:CeI3:NaI molar ratios of 0.5:1:15.75,0.88:1:19.69, or 2:1:31.5. Again, Xc gas was provided in this region at a pressure of about 330 mbar at room temperature as an ignition gas.
A further set of implementations are given as examples in the following differing from the implementations given above to indicate various ranges contemplated in the present invention. A table of tabulated corresponding photometry results for each of these examples is presented thereafter for operation at full rated power and at half rated power with both conditions at line voltage and with current being limited accordingly.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 0.5 mg Hg and 15 mg total of metal halides NaI and PrI3 in a molar ratio of PrI3:NaI=1:3.5. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.45 cm3 and the arc length between the electrodes is 32 mm. Wall loading is 31 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 0.5 mg Hg and 10 mg total of metal halides NaI and PrI3 in a molar ratio of PrI3:NaI=1:3.5. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.45 cm3 the arc length between the electrodes is 32 mm. Wall loading is 31 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 0.5 mg Hg and 10 mg total of metal halides NaI and PrI3 in a molar ratio of PrI3:NaI=1:7. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.45 cm3 and the arc length between the electrodes is 32 mm. Wall loading is 31 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 0.5 mg Hg and 12.5 mg total of metal halides NaI and PrI3 in a molar ratio of PrI3:NaI=1:7. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.45 cm3 and the arc length between the electrodes is 32 mm. Wall loading is 31 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 0.5 mg Hg and 10 mg total of metal halides NaI and PrI3 in a molar ratio of PrI3:NaI=1:10. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.45 cm3 and the arc length between the electrodes is 32 mm. Wall loading is 31 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 2.2 mg Hg and 15 mg total of metal halides PrI3, CeI3 and NaI in molar ratios of PrI3:CeI3:NaI=0.5:1:10.5. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.55 cm3 and the arc length between the electrodes is 24 mm. Wall loading is 31.3 W/cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 2.2 mg Hg and 15 mg total of metal halides PrI3, CeI3 and NaI in molar ratios of PrI3:CeI3:NaI=0.8:1:19.69. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.55 cm3 and the arc length between the electrodes is 24 mm. Wall loading is 31.3 W/Cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
The quantities of active materials provided in the discharge region contained within arc discharge chamber 20 were 2.2 mg Hg and 15 mg total of metal halides PrI3, CeI3 and NaI in molar ratios of PrI3:CeI3:NaI=2:1:31.5. Xe gas was provided in this region at a pressure of about 330 mbar at room temperature. The volume of discharge chamber 20 is 0.55 cm3 and the arc length between the electrodes is 24 mm. Wall loading is 31.3 W/Cm2 at 150 W. Lamp photometry results are shown in Table 1 below.
In reducing the operating power of the lamps of the above examples to half, the emitted light remained substantially white without a greenish hue. Such color was satisfactory to the eye for general illumination uses and it was substantially impossible to discern any color or hue change under such dimmed conditions. Thus, the lamps of the present invention remain at the same CCT and are substantially constant in terms of hue throughout the dimming range, and further, they have higher lumen efficacy compared to the standard lamps at rated power.
Such dimming of lamps of the present invention from full power during operation is accomplished through operating the lamps in an electronic ballast circuit, a well known version of which, 40, is shown in block diagram form in FIG. 11. The electrical power for the circuit and lamp is drawn from a conventional 60 Hertz alternating current source which supplies such current at a fixed voltage to a power factor correction and electromagnetic interference filter circuit portion, 41. This circuit portion converts the alternating polarity line voltage to a constant polarity voltage of a value significantly greater than the peak line voltage while maintaining a sinusoidal current that is in phase with the line voltage, and limits electromagnetic emissions in doing so.
This constant polarity voltage is supplied as the input voltage to a buck voltage converter or regulator, 42, which in turn provides a regulated constant polarity voltage and current output. This voltage output is reduced in magnitude from the constant polarity input voltage provided to the regulator to a value set by an internal reference, but the regulator also provides the full value of that input voltage at its output during initiation of lamp operation prior to the striking of an arc therein. Changing the value of the regulator internal reference permits changing the current supplied to the lamp being operated to thereby allow selective dimming of that lamp. The constant polarity output voltage of the regulator is changed to a low frequency square wave by an output bridge converter, 43, that is provided to an igniter, 44, that generates 4 kV starting voltage pulses for striking an arc in the lamp, 45, connected to its output while providing a square wave voltage supply to the lamp thereafter.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scope of the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 20030141826 A1 | Jul 2003 | US |
