Patent Application
20110298367
Reference is made to commonly owned, co-pending U.S. patent application Ser. No. ______, filed ______ (Attorney Docket 235547/GECZ 2 00956), Ser. No. ______, filed ______ (Attorney Docket 235552/GECZ 2 00980) and Ser. No. ______, filed (Attorney Docket 236625/GECZ 2 00981).
This disclosure relates to an arc tube, and more specifically to a discharge chamber formed therein for a compact high intensity arc discharge lamp, and especially to a compact metal halide lamp made of translucent, transparent, or substantially transparent quartz, hard glass, or ceramic arc tube materials. In particular, the disclosure finds application in the automotive lighting field. 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 (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.
High intensity metal halide discharge lamps produce light by ionizing a fill contained in a discharge chamber of an arc tube where the fill is typically a mixture of metal halides and buffer agent such as mercury in an inert gas such as neon, argon, krypton or xenon or a mixture of thereof. An arc is initiated in the discharge chamber between inner terminal ends of electrodes that extend in most cases at the opposite ends into the discharge chamber and energize the fill. In current compact high intensity metal halide discharge lamps, the molten metal halide salt pool of overdosed quantity often resides in a central bottom location of the generally ellipsoidal or tubular discharge chamber, which discharge chamber is disposed in a horizontal orientation during operation. This is the coldest part of the discharge chamber during lamp operation and consequently is often referred to as a “cold spot” location. The overdosed molten metal halide salt pool that is in thermal equilibrium with its saturated vapor developed above the dose pool within the discharge chamber and is situated at the cold spot forms a thin film layer on a significant portion of an inner wall surface of the discharge chamber. This molten metal halide salt pool blocks or filters out significant amounts of emitted light from the arc discharge. The dose pool thereby distorts the spatial intensity distribution of the lamp by increasing light absorption and light scattering in directions where the dose pool sits in the discharge chamber. Moreover, the dose pool alters the color hue of light that passes through the thin liquid film of the dose pool.
Designers of luminaires and optical projection systems, and particularly of automotive headlamps associated with these types of lamps must consider these issues when designing the beam fowling optics. For example, distorted light rays are either blocked by non-transparent metal or plastic shields, or the light rays may be distributed in directions that are not critical for the application. These distorted light rays passing through the dose film are thus generally ignored and because of this the distorted light rays represent losses in the optical system since the distorted light rays do not take part in forming the main beam of the headlamps.
In an automotive headlamp application these scattered and distorted light rays are used for slightly illuminating the road immediately preceding the automotive vehicle, or the distorted rays are directed to road signs well above the road. Because of these beam collection losses, efficiency of the optical systems of automotive headlamps equipped with compact high intensity discharge lamps is typically no higher than about 40% to 50%.
As compact discharge lamps become smaller in wattage, and also adopt reduced geometrical dimensions, a solution is required with the light source in order to avoid such light collection losses in the optical system. This would result in achieving higher illumination levels along with lower energy consumption of the headlighting system.
Thus, a need exists to address the strong shading effect associated with the dose pool, and the impact on performance and efficiency of the headlamp optics designed around the lamp as a result of the uneven light intensity distribution from the lamp.
A discharge lamp includes an arc tube having an arc-shaped discharge chamber formed along a similarly arc-shaped portion of the arc tube. First and second electrodes have inner terminal ends extending at least partially into the discharge chamber from opposite ends. In horizontal orientation during operation, since the discharge arc is bowing in an upward direction due to buoyancy forces acting upon the discharge plasma with temperature gradient across its volume, the arc tube with the arc-shaped discharge chamber is oriented in such way that its shape follows the upward bowing shape of the discharge arc, and thus the first and second ends of the discharge chamber are located at a different height than a central portion of the discharge chamber while the fill material will collect at a cold spot, that is at the coldest portion(s) of the inner wall surface thereof.
A wall thickness is substantially uniform along a length of the arc tube in one embodiment, and may have a non-constant wall thickness in another embodiment.
Inner terminal end portions of the first and second electrodes preferably extend in a direction substantially conforming to the curvilinear shape of the discharge chamber ends.
A central portion of the discharge chamber is equal or slightly wider in cross-section than cross section at the first and second end portions of the discharge chamber, but preferably no greater than 150%, more preferably no greater than 130%, in diameter.
In one exemplary embodiment, a bottom wall apex point of the central portion of the discharge chamber is located above the first and second ends of the discharge chamber in horizontal orientation during operation.
The local cross-section of the discharge chamber is basically rotationally symmetric, preferably of substantially circular cross-section, over a length thereof, and is not coaxial with the first and second ends of the arc tube.
Portions of the first and second electrodes that extend into the discharge chamber extend in substantially parallel relation to the curvilinear conformation of the discharge chamber.
A method of forming a discharge lamp, more preferably a high intensity metal halide discharge lamp, includes providing an arc tube having a curvilinear discharge chamber with a substantially constant wall thickness in some of the embodiments and with varying wall thickness in other embodiments, that is axially disposed between coaxial first and second seal ends and contains an ionizable fill. First and second electrodes are located in the first and second seal ends, respectively, with at least portions extending into the discharge chamber.
A primary benefit of the present disclosure is a controlled location of a metal halide salt pool in a compact high intensity discharge chamber.
A tangential benefit is that the dose pool is offset from the center portion of the discharge chamber and has less impact on the light intensity and on the spatial light intensity distribution emitted by the lamp, thereby resulting in the lamp being more efficient and provides a more even light intensity distribution.
