WO2011092627A1

WO2011092627A1 - High-efficiency and energy saving ceramic metal halide lamp

Info

Publication number: WO2011092627A1
Application number: PCT/IB2011/050325
Authority: WO
Inventors: Junming Tu; Jay Palmer; Gregory Golding; Thomas Graig Steere
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2010-01-28
Filing date: 2011-01-25
Publication date: 2011-08-04
Anticipated expiration: 2012-07-28
Also published as: TW201140644A

Abstract

A ceramic metal halide (CMH) lamp (400) is designed to operate at a lower-than-nominal lamp voltage (340) when driven by a conventionally HPS ballast (480), thereby substantially reducing (335) the lamp power consumption (350). The lower-than-nominal lamp voltage (340) is achieved by providing an appropriate combination of lamp design parameters, such as mercury and salt doses, arc length, and so on. The lamp (400) includes a high aspect ratio (between 4: 1 and 6: 1) discharge chamber (420) with a wall loading higher than 38 W/cm2. The high aspect ratio provides for a narrower arc width, and improved optical performance than a lower aspect ratio discharge chamber in standard HPS fixtures, and requires less mercury. The ionizable salt includes sodium iodide at over 50 mol% and rare earth iodides below 6 mol% to reduce arc bending and color separation, and to obtain high luminance efficacy and eliminate the need for protective sleeves about the discharge vessel.

Description

HIGH-EFFICIENCY AND ENERGY-SAVING

CERAMIC METAL HALIDE LAMP

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] This invention relates to the field of lighting, and in particular to an energy efficient ceramic metal halide (CMH) lamp that is suitable as a direct replacement for a conventional high pressure sodium (HPS) lamp, without modification to the ballast.

[0002] It is estimated that approximately 22% of the electrical energy consumed in the United States is used for lighting, and a significant amount of this lighting is provided for public and industrial applications. Due to their relatively high efficiency, high pressure sodium (HPS) lamps are often used in street and roadway lights, factory and warehouse lights, and other environments requiring a high luminance output per lamp.

[0003] The American National Standard Lighting Group - NEMA has published ANSI standard ANSI C78.42-2004 for standard HPS lamps, which defines the physical and electrical requirements for the HPS lamps to assure compatibility with standard HPS fixtures and ballasts. The standard establishes limits for the physical size of the lamps, as well as the electrical limits of the lamps when driven by standard ballasts. Of particular interest are the standard lamps in the range of 200-600 watts, as these are the lamps most often used for public and industrial applications. The most popular bulb/outer envelope in this range of wattages is an El 8 bulb, which has an elongated, generally cylindrical shape.

[0004] Ceramic metal halide (CMH) lamps are increasingly being used to replace conventional HPS lamps, primarily because they produce a whiter light than the yellow light produced by HPS lamps. U.S. patent 6,833,677, "150W-1000W MASTERCOLOR CERAMIC METAL HALIDE LAMP SERIES WITH COLOR TEMPERATURE ABOUT 4000k FOR HIGH PRESSURE SODIUM OR QUARTZ METAL HALIDE RETROFIT APPLICATIONS", issued 21 December 2004 to Jackson et al., discloses a lamp that is suitable for direct replacement (retrofit) of conventional high pressure sodium lamps, and is incorporated by reference herein. Although this CMH lamp has a lower efficacy than the convention HPS lamp it is designed to replace (85-95 lumens/watt compared to 110-125 lumens/watt for a HPS lamp), the illumination is perceived to be better, due to the higher color temperature and higher color rendering index (CRI) associated with CMH lamps (3500-4500K compared to 2000-3000K for a HPS lamp; CRI over 70 compared to below 40 for a HPS lamp).

[0005] Research has shown that color recognition and facial recognition are substantially improved when illumination is provided by CMH lamps compared to HPS lamps. By designing CMH lamps to conform to the ANSI standard for HPS lamps, these higher color temperature and higher color rendering index lamps can be provided as a direct replacement/retrofit lamps, using existing fixtures FIGs. 1A-1B and 1C-1D illustrate the difference in illumination provided by CMH lamps (FIGs. IB and ID), compared to HPS lamps (FIGS. 1 A and 1C). Although these figures are a grey-scale reproduction of a set of color photos, it is apparent that the whiter light produced by CMH lamps allows for distinguishing finer details.

