WO2011121492A2

WO2011121492A2 - Metal halide lamp

Info

Publication number: WO2011121492A2
Application number: PCT/IB2011/051223
Authority: WO
Inventors: Piet Antonis; Anna Wilhelmina Maria Wondergem-De Best; Peter Arend Seinen; Joris Hubertus Antonius Hagelaar; Wilhelmus Johannes Jacobus Welters; Marinus Cornelis Raas
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-04-02
Filing date: 2011-03-23
Publication date: 2011-10-06
Also published as: WO2011121492A3

Abstract

The invention relates to a metal halide lamp (1) comprising a ceramic discharge vessel, having an inner diameter, enclosing a discharge space which accommodate two electrodes arranged at an electrode distance, and which contains a noble gas and a salt filling, wherein (1) the salt filling comprises an alkali halide, a rare earth halide, and optionally thallium halide; (2) the discharge vessel has an aspect ratio, defined as the electrode distance divided by the inner diameter, of at maximum 4; and (3) the metal halide lamp has a wall load at full power, defined as the lamp power divided by the inner surface area of the discharge space, of at least 25 W/cm². Especially, the discharge space contains 0.015-1.5 μg/mm³ alkali halide.

Description

Metal halide lamp

FIELD OF THE INVENTION

The invention relates to a metal halide lamp.

BACKGROUND OF THE INVENTION

Metal halide lamps are known in the art. Such lamps operate under high pressure and comprise ionizable gas fillings of, for example, Nal (sodium iodide), Tll (thallium iodide), Cal₂ (calcium iodide), and/or REI_n. REI_n refers to rare earth iodides.

Characteristic rare earth iodides for metal halide lamps are Cel₃, Prl₃, Ndl₃, Dyl₃, and Lul₃. An important class of metal halide lamps is formed by ceramic discharge metal halide lamps (CDM-lamps).

WO05088675 for instance discloses a metal halide lamp comprising a discharge vessel surrounded, with a clearance, by an outer envelope and having a ceramic wall which encloses a discharge space filled with a filling comprising an inert gas, such as xenon (Xe), and an ionizable salt, wherein, in said discharge space, two electrodes are arranged whose tips have a mutual interspacing so as to define a discharge path between them, with the special feature that said ionizable salt comprises Nal, Tll, Cal₂ and X-iodide, wherein X is selected from the group comprising rare earth metals. In a specific embodiment of WO05088675, X is one or more elements selected from the group comprising Ce, Pr, and Nd.

SUMMARY OF THE INVENTION

Dimming becomes more and more important in lighting applications for several reasons (environmental, TCO (total cost of ownership), and scene setting).

A drawback of conventional metal halide lamps is that they may not or hardly be dimmable without loss of light technical properties. Furthermore, halogen lamps dim according to the blackbody line towards lower color temperatures (i.e. towards the red). Conventional ceramic metal halide lamps, however, dim typically towards the green.

Hence, it is an aspect of the invention to provide an alternative metal halide lamp, which preferably further obviates one or more of the above-described drawbacks. It is especially an aspect of the invention to provide an alternative metal halide lamp which has a stable discharge and/or which is dimmable substantially along the black body locus (or black body line), briefly indicated as BBL.

In an aspect, the invention provides a metal halide lamp comprising a ceramic discharge vessel, having an inner diameter, enclosing a discharge space (or discharge volume) which accommodates (at least) two electrodes, (the at least two electrodes) being arranged at an electrode distance, and which (discharge space) contains a noble gas and a salt filling, wherein:

the salt filling comprises an alkali halide, a rare earth halide, and optionally thallium halide; preferably the discharge space contains 0.015-1.5 μg/mm³ alkali halide (especially iodide), more particularly 0.02-1.1 μg/mm³ alkali halide (especially iodide),

the discharge vessel has an aspect ratio, defined as the electrode distance divided by the inner diameter, of at maximum 4; and

the metal halide lamp has a wall load at full power, defined as the lamp power divided by the inner surface area of the discharge space, of at least 25 W/cm².

