Electric lamp and discharge devices – With temperature modifier – Double wall – jacket or casing for envelope
Reexamination Certificate
1998-05-07
2001-06-05
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With temperature modifier
Double wall, jacket or casing for envelope
C313S017000, C313S027000, C313S047000, C313S493000, C313S634000, C313S635000
Reexamination Certificate
active
06242851
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to dimmable high pressure arc discharge lamps emitting primary white light for general illumination.
BACKGROUND OF THE INVENTION
Metal halide lamps have been commercially available for about 30 years. Since then, overall lamp performance has been continuously improving. Such improvements include increasing the efficiency and the life of the lamps. Utilization of various materials, including rare earth halides, have yielded substantially higher color rendering index (CRI) at various correlated color temperatures (CCT). More recently, metal halide lamps, with ceramic arc tubes of polycrystalline alumina and compatible special frit materials, have dramatically improved the color consistency of such lamps. The ceramic arc tubes enable metal halide lamps to operate with a much smaller color spread. Also, lamp-to-lamp color variation has been reduced dramatically. Over the last several years, the need to save energy has become more acute due to global warming issues and, as a result, many researchers have been investigating ways of reducing the energy consumption of lighting. Dimming the lamps, of course, generally allows saving energy when full light output is not necessary. In industrial and commercial establishments the dimmed period could be between store closing hours such as 8:00 p.m. or 11:00 p.m. In outdoor applications it could be between 11:00 p.m. and 6:00 a.m. However, when existing metal halide lamps are dimmed, the metal halide vapor pressure in the arc tubes drops dramatically resulting primarily in a mercury discharge in which the CCT of the dimmed metal halide lamp is much higher than the CCT of the lamp when it is operating at rated wattage.
This change of CCT is disturbing and very perceptible to the viewer. R. G. Gibson, “Dimming of Metal Halide Lamps,” Journal of IES, Summer 1994, has investigated the issue in lamps which utilize phosphor-coated outer jackets. The phosphor is typically europium-activated yttrium vanadate which responds to the 365 nm emission line of mercury. As a result, when the lamp is dimmed, the mercury UV radiation is converted into more reddish emission from the phosphor coating which results in a relatively small color change. However, this is only for coated lamps and the effects are limited. Clear lamps do not have the advantage of being able to convert mercury radiation into more reddish visible radiation. Coated lamps are more expensive to manufacture and have more limited applications. Therefore, it is highly desirable to have dimmable clear jacket lamps without substantial CCT change under dimming.
In addition to saving energy in high bay and outdoor applications or industrial and commercial installations by turning down the light source, there are also applications in mood control, especially at the lower power levels (e.g., 150 W or lower). This could be in applications where metal halide lamps are used primarily indoors, such as restaurants, residential and semi-commercial installations or entertainment establishments, where color has to be maintained under continuous dimming.
A further application for dimmable metal halide lamps is where one wants to maintain constant light output throughout the life of the lamps. As is well known, under normal circumstances, where the lamp is operated at rated power over its life, there will be some light output depreciation which can be as much as 40-50% depending on the maintenance, chemistry and power level of the lamp. In some applications this is quite objectionable and the environment is not well served by that kind of light output depreciation. Therefore, compensation could be produced by either overdriving the lamp (which shortens the life considerably) or starting from a 20-30% reduced power state, so as luminosity decreases, lamp power increases automatically to produce a constant light output through the life of the lamp. This can be done with electronic power controls and sensors.
When commercially available metal halide lamps are dimmed, typically the color temperature increases from 500° K to about 1500° K, depending on the lamp chemistry. Furthermore, one of the dramatic changes that takes place (especially for rare earth chemistries) is the hue of the light source changes from white to somewhat greenish. Such lamps contain (in addition to rare earth halides) thallium iodide and sodium iodide to improve the efficacy. The vapor pressures of the rare earth halides are substantially different than thallium iodide at different temperatures. Thallium iodide typically is unsaturated and has a higher vapor pressure than the vapor pressures of the rare earth halides. When the lamps are dimmed 30 or 50% in power, the cold spot temperature drops. The less volatile rare earth halide vapor pressure drops dramatically, whereas the thallium iodide remains in the gas phase and gives a greenish hue to the lamps. When thallium iodide is removed so only rare earth halides remain, the efficiency is not as high as it could be, or has been shown to be possible, under full rating of the lamps.
OBJECTS OF THE INVENTION
Therefore, an object of the present invention is to provide a metal halide light source which is dimmable for energy saving applications.
Another object is to have a metal halide light source which is dimmable down to about 50% power level, while maintaining high efficiency and minimum color temperature change.
A further object is to provide a light source with high CRI under both dimmed and rated power conditions.
Another object is to provide a metal halide light source which has continuous dimming possibilities and minimum color temperature change which would not be perceptible to the eye.
A further object of the invention is to provide a metal halide light source that is dimmable for all the different CCTs (3000, 4100, 4500, 5000° K, etc.) and all power levels (35 W to 400 W and above).
Another object of the invention is to provide a metal halide light source that is dimmable for all the different chemistries.
A further object of the present invention is to provide a dimmable light source that is compatible with high and low frequency electronic ballast operation, as well as magnetic ballast operation.
Still another object is to provide a dimmable metal halide light source with a clear outer jacket that substantially maintains its color temperature (CCT) when dimmed.
SUMMARY OF THE INVENTION
According to the present invention, a metal halide lamp can be dimmed to about 50% power while maintaining the color substantially the same as it is at rated power, while maintaining a high efficacy and CRI during the dimming as well as rated power conditions. The invention is applicable to a whole variety of metal halide lamps at different power levels, as well as different chemistries.
We have discovered one of the most effective ways of maintaining metal halide lamp performance under dim, as well as rated conditions, is to improve the thermal environment within the arc tube. That is, we have discovered if ingredients of the lamp chemistry are prevented from condensing when dimming the lamp, then the overall performance of the lamp can be maintained. In order to do that we had to increase, somewhat, the cold spot temperature under rated conditions in such a manner that under dimmed conditions we have just a very small change in cold spot temperature.
According to the present invention, we provide at least one metal heat shield on the outside of a ceramic arc tube, near the electrode areas, so as little light output as possible is blocked, but yet provide a higher cold spot temperature under dimmed conditions. This is primarily accomplished as a result of the characteristics of the metal and its emissivity relative to the emissivity of ceramic materials. The metals suitable for the heat shield materials have lower emissivity at lower temperatures. For the entire temperature range of the cold spot during a dimming operation, the metals have lower emissivity than aluminum oxide or zirconium oxide, the conventional coating materials on the ends o
Maya Jakob
Zhu Huiling
Haynes Mack
Matsushita Electric Works Research and Development Laboratory In
Patel Nimeshkumar D.
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