[0006] A higher efficiency CMH lamp is disclosed in WO2008/129466, "METAL HALIDE LAMP COMPRISING A SHAPED CERAMIC DISCHARGE VESSEL", published 30 October 2008 for van der Eyden et al., and incorporated by reference herein. This lamp has a spheroidlike shape, providing a low aspect-ratio between the distance between electrodes and diameter of the discharge chamber, and an efficacy in the same range as the conventional HPS lamps (1 10- 125 lumens/watt). However, due to its spherical shape, some optical inefficiency is introduced when the lamp is used in HPS fixtures that are designed to accommodate the conventional elongated-cylinder shape of HPS lamps. Additionally, the spherical shape is costly to manufacture, and often requires the use of a protective quartz shroud when used in an open HPS fixture.

[0007] U.S. published application 2006/0164017, "CERAMIC HALIDE LAMP", published 27 July 2006 for Rintamaki et al., discloses a cylindrical lamp that provides up to 110 lumens/watt, and is incorporated by reference herein. This lamp has a preferred aspect ratio of between 2 and 3 and correspondingly requires a fairly high amount of mercury to assure proper lamp voltage. Accordingly, it will likely require the use of a protective quartz shroud when operated in open HPS fixtures, due to high mercury pressure. Additionally, the amount of rare- earth iodide is relative high (9-22 mol%), which is likely to cause arc bending, reducing the operating life of the lamp. . [0008] U.S. published application 2009/0001887, "METAL HALIDE LAMP AND

LIGHTING UNIT UTILIZING THE SAME", published 1 January 2009 for Takeuchi et al, discloses that high efficacy can be achieved using a discharge tube with an aspect ratio greater than 4, and is incorporated by reference herein. However, due to its narrow diameter and longer arc length, the lamp requires 4kV startup pulses at 240-390kHz, and would not be suitable for retrofitting conventional HPS fixtures with magnetic ballasts that operate at line frequency (50- 60Hz). A high amount of rare-earth iodide can also cause color separation when the lamp is mounted vertically, as the heavier iodides settle to the lower part of the lamp.

[0009] U.S. patent 6,555,962, "CERAMIC HALIDE LAMP HAVING MEDIUM ASPECT RATIO", issued 29 April 2003 to Jackson et al. discloses a lamp with an aspect ratio between 3 and 5, and is incorporated by reference herein. This lamp also uses a relatively high amount of rare-earth iodide, with the aforementioned accompanying potential arc bending and color separation problems. The efficacy of this lamp is below 100, but the color temperature is high (>4000K), thereby providing a higher perceived illumination, as discussed above.

[0010] Because of the substantially improved illumination characteristics, CMH lamps of lower wattage can be used in lieu of HPS lamps of higher wattage, yet still provide the same level of illumination. However, such a change would require the use of a different ballast, and would generally only be suitable for new construction due to the costs of replacing or modifying existing fixtures. For retrofit applications, the replacement of HPS lamps with CMH lamps results in better illumination, but does not provide any power savings.

[0011] It would be advantageous to provide a lamp that conforms to the aforementioned ANSI standard for HPS lamps in the 200-600 watt range, yet consumes significantly less wattage than the nominal wattage available from the corresponding standard ballasts. It would also be advantageous if such a lamp were designed to operate at this lower wattage without requiring any modification to the existing fixtures and ballasts, thereby allowing for a simple lamp-for- lamp replacement to achieve these significantly lower levels of power consumption. It would also be advantageous if these energy-efficient lamps were not significantly more expensive to produce, and if these lamps provided the same, or better, luminance as conventional full-wattage CMH replacements. It would also be advantageous if these energy-efficient lamps provided this luminance at a color temperature of about 4200K. It would also be advantageous if these energy- efficient lamps have a long operating life. [0012] These advantages, and others, can be realized by a CMH lamp that is designed to operate at a lower-than-nominal lamp voltage when driven by a conventionally HPS ballast, thereby substantially reducing the lamp power consumption, typically providing a 10-15% decrease in power consumption. The lower-than-nominal lamp voltage is achieved by providing an appropriate combination of lamp design parameters, such as mercury and salt doses, arc length, and so on. To provide the same or better illumination output as conventional full-wattage CMH lamp, the self absorption of additives including sodium and thallium is optimized within a certain range and the arc width is narrower than conventional metal halide lamps with a low aspect ratio discharge tube. This is realized by using a high aspect ratio discharge tube and a relatively small diameter discharge tube with a wall loading higher than 38 W/cm². The aspect ratio (the ratio between the inner length and inner diameter of the vessel) is between 4 and 6. The high aspect ratio provides for improved optical performance in standard HPS fixtures, and eliminates the need for a protective sleeve for open fixture operation. The sodium iodide is preferably over 50 mol% to reduce arc bending and obtain high lumens. Other iodides are added to achieve a color temperature of 4200K. To avoid the color segregation that is typical of a high aspect ratio discharge vessel, the rare earth iodides are preferably less than 6 mol%.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:

FIGs. 1 A-1D illustrate differences between the light produced by HPS lamps and CMH lamps in a retrofit application.