In another aspect, the invention provides a metal halide lamp comprising a ceramic discharge vessel, having an inner diameter, enclosing a discharge space (or discharge volume) which accommodates (at least) two electrodes, (the at least two electrodes being) arranged at an electrode distance, and which (discharge space) contains a noble gas and a salt filling, wherein the salt filling comprises an alkali halide, a rare earth halide, and thallium halide, more particularly an alkali iodide, a rare earth iodide, and thallium iodide, wherein preferably the discharge space contains 0.015-1.5 μg/mm³ alkali halide (especially iodide), more particularly 0.02-1.1 μg/mm³ alkali halide (especially iodide).

The invention may enable dimming of metal halide high intensity discharge (HID) lamps, while maintaining good light technical properties. Compared to conventional ceramic metal halide lamps, the strong color shift, typically towards the green, may be reduced and/or may behave more naturally during dimming, i.e. more like incandescent and halogen lamps. Further, the drop in color rendering may be reduced as well as the drop in efficacy.

The invention may provide a well-dimmable metal halide lamp, especially characterized by a constant color, typically less than 10 SDCM (standard deviation of color matching) shift (while dimming) or a color point shift toward lower temperatures parallel to the BBL (like incandescent or halogen lamps), which may be combined with a red-green shift of typically less than +/- 0.02 points, especially less than +/- 0.010 points. In an embodiment, the aspect ratio is in the range of 0.5-4, more especially the aspect ratio may be in the range of 0.5-2. This may give the best results.

The wall load is preferably at least 25 W/cm², more preferably at least 30 W/cm². In a specific embodiment, the wall load is in the range of 25-50 W/cm², more particularly in the range of 30-50 W/cm². The wall load is defined as the lamp power divided by the inner surface area of the discharge space, wherein the lamp power is the full power or nominal power of the lamp (i.e. the power rating of the lamp).

Especially, the alkali halide comprises one or more of sodium halide (NaT) and lithium halide (Lil). Hence, in an embodiment, the discharge space comprises sodium halide (especially sodium iodide) and/or lithium halide (especially lithium iodide). The phrase "the alkali halide comprises one or more of sodium halide and lithium halide" does not exclude the presence of other halides (other than alkali halides), see also below.

In an embodiment, the discharge space contains 0.015-1.5 μg/mm³ alkali halide, particularly alkali iodide, even more particularly 0.02-1.1 μg/mm³ alkali halide. Especially these contents may lead to discharge lamps which dim well with a stable color point or natural dimming behavior. Especially, the joint content of sodium iodide and lithium iodide is in the indicated ranges. For instance, the discharge space may contain 0.4 μg/mm³ sodium iodide and 0.4 μg/mm³ lithium iodide.

Even more especially, the discharge space contains 0.1-0.5 μg/mm³ sodium iodide (with optionally also lithium iodide, in such an amount that the total amount of alkali halides is not more than 1.5 μg/mm³, particularly not more than 1.1 μg/mm³). In another embodiment, the discharge space contains 0.1-0.8 μg/mm³ lithium iodide (with optionally also sodium iodide, in such an amount that the total amount of alkali halides is not more than 1.5 μg/mm³, particularly not more than 1.1 μg/mm³).

As mentioned above, the discharge space preferably also contains thallium iodide (Til) (as component of the salt filling).

The discharge space may also contain an alkaline earth halide and/or a transition metal halide (as component(s) of the salt filling). In embodiments, the terms "alkaline earth halide" and "transition metal halide" may also refer to a combination of two or more alkaline earth halides or transition metal halides, respectively. Especially, the discharge space may (further) contain magnesium halide, particularly magnesium iodide, and/or calcium halide, more particularly calcium iodide. Even more especially, the discharge space contains, in specific embodiments, (at least) calcium iodide (as an alkaline earth iodide). Further, the discharge space preferably also contains a rare earth halide (as component of the salt filling). Again, the term "rare earth halide" may, in an embodiment, also refer to a plurality of rare earth halides. Especially, the discharge space contains one or more of cerium iodide, neodymium iodide, praseodymium iodide, dysprosium iodide, ytterbium iodide and lanthanum iodide, even more especially iodides of one or more of Dy, Ce, Pr, and La. Especially, at least Ce iodide and/or Dy iodide are present. Hence, in an embodiment, the salt filling comprises at least one or more iodides selected from the group consisting of cerium, praseodymium and dysprosium iodide.

