Reference is made to commonly owned, co-pending U.S. patent application Ser. No. 12/793,398, filed Jun. 3, 2010, Ser. No. 12/793,441, filed Jun. 3, 2010, and Ser. No. 12/793,494, filed Jun. 3, 2010.
The present disclosure relates to a compact high intensity discharge lamp and especially to an arc tube for a compact high intensity discharge lamp, and more specifically to an arc tube of a compact metal halide lamp made of translucent, transparent or substantially transparent quartz glass, hard glass, or ceramic arc tube materials. It finds particular application, for example in the automotive lighting field, although it will be appreciated that selected aspects may find application in related discharge lamp environments for general lighting encountering the same issues with regard to salt pool location and maximizing luminous flux emitted from the lamp assembly. For purposes of the present disclosure, a “discharge chamber” refers to that part of a discharge lamp where the arc discharge is running, while the term “arc tube” represents that minimal structural assembly of the discharge lamp that is required to generate light by exciting an electric arc discharge in the discharge chamber. An arc tube also contains the pinch seals with the molybdenum foils and outer leads or lead wires (in the case of quartz arc tubes) or the ceramic protruded end plugs or ceramic legs with the seal glass seal portions and outer leads (in case of ceramic arc tubes) which ensure vacuum tightness of the “discharge chamber” plus the possibility to electrically connect the electrodes in the discharge chamber to the outside driving electrical components via the outer leads pointing out of the seal portions of the arc tube assembly.
High intensity discharge lamps produce light by ionizing a fill, such as a mixture of metal halides, mercury or its replacing buffer alternatives, and an inert gas such as neon, argon, krypton or xenon or a mixture of thereof with an arc passing between two electrodes that extend in most cases at the opposite ends into a discharge chamber and energize the fill in the discharge chamber. The electrodes and the fill are sealed within the translucent, transparent or substantially transparent discharge chamber which maintains a desired pressure of the energized fill and allows the emitted light to pass through. The fill (also known as a “dose”) emits visible electromagnetic radiation (that is, light) with a desired spectral power density distribution (spectrum) in response to being vaporized and excited by the arc. For example, rare earth metal halides provide spectral power density distributions that offer a broad choice of high quality spectral properties, including a wide range of color temperatures, excellent color rendering, and high luminous efficacy.
In current high intensity metal halide discharge lamps, a molten metal halide salt pool of overdosed quantity typically resides in a central bottom location or portion of a generally ellipsoidal or tubular discharge chamber, when the discharge chamber is disposed in a horizontal orientation during operation. Since location of the molten salt pool is always at the coldest part of the discharge chamber, this location or spot is often referred to as a “cold spot” location of the discharge chamber. The overdosed molten metal halide salt pool that is in thermal equilibrium with its saturated vapor developed above the liquid dose pool within the discharge chamber, and is located inside the discharge chamber of the lamp at the cold spot area, usually forms a thin liquid film layer on a significant portion of an inner surface of the discharge chamber wall. In this position, the dose pool distorts a spatial intensity distribution of the lamp by increasing light absorption and light scattering in directions where the dose pool is located within the discharge chamber. Moreover, the dose pool alters the color hue of light that passes through the thin liquid film of the dose pool.
Optical designers must address these issues when designing optics around high intensity arc discharge lamps that employ the described arc tube and discharge chamber arrangement. That is, configuration of the optical system must address absorbed, scattered and discolored light rays and the distorted spatial light intensity distribution caused by the distortion effect of the liquid halide dose pool in the discharge chamber. For example, in the past and even in contemporary automotive headlamp constructions, distorted light rays were/are either blocked out, by non light-transparent metal shields, or these light rays were/are distributed in directions that are not critical for the application. In other words, distorted light rays passing through the liquid dose film at the cold spot area of the discharge chamber are generally ignored. As such, this portion of emitted light from the arc discharge represent losses in the optical system since these distorted rays did/do not take part in forming the main beam of the beam forming optical system.
In an automotive headlamp application, for example, the distorted rays are used for slightly illuminating the road immediately preceding the automotive vehicle, or the distorted light rays are directed to road signs well above the road. Due to these losses, efficiency of the headlamp optical systems is typically no higher than approximately 40% to 50%. Optical losses due to beam distortions caused by dose pool in the discharge chamber in lighting systems for other applications may depend on the required beam characteristics, illumination and beam homogeneity levels, and other parameters.
As compact discharge lamps become smaller in wattage and additionally adopt reduced geometrical dimensions, a solution is required with the light source in order to avoid such losses in the optical assembly or system. An improved optical system equipped with discharge lamps of improved beam characteristics would desirably achieve higher illumination levels along with lower energy consumption of the overall lighting system.
Thus, a need exists to address the issues associated with the liquid dose pool located at the cold spot area within the discharge chamber of compact high intensity discharge lamps, and impact of this on performance and efficiency of optical systems designed around these lamps as a result of the uneven and distorted spatial and colorimetric light intensity distribution emitted by these lamps.