FIGs. 2A-2C illustrate example figures from ANSI C78.42-2004, indicating physical and electrical limits for HPS lamps.

FIG. 3 illustrates an example set of ANSI C78.42-2004 limits for the operation of the lamp when driven by a standard ballast.

FIG. 4 illustrates an example embodiment of a lamp in accordance with this invention.

[0014] Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention. DETAILED DESCRIPTION

[0015] In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the Figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0016] FIGs. 2A-2C illustrate example figures from ANSI Standard C78.42-2004O. In FIG. 2A, the physical limits of an El 8 bulb are illustrated. In FIGs. 2B and 2C, the operating limits of a 200W and 400W HPS lamp are illustrated, respectively. Of particular note, the standard calls for an HPS lamp to operate at a nominal operating point (210, 210' in FIG. 2) of voltage and wattage; for example, the 200W HPS lamp is specified as a "200- Watt 100- Volt S66 HPS lamp", "200-Watt" specifying the nominal wattage (reference 230 in FIG. 2B), and "100- Volt" specifying the nominal voltage (reference 220 in FIG. 2B). In like manner, the "400-Watt 100- Volt S51 HPS lamp" has a nominal wattage (230') of 400 watts at a nominal voltage (220') of 100 volts". This nominal operating point 210, 210' is defined with respect to a nominal HPS ballast having a characteristic curve 260, 260', as detailed further below.

[0017] This invention is presented using the paradigm of a ceramic halide lamp that conforms to the ANSI Standard C78.42-2004 "400-Watt 100-Volt S51 HPS lamp" specification, for ease of reference and understanding. One of skill in the art will recognize that the principles presented herein are applicable for other HPS lamp specifications as well, and particularly well suited for lamps in the 200W-600W range. Also for ease of reference, the terms HPS lamp and HPS ballast are used herein to refer to lamps and ballasts that conform to ANSI Standard C78.42-2004. Unless otherwise stated, the electrical characteristics of an HPS ballast is assumed to conform to the "ballast characteristic curve" illustrated in the ANSI Standard C78.42-2004 lamp specifications, as detailed further below. [0018] As noted above, a variety of designs of ceramic metal halide lamps exist that are suitable for retrofitting conventional HPS fixtures. However, they exhibit one or more of the following shortcomings: relatively high mol% of rare-earth iodides, relatively low efficacy, relatively high manufacturing costs, and relatively poorer optical efficiency. Additionally, even though the perceived illumination provided by these lamps is higher than conventional HPS lamps, they do not allow for reduced power consumption in retrofit applications using existing HPS ballasts.

[0019] To achieve an energy savings using existing HPS ballasts, the lamp of this invention is designed to operate at lower-than-nominal lamp voltage. Conventionally, lamps are designed to operate at the specified nominal lamp voltage, with manufacturing and age variances expected to occur about this nominal lamp voltage. That is, as the term 'design lamp voltage' is used herein, it is the voltage about which the distribution of lamp voltages from the population of produced lamps will vary. Alternatively stated, the design lamp voltage is the lamp voltage at which an ideally manufactured lamp is expected to operate after some defined break-in period in a defined environment, differences from the design lamp voltage being attributed to

manufacturing and other anomalies. In accordance with ANSI Standard C78.42-2004, the break- in period is defined as 100 hours, the environment including operating the lamp using a ballast having nominal characteristics at an ambient temperature of 25°C +/- 5°C.