Hence, preferred embodiments comprise halides of (a) sodium and/or lithium, (b) thallium, and (c) cerium and/or dysprosium, especially iodides thereof (as components of the salt filling). In a further embodiment, the salt filling further comprises one or more iodides selected from the group consisting of Ca, Mg, Sc, Y, La, Pr, Sm, Eu, Gd, Tb, Ho, Tm, Lu, In, Sn and Zn.

The halides are preferably iodides.

As will be clear to the person skilled in the art, the discharge vessel may further contain mercury. As will also be clear to the person skilled in the art, the discharge vessel may further contain a noble gas, such as xenon and/or argon.

In a specific embodiment, the invention provides a metal halide lamp as defined above, wherein (la):

i. the rare earth halide content is between 0.008 and 0.1 μg/mm³, and wherein the rare earth halide comprises one or more halides selected from the group consisting of Ce, Pr, La, and Dy halides, and especially comprises at least Ce halide and/or Dy halide;

ii. the sodium halide content is between -0.02 +5 *RE halide (i.e. rare earth halide) and 0.10 +10*RE halide ^g/mm³];

iii. the Tl halide is between 0.75 * Na halide and Na halide +0.9 ^g/mm³]; iv. the salt filling further comprises one or more of Ca, Mg, Li halides, especially at least Ca halide and/or especially at least Li halide.

In a specific embodiment, the invention provides a metal halide lamp as defined above, wherein (lb):

i. the rare earth halide content is between 0.015μιηο1/αη³ and 0.2 μιηοΐ/cm³ and wherein the rare earth halide comprises one or more halides selected from the group consisting of Ce, Pr, La, and Dy halides, and especially comprises at least Ce halide and/or Dy halide; ii. the sodium halide content is between -0.13+17*RE halide and 0.67+37*RE halide [μιηοΐ/cm³];

iii. the Tl halide is between 0.35* Na halide and 0.45 * Na halide + 0.41

[μιηοΐ/cm³];

iv. the salt filling further comprises one or more of Ca, Mg, Li halides, especially at least Ca halide and/or especially at least Li halide.

Especially such lamps may show advantageous properties with respect to dimming. Further, in an embodiment, such metal halide lamps may have a color temperature, at nominal lamp power, in the range of 2500-3500 K.

In yet a further specific embodiment, the invention provides a metal halide lamp as defined above, wherein (2a):

i. the rare earth halide content is between 0.05 and 0.5 μg/mm³ and the rare earth halide comprises one or more halides selected from the group consisting of Dy, Ce, Pr, and La halides, and especially comprises at least Ce halide and/or Dy halide;

ii. the alkali halide content is between O.lxRE halide and lxRE halide ^g/mm³]; iii. the Tl halide content is at least 40% of the total mass of rare earth halides, alkali halides and Tl-halide.

In a specific embodiment, the invention provides a metal halide lamp as defined above, wherein (2b):

i. the rare earth halide content is between 0.1 and 1 μιηοΐ/cm³ and the rare earth halide comprises one or more halides selected from the group consisting of Dy, Ce, Pr, and La halides, and especially comprises at least Ce halide and/or Dy halide;

ii. the alkali halide content is between 0.35 * RE halide and 4.1 * RE halide

[μιηοΐ/cm³];

iii. the Tl halide content is at least 40% of the total mass of rare earth halides, alkali halides and Tl-halide.

Further, the salt fillings may additionally comprise one or more of Ca, Mg, Li halides, especially at least Ca halide and/or at least Li halide.

Especially, such lamps may show advantageous properties with respect to dimming. Further, in an embodiment, such metal halide lamps may have a color temperature at nominal lamp power in the range of 3500-5000 K.

The term "RE halide" in the above content formulas represents the total amount of RE halide (i.e. when different RE halides are present, the total weight or the total molar amount of all RE halides is taken). The discharge vessel of the metal halide lamp as defined herein may have a wall thickness in the range of 0.3 and about 1.2 mm.

According to this invention, dimmable systems may be realized that can be dimmed to typically a power level of 50% while still fulfilling the requirements for a well dimmable system. Especially, such lamps may have a stable and reproducible light output with stable and reproducible light and color properties.

