Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-06-09
2002-05-14
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S2090SC, C315S246000, C315SDIG007, C313S623000
Reexamination Certificate
active
06388394
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a high-intensity discharge lamp lighting device and a lighting system, which is able to start lighting the high-intensity discharge lamp with compact lighting circuit means.
BACKGROUND OF THE INVENTION
Recently, a compact metal halide lamp with a lighting power in a range of 10-30 W has been developed as a light source for optical fibers or a light source for halogen light bulb substitution. In such a metal halide lamp, the lighting efficiency is three or four times that the halogen light bulb, and remarkably smaller than the fluorescent lamp so as to be used as the light source.
Accordingly, the metal halide lamp as mentioned above is a light source having the advantages of the halogen light bulb and the electric bulb fluorescent lamp. However, since it is a high-intensity discharge lamp, it needs a stabilizer, i.e., lighting circuit means incorporating therein an igniter for generating a relatively high pulse voltage at the starting operation or lighting circuit means not incorporating therein an igniter, and an igniter separated from the lighting circuit means. As a matter of course, though the fluorescent lamp also needs lighting circuit means since it is also the discharge lamp, lighting circuit means of the high-intensity discharge lamp is overwhelmingly large in comparison with that of the electric bulb fluorescent lamp. Thus, even though a compact high-intensity discharge lamp would be developed for all troubles, an overall system containing a light source, a stabilizer, i.e., lighting circuit means and a lighting apparatus unwillingly has a large size.
To solve the above problem, the inventor has contemplated using a lighting circuit means principally comprising a compact high-frequency inverter, which is used for the fluorescent lamp especially for the electric bulb fluorescent lamp. This lighting circuit means for the electric bulb shaped fluorescent lamp is generally simple in its circuit arrangement, and works at a high-frequency. Accordingly, such a stabilizer is compact, light in weight and less-expensive.
However, when a high-intensity discharge lamp is lighted using such compact lighting circuit means for the fluorescent lamp, an intense blackening occurs at a starting operation.
As a result, the inventor has made investigations in detail about the cause and the measure of the blackening, and the following conclusions have been obtained. (1) Materials of the blackening are principally constituted by tungsten constituting electrodes.
(2) The blackening is caused by the fact that the tungsten of the electrodes evaporates at the starting operation, especially at the glow-arc transition. Then the tungsten sticks on the inner surface of the light-transmissive ceramic discharge enclosure.
Further to the conclusion, it is clarified that as a result of another investigation about the behavior of the electrode at the glow-arc transition in comparison with the lighting circuit of the conventional high-intensity discharge lamp which does not cause such a blackening at the starting operation, the blackening is caused by the difference of load characteristics between the fluorescent lamp lighting circuit and the high-intensity discharge lamp lighting device.
FIG. 1
is a graph showing load characteristics of a high-intensity discharge lamp lighting circuit means and a fluorescent lamp lighting circuit means.
In
FIG. 1
, the horizontal axis represents a current and the vertical axis represents a voltage.
In
FIG. 1
, also the curve A shows the load characteristics of the high-intensity discharge lamp stabilizer, and the curve B shows the load characteristics of the fluorescent lamp stabilizer. Here, as the rated operation points of the high-intensity discharge lamp of both stabilizers occur in a voltage range of 72-75 V and the current is in a range of 280-340 mA of the load characteristics, the rated operation points of the two types of the stabilizers are almost same.
However, the load characteristics of the high-intensity discharge lamp stabilizer, as shown in the characteristic curve A, the secondary open-circuit voltage V
20
is relatively low, but the secondary short-circuit current Is is relatively high. This is because a higher pulse voltage is generated by an igniter at a starting operation, and then superposed to the output voltage of the stabilizer and lastly the superposed voltage is supplied to the lamp, so that, the stabilizer is not required to generate a much high voltage at the starting time. Further since the lamp voltage is low at the starting time in the high-intensity discharge lamp the lamp current is enlarged.
On the other hand, as shown in the curve B, in the load characteristics of the fluorescent lamp stabilizer, the secondary open-circuit voltage V
20
is relatively high but the secondary short-circuit current is relatively slow. Then, the curve B smoothly extends across these two points. Accordingly, in the lower current region corresponding to the glow-arc transition time, e.g., in the region lower than the 30 mA, a secondary supply voltage is higher than the load characteristics of the high-intensity discharge lamp stabilizer.
Further, as the result of determining a glow power at the glow-arc transition, the glow power in the case of using the fluorescent lamp stabilizer was several times higher than that in the case of using the high-intensity discharge lamp stabilizer.
From the above facts, it is thought that the blackening is caused by the evaporation of the tungsten constituting electrodes under an excessive glow power.
On the other hand, it has been found that the blackening is influenced by a glow-arc transition time. That is, in a case of lighting a high-intensity discharge lamp provided with a silica glass discharge enclosure by a stabilizer, i.e., a lighting circuit means for conventional and typical coil and iron-core type high-intensity discharge lamp, a blackening occurring at a starting time is caused by spattering of tungsten electrodes due to mercury ions and rare gas ions during glow-discharge. Thus conventionally it was considered that the glow-arc transition time should be as short as possible for suppressing the blackening.
However, according to studies of the inventor, in the high-intensity discharge lamp provided with the light-transmissive ceramic discharge enclosure, it was found that in much shorter glow-arc transition time the blackening is accelerated due to a specific construction and a unique behavior of the discharge enclosure. On the contrary it was found that in much longer glow-arc transition time the blackening is also accelerated.
Here, a relation between the glow-arc transition time and the blackening will be explained.
That is, a high-intensity discharge lamp provided with a light-transmissive ceramic enclosure is comprised of an envelope defining a discharge space and small diameter cylinder portions communicating with the envelope. An electrode supporting portion is inserted inside the small diameter cylinder portion thus defining a narrow gap called a capillary between the inner wall of the small-diameter cylinder portion and the electrode supporting portion. When the high-intensity discharge lamp operates at a stable lighting condition, a surplus discharge agent resides at a liquid-phase in a bottom of the narrow gap and its surface presents a coldest portion in the lamp. Thus during a delighting of the high-intensity discharge lamp a large amount of the discharge agent deposits in the narrow gap and contacts to the electrode at the liquid-phase or a solid phase.
When the high-intensity discharge lamp is started, the whole electrode supporting portion in the narrow gap and the main portion of the electrode operate as an electrode and thus a glow discharge occurs around them. At this time, a part of a glow-arc transition power is consumed for evaporating the discharge agent. Thus almost the entire discharge agent temporarily evaporates. This delays a temperature rise to a glow-arc transition temperature required for the glow-arc transition and thus
Ashida Seiji
Honda Hisashi
Mita Kazutoshi
Philogene Haissa
Pillsbury & Winthrop
Toshiba Lighting & Technology Corporation
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