Electric lamp and discharge devices – With luminescent solid or liquid material – With gaseous discharge medium
Reexamination Certificate
2000-01-28
2002-06-11
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
With gaseous discharge medium
C313S565000, C313S637000, C420S559000
Reexamination Certificate
active
06404122
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a low-pressure mercury vapor discharge lamp provided with a discharge vessel,
which discharge vessel encloses a discharge space containing a filling of mercury and a rare gas in a gastight manner,
which discharge vessel contains an amalgam which is in communication with the discharge space,
and in which the low-pressure mercury vapor discharge lamp comprises discharge means for maintaining an electric discharge in the discharge vessel.
In mercury vapor discharge lamps, mercury constitutes the primary component for (efficiently) generating ultraviolet (UV) light. A luminescent layer comprising a luminescent material (for example, a fluorescence powder) may be present on an inner wall of the discharge vessel for converting UV to other wavelengths, for example to UV-B and UV-A for tanning purposes (sun panel lamps) or to visible radiation for general purposes of illumination. Such discharge lamps are therefore also referred to as fluorescence lamps. The discharge vessel of low-pressure mercury vapor discharge lamps is usually circular and comprises both elongated and compact embodiments. Generally, the tubular discharge vessel of compact fluorescence lamps has a collection of comparatively short straight parts of a comparatively small diameter, which straight parts are interconnected by means of bridge parts or via bent parts. Compact fluorescence lamps are usually provided with an (integrated) lamp base. In such embodiments of the low-pressure mercury vapor discharge lamp, the discharge means comprise electrodes which are arranged in the discharge space. An alternative embodiment comprises the electrodeless low-pressure mercury vapor discharge lamps.
The term “nominal operation” in the description and claims of the present invention is used for indicating operating conditions in which the mercury vapor pressure is such that the radiation output of the lamp is at least 80% of the output during optimum operation, i.e. under operating conditions where the mercury vapor pressure is optimal. The amalgam limits the mercury vapor pressure in the discharge vessel as compared with the discharge lamp containing only free mercury. This renders nominal operation of the lamp possible at comparatively high lamp temperatures such as may occur in the case of a high lamp load, or when the lamp is used in a closed or badly ventilated luminaire. Furthermore, the term “initial radiation output” in the description and claims is defined as the radiation output of the discharge lamp
1
second after switching on the discharge lamp and the “run-up time” as the time which the discharge lamp requires for achieving a radiation output of 80% of that during optimum operation.
A low-pressure mercury vapor discharge lamp as described in the opening paragraph, hereinafter also referred to as vapor pressure-controlled lamp, is known from U.S. Pat. No. 4,093,889. The mercury vapor pressure at room temperature is comparatively low in the known lamp. The known lamp thus has the drawback that, when it is operated on a conventional lamp supply, the initial radiation output is also comparatively low. Moreover, the run-up time is comparatively long because the mercury vapor pressure rises only slowly after switching on the lamp.
In addition to the amalgam lamps described above, low-pressure mercury vapor discharge lamps are known which do not only comprise a (main) amalgam but also an auxiliary amalgam. Provided that the auxiliary amalgam contains sufficient mercury, the lamp will have a comparatively short run-up time. Upon switching on the lamp, the auxiliary amalgam is heated by the electrode so that it evolves a substantial portion of the mercury present therein comparatively quickly. It is desirable that the lamp must have been out of operation for a sufficiently long time before switching on, so that the auxiliary amalgam has been able to take up sufficient mercury. If the lamp has been out of operation for a comparatively short period, the shortening effect on the run-up time is only weak. In addition, the initial radiation output is (even) lower than that of a lamp with a main amalgam only because the auxiliary amalgam sets a comparatively lower mercury vapor pressure in the discharge space. Furthermore, the drawback arises in comparatively long lamps that comparatively much time is required before the mercury evolved by the auxiliary amalgam has spread over the entire discharge vessel, so that such lamps show a comparatively bright zone near the auxiliary amalgam and a comparatively dark zone remote from the auxiliary amalgam for a few minutes after switching on.
Furthermore, low-pressure mercury vapor discharge lamps are known which are not provided with amalgam and contain exclusively free mercury. These lamps, hereinafter also referred to as mercury lamps, have the advantage that the mercury vapor pressure at room temperature and hence the initial radiation output are comparatively high. Moreover, the run-up time is comparatively short. Also comparatively long lamps of this type have an approximately constant brightness substantially throughout the length after switching on, because the vapor pressure (at room temperature) is sufficiently high upon switching on. Nominal operation at comparatively high lamp temperatures can be achieved with a mercury lamp whose discharge space contains (just) enough mercury to establish a mercury vapor pressure at the operating temperature, which mercury vapor pressure is close to the optimum mercury vapor pressure. During the lifetime of the lamp, however, mercury is lost because this is bound, for example, on a wall of the discharge vessel and/or on emitter material. In practice, such a lamp thus has only a limited lifetime. In mercury lamps, a quantity of mercury is therefore dosed which is considerably higher than the quantity required in the vapor phase during nominal operation. However, this has the drawback that the mercury vapor pressure is equal to the vapor saturation pressure associated with the temperature of the coldest spot in the discharge vessel. Since the vapor saturation pressure rises exponentially with the temperature, temperature variations which occur, for example, in a badly ventilated luminaire or in the case of a high lamp load, lead to a decrease of the radiation output. At comparatively low ambient temperatures, the mercury vapor pressure decreases, which also leads to a decrease of the radiation output.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a lamp low pressure mercury vapor discharge which, at least in regular use, has a comparatively high initial radiation output and a comparatively short run-up time, and also a comparatively high radiation output in a comparatively large range of ambient temperatures.
According to the invention, the amalgam has a bismuth-tin ratio (Bi:Sn) in the range of 20:80≦Bi:Sn≦80:20, a lead content (Pb) in the range of 0.7≦Pb≦12 at % and a mercury content (Hg) in the range of 0.05≦Hg≦2 at %.
An advantage of the use of such an amalgam is that, at room temperature, the mercury vapor pressure is comparatively close to that of liquid mercury. With said composition of the amalgam, the discharge lamp is nominally operated at a corresponding temperature of the coldest spot in the discharge vessel, ranging between comparatively wide temperatures of 65° C. to 140° C. A further advantage of the use of such an amalgam is that the curves at which the mercury vapor pressure is plotted as a function of the temperature can be adjusted via the mercury content and/or the composition of the amalgam. Said properties of the (main) amalgam, namely the broad temperature interval and the variable mercury vapor pressure curves are realized by the choice of the composition of the amalgam according to the invention. For the amalgams with a composition according to the invention, curves in which the mercury vapor pressure is plotted as a function of the temperature have a first stabilization range in the temperature range under the ternary Bi—Sn—P
Kaldenhoven Lambert C.I.
Keur Wilhelmus C.
Lankhorst Martijn H.R.
Niemann Ulrich
Van De Ven Marinus J.W.M.
Guharay Karabi
Halajian Dicran
Koninklijke Philips Electronics , N.V.
Patel Vip
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