The color shifts associated with the known art are often in the green direction, which is unfavorable for most applications.

In the description and claims, the expression "nominal power" is equivalent to the expression "full power". These expressions define the power for which the lamp is designed (rated) to operate and it is common practice that the said power is indicated on the lamp and/or its packaging.

In the description and claims, the expression "ceramic discharge vessel" is defined as a discharge vessel having a wall formed from ceramics. Ceramics are understood to be refractory material such as monocrystaline metal oxide, for example sapphire, gas-tight densely sintered translucent metal oxide like aluminum oxide (AI₂O₃), yttrium- aluminum garnet (YAG) or yttrium oxide (YOX), or gas-tight sintered translucent non-oxidic material like aluminum nitride (A1N).

Especially, the discharge vessel may comprise a side extension. This may be the remains of a side filling channel, which is used to fill the discharge space, and which is sealed thereafter. Hence, the invention also provides a discharge vessel comprising a closed side filling channel. In a specific embodiment, which may have advantageous properties, the electrodes are in electrically conductive contact with current lead-through conductors, and the current lead-through conductors are directly sintered in the discharge vessel (especially in the respective end plugs).

The term "white light" as used herein, is known to the person skilled in the art. It especially relates to light having a correlated color temperature between about 2000 and 20000 K, especially between 2700 and 20000 K, for general lighting especially in the range of about 2700 K and 6500 K, and for backlighting purposes especially in the range of about 7000 K and 20000 K, and especially within about 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about 10 SDCM from the BBL, even more especially within about 5 SDCM from the BBL.

Further, for specific applications, it may be desired to add other elements that may influence the optical properties of the metal halide lamp, especially with respect to color point and/or color rendering. Hence, in a further embodiment the salt filling further comprises one or more elements selected from the group consisting of Mg, Sc, Y, La, Pr, Sm, Eu, Gd, Tb, Ho, Tm, Lu, In, Sn and Zn.

The phrase "ionizable salt filling further comprises one or more elements..." especially indicates that iodides of such elements are comprised by the salt filling.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. 1 schematically depicts an embodiment of a lamp according to the invention in a side elevation;

Fig. 2 schematically depicts an embodiment of the discharge vessel of the lamp of Fig. 1 in more detail;

Fig. 3 schematically depicts an embodiment having an alternatively shaped discharge vessel;

Fig. 4 schematically depicts a further embodiment of the discharge vessel.

The Figures are not necessarily drawn to scale. Figures 1-4 are especially displayed to illustrate some basic principles of certain embodiments. However, the invention is not limited to the embodiments of discharge vessels schematically depicted in those Figures.

Figures 5-19 are elucidated below. The invention is not limited to the embodiments of discharge vessels shown in the Figures 16, 17 and 19.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As mentioned above, the lamp of the invention comprises a ceramic discharge vessel. This particularly means that the walls of the ceramic discharge vessel preferably comprise a translucent crystalline metal oxide, like monocrystalline sapphire and densely sintered polycrystalline alumina (also known as PCA), YAG (yttrium aluminium garnet) and YOX (yttrium aluminium oxide), or translucent metal nitrides like AIN. The vessel wall may consist of one or more (sintered) parts, as known in the art (see also below).

Below, an embodiment of the lamp of the invention is described with reference to Figs. 1-3. However, the lamp of the invention is not confined to the

embodiments described below and/or schematically depicted in Figs. 1-3. Lamp 1 may be a high-intensity discharge lamp. In Figs. 1-3, discharge vessels 3 are schematically depicted. The current lead-through conductors 20, 21 are sealed with two respective seals 10 (sealing frits, as known in the art). However, the invention is not limited to such embodiments. Lamps in which one or both of the current lead-through conductors 20, 21 are, for example, directly sintered into the discharge vessel 3 may also be considered.