In an exemplary embodiment, an arc tube of a high intensity discharge lamp has first and second electrodes having inner terminal ends spaced from one another to form an arc gap along a longitudinal axis within a main central discharge chamber. Each electrode extends at least partially into the main central discharge chamber or at least reaches reduced diameter end portions of the main central discharge chamber with its inner terminal end. A main central discharge chamber has a configuration that is basically rotationally symmetric about the longitudinal axis. First and second sub-chambers are formed and are located at opposite ends of the main central discharge chamber.
The lamp includes a light transmissive arc tube enclosing the main central discharge chamber and the sub-chambers at opposite ends of the main central discharge chamber. In one embodiment, the first and second sub-chambers are preferably generally spheroidal volume portions located at first and second ends of the main central discharge chamber. The main central discharge chamber is substantially symmetrical about the longitudinal axis and substantially mirror-symmetric relative to a central plane located substantially halfway between the inner terminal ends of the electrodes and which is perpendicular to the longitudinal axis. The first and second sub-chambers are located entirely axially outward of inner terminal ends of the electrodes.
In an exemplary embodiment, the main central discharge chamber has a maximum cross-sectional dimension wider than the first and second sub-chambers at its end.
In another exemplary embodiment, the main central discharge chamber has substantially the same maximum cross-sectional dimension as the first and second sub-chambers at its end.
In another exemplary embodiment, the main central discharge chamber has a substantially smaller maximum cross-sectional dimension than the first and second sub-chambers at its ends. The volumes of the main central discharge chamber and that of the first and second sub-chambers are not separated by a reduced diameter end portions of the main central discharge chamber. The sub-chambers of increased cross-sectional dimension are formed axially outward of the inner terminal ends of the electrodes.
In another exemplary embodiment, only one of the sub-chambers is present at one end of the main central discharge chamber of the lamp. The arc tube assembly of the lamp in this embodiment is asymmetrical relative to a central plane that is located basically halfway between the two inner terminal ends of the electrodes in the main central discharge chamber and perpendicular to the longitudinal axis of the arc tube.
The molten metal halide salt pool or “dose” pool resides in the sub-chambers at a desired cold spot location away from the arc discharge developed between the inner terminal ends of the electrodes within the main central discharge chamber which minimizes potential adverse impact of the dose pool on light luminous flux, spatial intensity distribution, and color emitted from the lamp.
A method of controlling the location of a cold spot in a discharge light source includes providing an arc tube having a longitudinal axis and a main central discharge chamber formed therein. The method further includes orienting first and second electrodes having inner terminal ends spaced from one another to form an arc gap along the longitudinal axis and extending each electrode at least partially into the main central discharge chamber or at least reaching endpoints of the main central discharge chamber with each of the inner terminal ends of the electrodes. A main central discharge chamber is disposed between additional sub-chambers located at each end of the main central discharge chamber and which sub-chambers form the cold spot of the arc tube outside the main central discharge chamber.
In the exemplary embodiments, the method further includes locating the first and second sub-chambers entirely axially outward of inner terminal ends of the electrodes, and preferably in most cases even axially completely outward of the reduced diameter end portions of the main central discharge chamber, and the additional sub-chambers are rotationally symmetric about the longitudinal axis.
A primary benefit of the present disclosure is a controlled location of a liquid metal halide salt pool or dose pool in a compact high intensity discharge lamp.
Another benefit is that the liquid dose pool has less impact on emitted light distribution and its other characteristics, thereby resulting in a more efficient lamp with a more even spatial light intensity distribution. In turn, optical designers can develop a more efficient optical system around a compact high intensity discharge lamp of the newly proposed arc tube architecture.
Still another benefit of providing a preselected liquid dose pool location in the light source is the ability to address the optical quality related problems of absorbed, scattered and/or discolored light rays.
Still other features and benefits of the present disclosure will become more apparent from reading and understanding the following detailed description.
With reference to
As described in the Background, in an operational state of the lamp, a liquid phase portion of the dosing material is usually situated in a central bottom portion of a horizontally disposed discharge chamber. This metal halide salt pool or dose pool adversely impacts lamp performance, light color, and has a strong shading effect that impacts spatial light intensity distribution emitted from the lamp. A central portion 146 of the main central discharge chamber extends along a major portion of the chamber in a longitudinal direction. In
In the region surrounding the inner terminal end portion of the electrodes, the main central discharge chamber decreases in cross-sectional dimension. In the particular embodiment of
A thickness of the sidewall varies along the length of the central portion of the arc tube. Particularly, outer surface 170 of the central portion of the arc tube has a generally ellipsoidal conformation about the main central discharge chamber. Since the central portion 146 of the main central discharge chamber has a substantially constant cross-section, the wall thickness changes from a thicker region along a middle portion and reduces in thickness as the inner surface of the arc chamber progresses along the tapering conical portions 150, 152 toward the sub-chambers 160, 162. Where the ellipsoidal outer surface 170 merges with the legs of the arc tube that form the sealed end portions 102, 104, indents or recesses 172, 174 extend about the periphery of the arc tube at these interfaces. This results in a minimal wall thickness in these regions since the recesses are located between the maximum cross-sectional dimensions 164, 166 of the sub-chambers and the minimum cross-sectional dimensions 154, 156 separating the main central discharge chamber and the sub-chambers. The minimized wall thickness portions act as head conduction barriers in the arc tube wall, which makes the temperature of the sub-chambers even lower and helps in formulating the cold spot locations to be formed in the sub-chambers.
