Electric lamp and discharge devices – Having vapor generating material – Electrode or electrode support includes material
Reexamination Certificate
1999-05-18
2001-10-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Having vapor generating material
Electrode or electrode support includes material
C313S565000, C313S564000, C313S550000, C313S556000
Reexamination Certificate
active
06304030
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a low-pressure mercury vapor discharge lamp comprising a discharge vessel,
which discharge vessel encloses a discharge space containing a filling of mercury and an inert gas in a gastight manner,
an electrode being arranged at each end portion in the discharge space for generating and maintaining a discharge in the discharge space,
current supply conductors of the electrodes extending through the end portions so as to project from the discharge vessel,
and at least one of the current supply conductors carrying an amalgam.
In mercury-vapor discharge lamps, mercury constitutes the primary component for (efficiently) generating ultraviolet (UV) light. An inner wall of the discharge vessel may be coated with a luminescent layer comprising a luminescent material (for example a fluorescent powder) for converting UV light to other wavelengths, for example UV-B and UV-A for tanning purposes (sunbed lamps) or to visible radiation. Such discharge lamps are therefore also referred to as fluorescent lamps.
A low-pressure mercury vapor discharge lamp of the type mentioned in the opening paragraph is known from U.S. Pat. No. 4,105,910. In the known discharge lamp, the current supply conductor carries an amalgam which is provided on a metal plate which is secured to the current supply conductor. This amalgam acts as an auxiliary amalgam and serves to increase the run-up rate, that is the rate at which the discharge lamp approximates its rated light intensity after having been switched on. This is achieved by the fact that, after switching-on the lamp, heat originating from the electrode causes the amalgam to give off the mercury bonded thereto, thereby causing the mercury vapor pressure in the discharge vessel to increase to a value which is desired for nominal operation. This has the drawback, however, that the plate entails extra costs due to its manufacture, storage, transport and assembly with other parts of the discharge lamp.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a low-pressure mercury vapor discharge lamp which more rapidly reaches its rated light intensity. The invention further aims at providing a low-pressure mercury vapor discharge lamp which can be manufactured more economically.
In accordance with the invention, characterized in that the amalgam covers a region of a segment of the current supply conductor, which segment connects the end portion to the electrode, and which region is situated at a distance d
a
from the end portion, where d
a
>0.
Since the amalgam is provided on the current supply conductor at a location relatively close to the electrode, the heat generated in the electrode after the lamp has been switched on is better, and more rapidly, dissipated to the amalgam, so that the warming-up time of the amalgam is reduced, causing the mercury vapor pressure in the discharge space to increase more rapidly, and hence the value of the mercury vapor pressure desired for nominal operation to be reached sooner.
In the low-pressure mercury vapor discharge lamp disclosed in U.S. Pat. No. 4,105,910, a region of the (glass) end portion of the discharge vessel is coated with amalgam. The coating also extends over a region of a current supply conductor which borders on the end portion. At the end of the service life of the lamp, the amalgam constitutes a point of action for the discharge arc. At this stage, the end portion of the discharge vessel is strongly heated, causing it to melt so that air can flow into the discharge vessel and the operation of the lamp is interrupted.
In the low-pressure mercury vapor discharge lamp known from U.S. Pat. No. 5,841,220, the region coated with amalgam extends from a free end portion of the current supply conductor. For this purpose, the current supply conductor is extended relative to the location on the current supply conductor where the electrode is secured. In the discharge lamp in accordance with the invention, the current supply conductor does not have to be extended to reach the desired temperature of the amalgam, because the amalgam is provided on a segment of the current supply conductor which extends between the end portion and the electrode.
The temperature reached by the amalgam during operation of the lamp can be selected by means of the position of the region relative to the electrode. A preferred embodiment of the low-pressure mercury vapor discharge lamp in accordance with the invention is characterized in that the distance d
a
meets the relation:
0.05×d
ep-e
≦d
a
≦0.9×d
ep-e
,
where d
ep-e
is a distance between the end portion and the electrode, and the distance d
a
being measured from the end portion.
The lower limit of the distance (d
a
≧0.05×d
ep-e
) is determined because it is desirable for the amalgam to be positioned not too close to the end portion since this adversely affects the warming-up of the amalgam after switching on the lamp. In the lamp known from U.S. Pat. No. 4,105,910, a region of the end portion is coated with amalgam, which is unfavorable for a rapid warming-up of the amalgam. The upper limit of the distance (d
a
≦0.90×d
ep-e
) is determined because it is desirable to position the amalgam not too close to the electrode since this has an unfavorable effect on the amalgam if the lamp is in operation for a long period of time. In this manner, it is further precluded that amalgam finds it way to the electrode, which would hamper the electron-emitting effect of the electrode. In addition, if amalgam would find its way to the electrode, it could spread further in the discharge vessel from the electrode, which generally adversely affects the mercury vapor pressure. A suitable temperature of the auxiliary amalgam is obtained, in particular, if 0.1×d
ep-e
≦d
a
≦0.5×d
ep-e
.
In an attractive embodiment, the amalgam-coated regions of the current supply conductors occupy mutually different positions relative to the electrode. Partly as a result thereof, the auxiliary amalgams thus formed give off mercury at different time intervals after switching on the lamp. In this manner, a temporary excess or shortage of mercury after switching on the lamp can be counteracted.
Preferably, the amalgam is provided directly on the segment of the current supply conductor. This results in a reduction of the number of components of the discharge lamp, so that the discharge lamp can be manufactured more economically. In the discharge lamp known from U.S. Pat. No. 4,105,910, the current supply conductor carries an amalgam which is provided on a metal plate which is secured to the current supply conductor.
In a favorable embodiment, the amalgam is provided, in the low-pressure mercury vapor discharge lamp, on the segment of the current supply conductor by means of soldering or welding. The amalgam can be readily provided in this manner by touching the region of the current supply conductor to be coated with a “soldering iron”, thereby moistening said region with metal from the iron. The so-called “solder tin” contains an amalgam or an amalgam-forming agent, that is an amalgam-forming metal such as indium, tin, lead or bismuth, or an amalgam-forming alloy, for example of lead and tin or of bismuth and indium. In the latter case, the amalgam on the current supply conductor may form, for example, by means of mercury vapor from the discharge space of the discharge vessel after the lamp has been provided with its filling. Soldering or welding at the location of the region to be coated can be enhanced by using a flux. If necessary, a region to be coated may be provided first with a layer of another material in order to improve the adhesion of the coating of amalgam or amalgam-forming agent to the current supply conductor. The coating may alternatively be provided, for example, electrolytically. The quantity of amalgam on the relevant region can be readily chosen by those skilled in the art by varying the thickness of the current supply conductor and the length of the region The current supply conducto
Driessens Rene M. A.
Ooms Pieter C.
Patel Nimeshkumar D.
Santiago Mariceli
Spain Norman N.
U.S. Philips Corporation
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