Herein, a more detailed description is given of specific embodiments, in which both current lead-through conductors 20, 21 are sealed into discharge vessel 3 by means of seals 10 (see also Figs. 1-3). Two electrodes 4, 5, for example tungsten electrodes, with tips 4b, 5b at a mutual distance EA are arranged in the discharge space 11 so as to define a discharge path between them. The cylindrical discharge vessel 3 has an internal diameter D at least over the distance EA. Each electrode 4, 5 extends inside the discharge vessel 3 over a length forming a tip-to-bottom-distance between the vessel wall 31 (i.e. reference signs 33a, 33b (see also below), respectively) and the electrode tip 4b, 5b. The discharge vessel 3 may be closed on either side by means of end wall portions 32a, 32b forming end faces 33a, 33b of the discharge space. The end wall portions 32a, 32b may each have an opening in which a respective ceramic projecting plug 34, 35 is fitted in a gastight manner by means of a sintered joint S. The discharge vessel 3 is closed by means of these ceramic projecting plugs 34, 35, each of which encloses a current lead-through conductor 20, 21 (in general including respective components 40, 41; 50,51, which are explained in more detail below) extending to electrodes 4, 5 positioned in the discharge vessel 3 with a narrow interspace and connected to this conductor in a gastight manner by means of a melting-ceramic joint 10 (further indicated as seal 10) at an end remote from the discharge space 11. Here, the ceramic discharge vessel wall 30 comprises vessel wall 31, ceramic projecting plugs 34, 35, and end wall portions 32a, 32b.

The discharge vessel 3 is surrounded by an outer bulb 100 which is provided with a lamp cap 2 at one end. A discharge will extend between the electrodes 4 and 5 when the lamp 1 is operating. The electrode 4 is connected via a current conductor 8 to a first electrical contact forming part of the lamp cap 2. The electrode 5 is connected via a current conductor 9 to a second electrical contact forming part of the lamp cap 2.

The ceramic projecting plugs 34, 35 each narrowly enclose a current lead- through conductor 20, 21 of a relevant electrode 4, 5 having electrode rods 4a, 5a which are provided with tips 4b, 5b, respectively. Current lead-through conductors 20, 21 enter discharge vessel 3. In an embodiment, the current lead-through conductors 20, 21 may each comprise a halide-resistant portion 41, 51, for example in the form of a M0-AI₂O₃ cermet, and a portion 40, 50 which is fastened to a respective end plug 34, 35 in a gas tight manner by means of seals 10. Seals 10 extend over the Mo cermets 41, 51 (during sealing, ceramic sealing material penetrates into the free space within the respective end plugs 34, 35) over some distance, for example approximately 1-5 mm. The parts 41, 51 may alternatively be formed from material other than M0-AI₂O₃ cermet. Other possible constructions are known, for example, from EP0587238 (incorporated herein by reference, wherein a Mo coil-to-rod configuration is described). A particularly suitable construction was found to be a halide- resistant material. The parts 40, 50 are made from a metal whose coefficient of expansion corresponds very well to that of the end plugs 34, 35. Niobium (Nb) is chosen, for example, because this material has a coefficient of thermal expansion corresponding to that of the ceramic discharge vessel 3.

Fig. 3 shows another embodiment of the lamp according to the invention. Lamp parts corresponding to those shown in Figs. 1 and 2 have been given the same reference numerals. The discharge vessel 3 has a shaped wall 30 enclosing the discharge space 11. The shaped wall 30 forms an ellipsoid in the case shown here. Compared with the embodiment described above (see also Fig. 2), the wall 30 is a single entity, in fact comprising wall 31, respective end plugs 34, 35, and end wall portions 32a, 32b (shown as separate parts in Fig. 2). A specific embodiment of such a discharge vessel 3 is described in more detail in WO06/046175. Alternatively, other shapes, like for example spheroid, are equally possible.

Herein, wall 30, which in the embodiment schematically depicted in Fig. 2 may include ceramic projecting plugs 34, 35, end wall portions 32a, 32b, and wall 31 or wall 30, as schematically depicted in Fig. 3, is a ceramic wall, which is to be understood to mean a wall of translucent crystalline metal oxide or translucent metal nitrides like A1N (see also above). According to the state of the art, these ceramics are well suited to form translucent discharge vessel walls of vessel 3. Such translucent ceramic discharge vessels 3 are known, see for example EP215524, EP587238, WO05/088675, and WO06/046175. In a specific embodiment, the discharge vessel 3 comprises translucent sintered AI₂O₃, i.e. wall 30 comprises translucent sintered AI₂O₃. In the embodiment schematically depicted in the Figures, wall 30 may also comprise sapphire.