[0020] FIG. 3 illustrates an example set of lamp operating limits as defined in ANSI Standard C78.42-2004. The curve 360 is a characteristic curve of a HPS ballast that provides a nominal wattage 330 at a nominal voltage 320, representative of the characteristic curves 260, 260' of FIGs. 2B and 2C for the standard 200W and 400W HPS ballasts. In the case of the 400- Watt 100- Volt S51 HPS lamp, the nominal wattage is 400W at a nominal voltage of 100V, as illustrated at 220', 230' of FIG. 2C. Conventionally, using techniques well known in the art, the lamp design parameters, such as arc length, mercury and salt dosages, the size and shape of the discharge chamber, and so on, are arranged such that the lamp operates at this nominal voltage when driven by an 'ideal' ballast that exhibits the illustrated characteristic curve 360.

Additionally, the manufacturing processes are controlled to assure that the variance among lamps does not exceed the specified limits 362, 364, 366, 368 over the expected life of the lamp. In so doing, each manufactured lamp can be expected to work properly in any fixture using any ballast that conforms to the corresponding HPS standard. [0021] As also illustrated in FIG. 3, if the lamp is operating at a lower-than-nominal voltage 340, the HPS ballast will provide less-than-nominal wattage 350 to the lamp. Alternatively stated, if a lamp's design parameters are adjusted such that the lamp operates at this lower-than- nominal voltage, it will consume fewer watts when driven by a standard HPS ballast that provides the nominal wattage to a lamp that is designed to operate at the nominal volts. One of skill in the art will recognize that although the illustrated ballast characteristic curve 360 represents the voltage-wattage relationship of a nominal HPS ballast, the characteristic curve associated with any particular ballast will have the same general shape as curve 360, albeit offset with respect to curve 360. Accordingly, a similar energy-savings will be achieved by operating the lamp at a lower-than-nominal voltage, regardless of the particular HPS ballast that is driving the lamp.

[0022] In accordance with an aspect of this invention, the lamp is purposely designed to cause it to operate at a lower-than-nominal voltage when driven by an ANSI Standard C78.42- 2004 HPS ballast. As can be seen in FIG. 3, the voltage-wattage relationship about the nominal lamp voltage is substantially linear, and for this region, the following relationship applies:

Lamp Voltage = Lamp Output Wattage/(Lamp Current * Power Factor).

[0023] As noted above, the lamp voltage that is provided by an HPS ballast is dependent upon a variety of design parameters; these parameters, including the amount of mercury, the amount of iodides, the spacing of the electrodes, the shape and size of the discharge chamber, and others, determine the amount of current that flows through the lamp, as well as the power factor, thereby controlling the lamp voltage for a given/desired lamp output wattage.

[0024] For optimal optic efficiency, noting that the standard HPS lamps are somewhat elongated, as illustrated in FIG. 2A, and existing HPS fixtures are generally designed to optimize the light provided by such elongated lamps, the lamp of this invention is preferably designed to have a high aspect ratio, thereby having a substantially longer length than diameter. As is common in the art, and as defined herein, the aspect ratio of a lamp is defined as the ratio of the distance (E) between the electrode tips within a discharge chamber divided by the interior diameter (D) of the discharge chamber, where the diameter (D) of the chamber is defined as the longest line segment extending across the chamber substantially orthogonal to a line extending between the electrode tips. [0025] As also noted above, an objective of this invention is to provide an energy-saving lamp that can be produced at a reasonable cost. Accordingly, the lamp is preferably cylindrically shaped, formed by an extrusion process, to reduce manufacturing costs, and preferably includes a relatively small proportion of mercury, to avoid the need to provide a protective shell. Reducing the amount of mercury also has the desired effect of reducing the lamp voltage when driven by a standard HPS ballast. Additionally, a high aspect ratio also reduces the amount of mercury required to sustain operation.

[0026] In a preferred embodiment, the lamp is preferably designed to have a discharge chamber with a relatively large diameter, to improve the ease of starting the lamp. This also provides an advantage of reducing the surface temperature of the discharge chamber by increasing the distance between the chamber wall and the discharge arc.

[0027] However, given that a high aspect ratio is desirable to reduce the required mercury content, a high aspect ratio will also result in a long arc length, with a corresponding increase in the difficulty of starting the lamp. Color separation is also more prominent when the aspect ratio is very high. Therefore, in a preferred embodiment of this invention, the aspect ratio is preferably above 4: 1 , but also below 6: 1 , to satisfy these conflicting requirements.

[0028] The illumination efficacy of a lamp generally increases with lamp wall loading, up to a point; however, a very high wall loading (above 60W/cm²) should be avoided, to prevent high wall temperature and excessive corrosion, which generally leads to a short operational life. Lamp wall loading is defined as the lamp wattage divided by the chamber's interior surface area in the region of the arc; for example, in a cylindrical chamber, the surface area is defined as the inner circumference of the cylinder multiplied by the arc length.