The sub-chambers 160, 162 can be formed by simply moving the pinch sealing zones 116, 118 (shown as cross-hatched areas) within the seal/pinch seal portions 102, 104 of the arc tube away from the main central discharge chamber 106. By moving the sealing zones 116, 118 away from the center, hollow portions of well-defined inner volumes are formed within the tubular arc tube legs outward of the reduced diameter end portions 154, 156 of the main central discharge chamber 106, and more specifically outward of the inner terminal ends of the electrodes 124, 126 within the main central discharge chamber. These hollow portions then constitute the first and second sub-chambers after the sealing operation is performed.
The embodiment of
The embodiment of
In sub-chambers 460, 462, the diameter of the set of multiple discharge chambers consisting of the main central discharge chamber and the two sub-chambers is maximized, the temperature of the inner wall is minimized, and thus the sub-chambers form cold spot locations for the liquid dose pool that is in this way to be contained in any or each of the sub-chambers. The dose passageway portions with minimum dimensions 454, 456 of the previous embodiments are completely omitted, that is their diameter is substantially the same as the diameter 448 of the center portion of the main central discharge chamber.
The sub-chambers 460, 462 containing the liquid dose pool and adjoining the end of the main central discharge chamber are advantageous because there is basically light generated outwardly from the inner terminal ends of the electrodes (the arc gap) and therefore there is no adverse impact on light quality emitted by the lamp. On the other hand, at the central portion 446 of the main central discharge chamber 406 where the arc discharge is running between the inner terminal ends 424, 426 of the electrodes, the inner wall of the chamber is clear and has no liquid dose on its inner surface. Consequently, no light absorption, scattering, or discoloration occurs in the central arc chamber portion 446, either. In addition, the sub-chambers, being outside the arc gap region, have no or only very small effect on arc discharge operation.
The embodiment of
As a consequence, no exact correspondence exists between the arc tube components of the two embodiments which is particularly reflected in the alternations of the structure of electrodes and connected outer leads, and the structure of the sealing portions of the arc tubes of the two embodiments. As an example, molybdenum sealing foils 312, 314 in the embodiment of
In
In summary, one or both ends of the main central discharge chamber of the arc tube include sub-chamber(s) formed around the base regions of the electrodes (i.e., at the region where the electrodes contact and are sealed in the arc tube seal end portions). In the preferred embodiments, and especially in the case of applying a glass based arc tube production technology, the small sub-chambers are formed by moving the sealing zone of the pinch seal section away from the end parts of the main central discharge chamber along the axis of the exhaust tubes or arc tube legs adjoining at one or both ends of the central portion of the arc tube. In this way, a well-defined portion of the exhaust tube(s) adjoining the main central discharge chamber stays hollow, forming sub-chamber(s) at the end(s) of the main central discharge chamber. Alternatively, especially in the case of applying a ceramic based arc tube production technology, the small sub-chamber(s) can be formed as an integral part of the arc tube forming process, itself. The small sub-chamber(s) is (are) colder than any part of the main central discharge chamber since only the conducted heat across the electrode(s) and the wall heats these regions and not direct radiation from the arc discharge. Consequently, a major or full quantity of the liquid metal halide dose pool is located within this (these) small sub-chamber(s) since this (these) sub-chamber(s) constitutes the cold spot area(s) of the arc tube. As a result, no liquid dose is found in the main central discharge chamber or at least at its central portion between the inner terminal ends of the opposing electrodes, the light rays are not blocked, and no scattering or discoloration occurs as in prior art arrangements where the dose pool is located in the central portion of the discharge chamber. The spatial light intensity distribution of the light emitted by the lamp becomes more spatially symmetric and all of the light emitted by the arc discharge can be used by the optical system to form a more intense main beam. In this way, lamp power consumption can be reduced while still delivering high illumination levels.
For example, for automotive headlighting applications, smaller headlamps with lower energy consumption (e.g, using a 25 W high intensity discharge lamp instead of the conventional 35 W type) can be designed while still keeping road illumination above halogen incandescent levels. Smaller energy consumption of a lamp or the complete lighting system does not only leads to reduced CO2 emission levels, but also offers the opportunity of a full lamp-electronics system integration, due to the reduced heat dissipation of the system. Potentially overall system cost can be reduced by 30-45% since no washing and leveling equipment is required below 2000 lumens lamp luminous flux. As another application example, more even lamp performance can be achieved in the case of universal burning orientation of a high intensity discharge lamp for general lighting since the liquid dose pool always sits at the end or completely outside of the main central arc chamber of the lamp (that is, in the sub-chambers) irrespective of the lamp orientation.
The disclosure has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that this disclosure be construed as including all such modifications and alterations.
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