The filling in the lamp 1 of the invention may, in an embodiment, comprise (a) Nal and/or Lil, (b) Til, (c) optionally Cal₂, and (d) Ce and/or Dyl₃, but may also further comprise other salt filling components such as especially Inl, Prl₃, H0I3, Tml₃, Bal₂ and Snl₂, for instance for obtaining a specific color temperature and/or color rendering index. Also one or more other additives may be present, selected from the group of iodides of Cs, Rb, K, Sr, Nd, Yb and La. For instance, the salt filing may further comprise strontium iodide and/or ytterbium iodide.

Furthermore, the discharge space 11 contains Hg (mercury) and a starter gas such as Ar (argon) or Xe (xenon), as known in the art. Mercury and a starter gas are implied, as known to those skilled in the art, and are not further discussed. In principle, the lamp of the invention may also be operated free of mercury, but Hg is present in the discharge vessel 3 in the preferred embodiments.

During steady-state burning (herein also indicated as nominal operation), long- arc lamps in general have a pressure of a few bar, whereas short-arc lamps may have pressures in the discharge vessel of up to about 50 bar. Characteristic powers of the lamp are between about 10 and 1000 W, preferably in the range of about 20-600 W.

Figure 4 schematically depicts a further embodiment of the discharge vessel 3, wherein the current-lead through conductors 20, 21 are sintered in the respective end plugs 34, 35. Further, the discharge vessel 3 comprises a side filling channel 200. After the discharge vessel 3 has been produced, the discharge vessel 3 can be filled with the salt filling and other filling materials like filling gas and/or mercury, via this side filling channel 200. Thereafter, the filling channel 200 is closed, for instance by melting/sintering the filling channel 200. In this way, a side extension remains at the discharge vessel 3.

Below, an overview is given of a number of lamps according to the invention, which have been tested. As the rare gas filling mainly Ar was used with a filling pressure of about 150 and 400 mbar at room temperature. Other possible gas fillings comprise Ne, Kr, Xe or mixtures thereof. All lamps also comprised Hg in the filling. In the overview, the lamp fillings mentioned are in μιηοΐε/αη³ and μgram/mm³. The fillings mentioned in the table are all iodides.

Overview Table 1 : 70W 4200K lamps. Electrode distance 6 mm, inner diameter 6.4 mm

Table 2: 70W 3000K lamps. Electrode distance 6 mm, inner diameter 6.4 mm type wall load (W/cm²) volume (mm³) Nal Til Cal₂ Cel₃

μιηοΐε/αη³

V2,2 33 280 2.39 1.03 0.04 0.12

V5,5 33 280 2.39 1.03 0.04 0.12

V6,6 36 238 2.81 1.21 0.05 0.14

V3,3 29 325 2.06 0.88 0.03 0.10

V7,7 32 273 2.45 1.05 0.04 0.12

V4,4 36 251 2.66 1.14 0.04 0.13 type wall load (W/cm2) volume (mm3) Nal Til Cal₂ Cel₃

μgram/mm³

V2,2 33 280 0.359 0.341 0.012 0.063

V5,5 33 280 0.359 0.341 0.012 0.063

V6,6 36 238 0.421 0.401 0.015 0.073

V3,3 29 325 0.309 0.291 0.009 0.052

V7,7 32 273 0.368 0.348 0.012 0.063

V4,4 36 251 0.399 0.377 0.012 0.068 Further lamps were tested, which are indicated in the tables 3 and 3b herebelow.

Tables 3: 70W 3000K lamps. Electrode distance 6 mm, inner diameter 6.4 mm

The reference lamp has a gas filling which is outside the preferred embodiments of the invention. This lamp also has a relatively low lifetime. The lifetime and light technical properties of the other two lamps, however, are satisfactory to good.