[0029] Although rare-earth iodides generally provide for a high illumination output, the use of a significant amount of rare-earth iodides will lead to arc bending and color separations, as discussed above. Rare-earth iodides are used in conventional CMH lamps to provide a high color rendering index (CRI), and are generally preferred when accurate color rendering is required. However, most HPS lamps in the 200-600W range are deployed for public/roadway lighting, warehouse lighting, and similar applications, where the accurate rendering of color is not a high- priority requirement. In a preferred embodiment of this invention, the amount of rare-earth iodides is relatively slight, thereby avoiding the aforementioned arc bending and color separation problems, as well as reducing manufacturing costs, even though the color rendering

characteristics may be less than optimal.

[0030] Sodium iodide ( al) provides fairly good illumination, and has the advantage that it does not generally cause arc bending, and, as a lighter iodide, is not subject to color separation regardless of the orientation of the lamp. To provide a variety of colors and color temperatures, any of a variety of Cal₂, Cel₃, Til, Lil, Csl, Mgl₂, Mnl₂, and Inl combinations may also be included; however, as noted above, the amount of rare-earth iodides (Cel₃) is preferably slight. By using a high aspect ratio, the arc width is reduced, thereby reducing the Na and Tl self- absorption and maximizing their contributions to lumens.

[0031] Given the above constraints and limitations, a lamp in accordance with this invention preferably includes a discharge chamber that has an aspect ratio between 4: 1 and 6: 1, and is filled with an ionizable salt and mercury combination that causes the lamp to operate with a wall loading between 38 and 60 W/cm , at a lamp voltage that is substantially less than the nominal lamp voltage when driven by a standard HPS ballast, wherein the ionizable salt includes a rare- earth iodide at less than 5 mol%, sodium iodide (Nal) at over 50 mol%, and one or more of Cal₂, Cel₃, Til, Lil, Csl, Mgl₂, Mnl₂, and Inl. In particular, a wall loading above 40 W/cm and a concentration of sodium iodide over 70 mol% is preferred. In a preferred embodiment, the decrease in lamp voltage (325 in FIG. 3) is at least 10%, and preferably at least 15%. This reduction 325 will generally provide a reduction 335 in lamp wattage of about 10-15%. [0032] Applying these constraints, consider, for example, the physical design of a lamp such as illustrated in FIG. 3 that is intended to replace a 400W HPS lamp, yet consume only 350 watts when driven by a standard HPS ballast. The lamp 400 includes a base 440, an outer envelope 410 with a discharge vessel 420 within. The base 440 is configured to support the outer envelope 410 and the ceramic discharge vessel 420 and includes external terminals 442 for coupling a HPS ballast 480 to the electrodes 430 of the discharge vessel 420. Preferably, the base 440 and outer envelope 410 conform to ANSI standard C78.42-2004, to assure physical compatibility for retrofitting HPS fixtures with this lamp.

[0033] As noted above, the aspect ratio (E/D) of the chamber of the vessel 420 should be between 4: 1 and 6: 1 , and the shape of the discharge vessel 420 is preferably cylindrical shape made by an extrusion process to reduce manufacturing costs. In this example, assume a desired 5: 1 aspect ratio, and a 50 W/cm² wall loading.

[0034] To achieve a 50 W/cm² wall loading while consuming 350 watts, the chamber surface area should be 7 cm², or 700 mm². If the internal diameter is D, and the distance between electrode tips 432 (arc length) is E, an aspect ratio of 5: 1 indicates that E=5*D. The required surface area of 700 mm² is equal to pi*D*E, or pi*5*D². Accordingly, in this example, the diameter of the discharge chamber to achieve a 50 W/cm² wall loading with an aspect ratio of 5: 1 should be about 6.6 mm (sqrt(700/pi*5)), with a corresponding arc length of 33 mm.

[0035] Given these physical dimensions of the chamber, the appropriate amount of mercury to assure proper startup can be determined using techniques common in the art. In a typical embodiment for such a chamber, the amount of mercury will be about 5- 10 mg, depending upon the amounts of sodium iodide and other salts. Accordingly, given this low amount of mercury, and cylindrical shape, the conventional protective shroud is not required; instead, a molybdenum coil 450 is wrapped around the discharge vessel 420, to limit the likelihood of a rupture in the vessel 420 causing a rupture of the outer envelope 410, and/or limiting the effects of such a rupture to the outer envelope 410.

