Patent Application
20110298366
Reference is made to commonly owned, co-pending U.S. patent application Ser. No. ______, filed (Attorney Docket 235549/GECZ 2 00957), 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 for a compact high intensity discharge lamp, and more specifically to a compact metal halide lamp made of translucent, transparent, or substantially transparent quartz, hard glass, or ceramic discharge chamber materials. In particular, the disclosure finds application in the automotive lighting field, although it will be appreciated that selected aspects may find application in related discharge lamp environments encountering similar 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 (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 a 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 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 such as automotive headlight reflectors associated with these types of lamps must consider these issues when designing the beam forming 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 rays passing through the dose film are thus generally ignored and because of this the distorted rays represent losses in the optical system since the distorted rays do not take part in forming the main beam of the optical projection system.
In an automotive headlamp application, for example, these scattered and distorted 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 losses, efficiency of the optical systems 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 lighting 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 optical system designed around the lamp as a result of the uneven light intensity distribution from the lamp.
An improved discharge light source positions a molten metal halide salt pool at a desired location in the discharge chamber.
The discharge light source includes an arc tube having a longitudinal axis and discharge chamber formed therein. First and second electrodes have inner terminal ends spaced from one another along the longitudinal axis and each electrode extends at least partially into the opposite ends of the discharge chamber. The discharge chamber is preferably asymmetric about a second axis that is perpendicular to the longitudinal axis.
In another exemplary embodiment, the discharge chamber preferably includes first and second spheroidal portions of different diameters spaced along the longitudinal axis.
The arc tube has different wall thicknesses in yet another arrangement. The different thicknesses of the wall may be at first and second ends of the discharge chamber. Alternatively, along with the uneven wall thickness, the arc tube has principally the same outer diameter all along its length.
Preferably, the chamber is rotationally symmetric about the longitudinal axis in another embodiment.
In a further exemplary embodiment, a portion of a wall that forms the discharge chamber includes a concave inner surface. The concave surface may be located at a first end of the discharge chamber and a generally spheroidal portion formed at a second end of the discharge chamber. Likewise, wall portions of the arc tube may also have different first and second thicknesses at the first and second ends of the discharge chamber in this alternative arrangement.
In still another embodiment, a light transmissive arc tube encloses a discharge chamber. First and second electrodes at least partially extend into the discharge chamber at its opposite ends and are separated along a longitudinal axis by an arc gap. An enlarged dimension first chamber region is located at one end of the discharge chamber and partially surrounds the first electrode, the dimension of the first chamber region being larger than a dimension of a second chamber region around the arc gap.
The enlarged dimension first chamber region is at least partially located axially outward from the inner terminal end of the electrode, that is, towards the seal portion of the arc tube.
A primary benefit of the present disclosure is a controlled location of a metal halide salt pool in a compact high intensity discharge chamber.
Another benefit is that the dose pool is offset towards at least one of the end portions of the discharge chamber and has less impact on the light distribution, thereby resulting in the lamp being more efficient and providing a more even light intensity distribution. In turn, optical designers can develop a more efficient optical projection system.
Still another benefit of providing a preselected liquid dose pool location in the light source is the ability to address the problem of absorbed, scattered and discolored light rays.
Still other features and benefits of the present disclosure will become more apparent from reading and understanding the following detailed description.
A first embodiment is shown in
As described in the Background, a liquid phase portion of the dosing material is usually situated in a bottom center portion of a horizontally operated discharge chamber. This dose pool adversely impacts lamp performance, light color, and has a strong shading effect that impacts light intensity and spatial light intensity distribution emitted from the lamp. In
In
In contrast,
The embodiments of
In each of the embodiments of
In
The emitted spatial light intensity distribution of the lamps with arc tubes according to the described embodiments becomes more rotationally symmetric, and all of the emitted light can be used by the optical system to form a more intense main beam, for example in better illuminating the road in case of an automotive application. In this way, lamp power consumption can be reduced while still delivering high illumination levels. By way of example, more efficient headlamps applying high intensity discharge lamps of lower energy consumption (e.g., 25 W) can be designed while still keeping road illumination above halogen incandescent levels. It is believed that overall system costs can be reduced approximately 35-40% since no washing and leveling equipment is required by the existing regulations and standards below 2000 lumens lamp luminous flux.
Further, more even lamp performance can be achieved in case of universal burning general lighting applications since the liquid dose pool always resides at the vicinity of at least one of the ends of the discharge chamber irrespective of lamp orientation. In this manner, high intensity discharge lamps with an arc tube according to one of the described embodiments may find wider penetration in indoor applications, and indoor lighting can be of higher quality and efficiency.
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, it will be appreciated that in some instances one or more of the different features described above may be used individually or in combination. It is intended that the disclosure be construed as including all such modifications and alterations.