Table 4: 50W lamps. Electrode distance 4.2 mm, inner diameter 4.44 mm

Table 5: 39W lamps. Electrode distance 4 mm, inner diameter 4.44 mm

Also 20 W lamps were manufactured with an electrode distance of 3 mm, inner 3 mm, wall load 39 W/cm², volume 30 mm³. A lamp with Tc = 4200K has a filling comprising 0.76 μιηοΐε/αη³ Li, 3.59 μιηοΐε/αη³ Tl, 0.75 μιηοΐε/αη³ Dy. A lamp with a Tc = 3000K has a filling comprising 3.66 μιηοΐε/αη³ Na, 1.73 μιηοΐε/αη³ Tl, 0.18 μιηοΐε/αη³ Ce.

In Figure 5, light technical properties of a 4000 K metal halide CDM lamp are given for a conventional lamp and a lamp according to the invention. As can be seen in Figure 4, the light technical properties of the lamp according to the invention remain high with only a limited color shift with dimming, while the conventional lamps shift to the green with a strong drop in light technical properties;

Color point results for the lamps with Tc = 4200K are shown in Fig 6;

In Figs. 7 to 10 the results are shown for these lamps as regards luminous efficacy, color temperature Tc, general color rendering index Ra and color rendering for red R9, respectively, when being dimmed;

Color point results for the lamps with Tc = 3000K are shown in Fig 11;

In Figs. 12 to 15 the results for these lamps, when being dimmed, are shown as regards luminous efficacy, color temperature Tc, general color rendering index Ra and color rendering for red R9, respectively;

Fig. 16 shows an X-ray view of a discharge vessel of the 70W lamp type v2,2 with a thin wall;

Fig. 17 shows an X-ray view of a discharge vessel of the 39W lamp;

Fig. 18 shows the effect on the color point, when dimming the 50W 3000 K lamp; and

Fig. 19 shows an X-ray view of a discharge vessel of the 50W lamp.

Further explanation of the Figures

Specific embodiments

Specific embodiments are indicated below. Those specific embodiments are numbered only for the sake of understanding:

1. A discharge lamp comprising a ceramic discharge vessel that encloses a discharge volume with an aspect ratio of at maximum about 4 and a wall load at normal operation at full power of at least about 25W/cm² comprises at least 2 electrodes, a dischargeable gas that consists of a noble gas or a mixture of noble gasses and a mixture of metal halides, wherein the lamp has a power density defined as the inner surface of the discharge vessel divided by the nominal lamp power and an aspect ratio defined as the electrode distance divided by the inner diameter and a wall thickness between about 0.3 mm and about 1.2 mm.

2. As 1, additionally containing partial sodium and/or lithium metal halides in a quantity above about 0.02 μg/mm³ and below about 1.1 μg/mm³.

3. As 1, with a mixture of metal halides that consist of a rare-earth halide filling or a mixture of rare earths and a sodium halide filling with, based on sodium iodide, a content of at minimum O.^g/mm³ and at maximum 0.5 μg/mm³.

4. As 1, with a mixture of metal halides that consist of at least a rare earth halide filling and a lithium halide filling, the content thereof, based on lithium iodide, being at least about 0.1 μg/mm3 and at maximum about 0.8 μg/mm³.

5. As 1,2,3,4,5 and containing also mercury.

6. As 1,2,3,4,5 and comprising a combination of the following measures:

a) Wall load at full power of at least about 25 W/cm² (Wall load is defined as lamp power divided by the inner surface).

b) Filling: Low content of metal halide filling.

a. Warm white (typically 3500 - 2500 K).

i. RE content between 0.008 and 0.1 μg/mm³ or 0.015μιηο1Λ;ιη³ to 0.2 μιηοΐ/cm³, preferably selected from Ce, Pr, La, Dy or mixtures of rare earth (RE)

components.

ii. Sodium content between -0.02 +5*RE and 0.10 +10*RE [^g/mm³] or between -0.13+17*RE and 0.67+37*RE μιηοΐ/cm³.

iii. Tl-halides = between 0.75 * Na halides and Na-halides +0.9 |^g/mm3] or between 0.35* NA and 0.45 * Na + 0.41 μιηοΐ/cm³.

iv. Additional small amounts of other materials like Ca, Mg, Li.

b. Cool white (typically 3500 - 5000 K). i. Re content between 0.05 and 0.5 μ .ηιηι³ or between 0.1 and 1 μηιοΐ/cm³, preferably comprising Dy, Ce, Pr, La, and /or mixtures of rare earth components.

ii. Na and/or Li halides between O. lxRE and lxRE halide content or between 0.35 * RE and 4.1 * RE μιηοΐ/cm³.

iii. Tl in a quantity of at least 40% of the total mass: RE and Na and Li content and Tl halides.

c) An aspect ratio of the burner that is typically below 3.5. "Aspect ratio" is defined as the electrode distance divided by the inner diameter, which is preferably between about 0.5 and about 2.