[0036] In combination with the amount of mercury, the amounts and proportions of salts are determined so as to cause the lamp to operate at a lower-than-nominal voltage when driven by a standard HPS ballast, thereby providing, in the above example, the desired 350 watt

consumption by the lamp. [0037] Two example embodiments are provided, each suitable to replace a 400W HPS lamp in a standard HPS fixture with standard ballast. The first embodiment provides the advantages of low mercury and rare-earth iodides and high illumination efficacy, and operates at the nominal lamp voltage of 100 volts when driven by a standard ballast, and consumes a nominal 400W when so driven. The second embodiment uses the same physical arrangement, but operates at a less-than-nominal voltage of about 85 volts when driven by the same standard ballast, and corresponding consumes approximately 10% less power (360W).

[0038] In each example, the cylindrical discharge chamber comprises polycrystalline alumna (PCA), with a wall thickness of 1.3mm, an internal diameter (D) of 7.5mm, and an electrode spacing (E) of 33mm (aspect ratio of 4.4: 1). The fill gas is Xe with a trace of Kr85 at a pressure of 100 mbar.

[0039] In these examples, less than l Omg of mercury is used; preferably, the ratio of the weight of salt to the weight of mercury is in the order of 4: 1 to 7: 1. The color temperature of the first example is approximately 3000K, and in the second example, approximately 4200K. In each of these examples, the luminance efficacy is over 1 10 lumens per watt, which, when coupled with the higher color temperature, provides a significant illumination advantage over the HPS lamps being replaced. [0040] The foregoing merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope. For example, although the discharge vessel is preferably cylindrical, to allow it to be manufactured using a low cost extrusion process, the principles of this invention are not limited to cylindrical discharge vessels, and may be preferred for reasons other than cost. If, for example, the diameter of the discharge chamber narrowed toward the electrode tips, a higher vapor pressure, and therefore more lumens, will be produced because of the higher temperature of the metal iodides near the tips. Additionally, if the diameter of the vessel is minimized in regions beyond the discharge region, the reduction in external surface area will provide a corresponding reduction in heat loss. In like manner, it has been found that a 'cigar-shaped' discharge vessel provides a more uniform heat distribution and less thermal stress. These and other system configuration and optimization features will be evident to one of ordinary skill in the art in view of this disclosure, and are included within the scope of the following claims.

[0041] In interpreting these claims, it should be understood that:

a) the word "comprising" does not exclude the presence of other elements or acts than those listed in a given claim;

b) the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several "means" may be represented by the same item or hardware or software implemented structure or function;

e) each of the disclosed elements may be comprised of hardware portions (e.g., including discrete and integrated electronic circuitry), software portions (e.g., computer programming), and any combination thereof;

f) hardware portions may include a processor, and software portions may be stored on a computer-readable medium, and may be configured to cause the processor to perform some or all of the functions of one or more of the disclosed elements;

g) hardware portions may be comprised of one or both of analog and digital portions; h) any of the disclosed devices or portions thereof may be combined together or separated into further portions unless specifically stated otherwise;

i) no specific sequence of acts is intended to be required unless specifically indicated; and j) the term "plurality of an element includes two or more of the claimed element, and does not imply any particular range of number of elements; that is, a plurality of elements can be as few as two elements, and can include an immeasurable number of elements.

Claims

CLAIMS We claim:

1. A ceramic metal halide lamp (400) comprising:

a ceramic discharge vessel (420) that encloses a chamber of diameter D and includes a pair of electrodes (430) having electrode tips (432) that are spaced apart by a distance E in the discharge vessel (420), having an aspect ratio of distance: diameter (E:D) of at least 4: 1 ,

an outer envelope (410), and

a base (440) that is configured to support the outer envelope (410) and the ceramic discharge vessel (420) and includes external terminals (442) for coupling a ballast (480) to the pair of electrodes (430),

wherein:

the chamber is filled with a combination that includes an ionizable salt and mercury that causes the lamp to operate with a wall loading of between 38 W/cm² and 60 W/cm²,

the ionizable salt includes sodium iodide (Nal) at over 50 mol%, a rare-earth iodide at less than 7 mol%, and one or more of Cal₂, Til, Lil, Csl, Mgl₂, Mnl₂, and Inl.