A related benefit is that the automotive headlamp optical designers can develop a more efficient headlamp system.
Still another benefit of providing a precise location for the liquid dose pool in the light source is the ability to effectively address scattered and discolored light rays that typically result from light transmitted through the dose pool located at the cold spot of the discharge chamber.
Still other features and benefits of the present disclosure will become more apparent from reading and understanding the following detailed description.
Turning first to
In the embodiment of
An ionizable fill material is sealed in the discharge chamber and reaches a discharge state in response to an arc initiated or formed between the inner terminal ends of the electrodes in response to a voltage applied to the first and second outer leads. The fill of high intensity metal halide discharge lamps normally includes noble gas component, such as neon, argon, krypton, xenon or a mixture thereof at a well-defined pressure for starting the lamp, metal halides for generating the required luminous flux and spectral power distribution (color) of visible light, and may or may not include mercury as a buffer agent as there is a desire to reduce the amount of mercury in the fill, or to remove mercury entirely therefrom. Typically, an excess amount of metal halide dosing material is provided in the discharge chamber. During operation of the lamp therefore, a liquid phase of the dose of metal halide salts is situated at a cold spot of the discharge chamber as described in the Background.
As evident in
Moreover, the discharge chamber has a generally substantially constant cross-sectional conformation along the length from the first end 142 to the second end 144. In this particular arrangement, the discharge chamber has a rotationally symmetric local cross-section which is substantially a circular cross-sectional conformation along its length in the exemplary embodiment. Further, the outer circumference of the arc tube is also generally constant from the first end to the second end such that wall 146 has a substantially constant thickness over the longitudinal extent of the discharge chamber. However, and as represented by dashed lines 148 in
Orienting the inner terminal ends 130, 132 of the electrodes to turn upwardly from the remainder outer portion of the electrodes, and generally follow the conformation of the arcuate discharge chamber, facilitates formation of defined cold spots along those portions of the discharge chamber adjacent the interface of the electrodes with the seal ends and along end regions 142, 144. As such, the cold spots are located away from a central portion of the discharge chamber and the liquid dose pool situated at the location of the cold spot does not interfere with emitted light from the discharge. In another exemplary embodiment, similar cold spot conditions may be achieved with straight electrodes of preferably short insertion length into the discharge chamber that are coaxially oriented with the longitudinal axis PA. In such preferred cases when a cold spot is positioned at the end regions 142, 144 of the arc chamber, absorption and scattering of the light rays emitted by the arc discharge is considerably reduced, which eliminates issues with discoloring of the light rays passing though the liquid dose film conventionally located at the cold spot in the center bottom portion of the arc chamber, and also aids the optical designers in more consistently handling and directing the light rays in a desired manner. Less light is wasted from the arc discharge leading to less energy required for a given total usefully emitted luminous flux from a lamp.
It will also be recognized in
The degree of curvature or arc in the arc tube may also be limited. For example, and as evident in
Each arrangement achieves a better light performance and higher luminous efficacy by directing the liquid dose to a location in the discharge chamber of the lamp that will not impact the light output from the lamp. All of this is achieved without increasing lamp power or the maximum thermal load imposed on the lamp. Further, it is not necessary to enlarge the outer dimensions of the protective outer envelope of the lamp. By locating the dose pool at the opposite ends, light intensity through the central region of the arc tube is no longer impacted by the shading effect of the dose pool, nor is the color of the light emitted from the arc discharge lamp adversely impacted. Further, the optics for directing the light, such as headlamp optics associated with an automotive discharge lamp application, are more easily handled since a spatially more uniform light intensity distribution is provided from the discharge region. The arc or curvilinear-shaped arc tube preferably has a substantially constant wall thickness throughout the length of the discharge chamber, i.e., the outer dimension of the discharge chamber follows the inner shape and those regions around the base of the electrodes where they enter into the discharge chamber. These end regions act as collector reservoirs or collectors for the liquid dose which are not in the vapor phase during operation. The preferably bent electrodes direct the arc away from these reservoirs and ensure that the position of the cold spot is where desired. As a result of this unique geometry of the arc tube, it is possible to increase and relocate the temperature of the cold spot in the discharge chamber. This again has the advantage that the same light intensity is preferably emitted in a rotationally symmetric manner since the dose pool is relocated to a position outside of the discharge area. The position of the dose pool has less effect on the light distribution thereby making the lamp more efficient, and more even spatial light intensity distribution results, resulting in unhampered light emission from the central region of the discharge chamber. More light is generated which means higher attainable luminous efficacy from the lamp and pet its optical designers to develop a more efficient optical system, or specifically in case of automotive applications a headlamp system of higher light collection efficiency.
When used in an automotive headlamp environment, the arcuate or curvilinear arc discharge will typically operate between about 25 watts and 60 watts, and is operated in a horizontal orientation. In a fully integrated lamp, the driving electronics is attached to the arc tube to form a single complex lamp assembly. Thus, in certain instances, the rated lamp power may or may not take into consideration the power consumption associated with the built-in driving electronics, or may refer to a stand-alone lamp. There is also an increased desire to use an ionizable fill in the discharge chamber that has a reduced amount of mercury, or is even mercury free, when mercury is fully replaced by other less hazardous substance acting as buffer agent in the fill. Thus, the use of the arcuate arc tube is fully applicable to such arrangements, including uses other than automotive applications.
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. For example, the first seal end and the second seal end may not be substantially parallel or co-axially aligned along a longitudinal axis in alternative embodiments. It is intended that the disclosure be construed as including all such modifications and alterations.