The term "substantially" herein, such as in "substantially all emission" or in "substantially consists", will be understood by the person skilled in the art. The term

"substantially" may also include embodiments with "entirely", "completely", "all", etc. Hence, in embodiments, the adjective substantially may also be removed. Where applicable, the term "substantially" may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term "comprise" includes also embodiments wherein the term "comprises" means "consists of.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in sequences other than those described or illustrated herein.

The devices used herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A metal halide lamp (1) comprising a ceramic discharge vessel (3), having an inner diameter (D), enclosing a discharge space (11) which accommodates two electrodes (4, 5) arranged at an electrode distance (EA), and which contains a noble gas and a salt filling, wherein:

the salt filling comprises an alkali halide, a rare earth halide, and optionally thallium halide, wherein the discharge space contains 0.015-1.5 μg/mm³ alkali halide;

the discharge vessel has an aspect ratio, defined as the electrode distance (EA) divided by the inner diameter (D), of at maximum 4; and

2. The metal halide lamp (1) according to any one of the preceding claims, wherein the aspect ratio is in the range of 0.5-2.

3. The metal halide lamp (1) according to any one of the preceding claims, wherein the wall load is in the range of 25-50 W/cm².

4. The metal halide lamp (1) according to any one of the preceding claims, wherein the discharge vessel (3) comprises a closed side-filling channel (200).

5. The metal halide lamp (1) according to any one of the preceding claims, wherein the alkali halide comprises one or more of sodium halide and lithium halide.

6. The metal halide lamp (1) according to any one of the preceding claims, wherein the discharge space contains thallium halide.

7. The metal halide lamp (1) according to any one of the preceding claims, wherein the discharge space contains 0.02-1.1 μg/mm³ alkali halide.

8. The metal halide lamp (1) according to any one of the preceding claims, wherein the discharge space contains 0.1-0.5 μg/mm³ sodium iodide.

9. The metal halide lamp (1) according to any one of the preceding claims, wherein the discharge space contains 0.1-0.8 μg/mm³ lithium iodide.

10. The metal halide lamp (1) according to any one of the preceding claims, wherein the halides are iodides, and wherein the salt filling comprises at least one or more iodides selected from the group consisting of cerium, praseodymium and dysprosium iodide.

11. The metal halide lamp (1) according to any one of the preceding claims, wherein:

i. the rare earth halide content is between 0.008 and 0.1 μg/mm³ and wherein the rare earth halide comprises one or more halides selected from the group consisting of Ce, Pr, La, and Dy halides;

ii. the sodium halide content is between -0.02 +5 *RE halide and 0.10 +10*RE halide ^g/mm³];

iii. the Tl halide is between 0.75 * Na halide and Na-halide +0.9 ^g/mm³]; iv. the salt filling further comprises one or more of Ca, Mg, and Li halides.

12. The metal halide lamp according to claim 11, having, at nominal lamp power, a color temperature in the range of 2500 K-3500 K.

13. The metal halide lamp (1) according to any one of the preceding claims, wherein:

i. the rare earth halide content is between 0.05 and 0.5 μg/mm³ and wherein the rare earth halide comprises one or more halides selected from the group consisting of Dy, Ce, Pr, and La halides;

ii. the alkali halide content is between O.lxRE halide and lxRE halide [^g/mm³]; iii. the Tl halide content is at least 40% of the total mass of rare earth halides, alkali halides and Tl-halide.

14. The metal halide lamp according to claim 11, having, at nominal lamp power, a color temperature in the range of 3500-5000 K.

15. The metal halide lamp (1) according to any one of the preceding claims, wherein the electrodes (4,5) are in electrically conductive contact with current lead-through conductors (20,21), wherein the current lead-through conductors (20,21) are directly sintered in the discharge vessel (3).