2. The lamp of claim 1, wherein the lamp (400) is suitable for use with an HPS ballast (480) that provides a nominal lamp voltage (320) in accordance with ANSI standard C78.42-2004, and the combination of ionizable salt and mercury causes the lamp (400) to operate at a lamp voltage (340) that is substantially less than the nominal lamp voltage (320) when driven by the ballast (480), thereby consuming substantially less power (350) than a nominal lamp wattage (330) associated with the ballast (480).

3. The lamp of claim 1 , wherein the aspect ratio is not greater than 6: 1.

4. The lamp of claim 1, wherein the lamp voltage (340) is at least 10% lower than a nominal lamp voltage (320).

5. The lamp of claim 1, wherein the diameter D is at least 7mm.

6. The lamp of claim 1, wherein the combination includes less than lOmg of mercury.

7. The lamp of claim 1, wherein the ceramic discharge vessel (420) is substantially cylindrical.

8. The lamp of claim 1, wherein the combination includes sodium iodide at over 70 mol%.

9. The lamp of claim 1, wherein the wall loading is between 40 W/cm² and 60 W/cm².

10. The lamp of claim 1, wherein the combination includes an inert fill gas, with a fill pressure below 200 mbar.

11. The lamp of claim 1, wherein the lamp (400) consumes at least 10% less power (355) than the nominal lamp wattage (330).

12. The lamp of claim 1, wherein the combination includes Til at between 0.5 mol% and 2.5 mol%.

13. The lamp of claim 12, wherein the combination includes Cal₂ at between 15 mol% and 30 mol%.

14. The lamp of claim 12, wherein the combination includes Cel₃ at between 1 mol% and 6 mol%.

15. The lamp of claim 1, wherein the combination includes Cel₃ at between 1 mol% and 6 mol%.

16. A lamp (400) that is suitable for use with a ballast (480) that provides a nominal lamp voltage (320) in accordance with ANSI standard C78.42-2004, comprising:

a ceramic discharge vessel (420) that encloses a chamber of diameter D and includes a pair of electrodes (430) having electrode tips (432) that are spaced apart by a distance E in the discharge vessel, having an aspect ratio of distance: diameter (E:D) of at least 4: 1,

an outer envelope (410), and a base (440) that is configured to support the outer envelope (410) and the ceramic discharge vessel (420) and includes external terminals (442) for coupling the ballast (480) to the pair of electrodes (430),

wherein:

the base (440) and outer envelope (410) conform to ANSI standard C78.42-2004, and the chamber is filled with a combination that includes an ionizable salt and mercury that causes the lamp (400) to operate at a lamp voltage (340) that is substantially less than the nominal lamp voltage (320) when driven by the ballast (480), thereby consuming substantially less power (350) than a nominal lamp wattage (330) associated with the ballast (480).

17. The lamp of claim 16, wherein the ionizable salt includes Nal of at least 50 mol% and rare- earth iodides of less than 7 mol%.

18. The lamp of claim 17, wherein a ratio of weights of the iodized salt and mercury is at least 4: 1.

19. The lamp of claim 17, wherein the combination of ionizable salt and mercury causes the lamp to operate with a wall loading of between 38 W/cm² and 60 W/cm².

20. A method of manufacturing a lamp (400) that is suitable for use with a ballast (480) that provides a nominal lamp voltage (320) in accordance with ANSI standard C78.42-2004, comprising:

forming a ceramic discharge vessel (420) that encloses a chamber of diameter D and includes a pair of electrodes (430) having electrode tips (432) that are spaced apart by a distance E in the discharge vessel, having an aspect ratio of distance: diameter (E:D) of at least 4: 1, filling the ceramic discharge vessel (420) with a combination that includes an ionizable salt and mercury, the ionizable salt including Nal at over 50 mol% and rare-earth iodides at less than 7%,

providing an outer envelope (410) for enclosing the ceramic discharge vessel (420), and mounting the outer envelope (410) and ceramic discharge vessel (420) on a base (440) that includes external terminals (442) for coupling the ballast (480) to the pair of electrodes

(430);

wherein:

the base (420) and outer envelope (410) conform to ANSI standard C78.42-2004, and the combination of ionizable salt and mercury is formed to cause the lamp to operate at a lamp voltage (340) that is substantially less than the nominal lamp voltage (320) when driven by the ballast (480), thereby consuming substantially less power (350) than a nominal lamp wattage (330) associated with the ballast (480).