Patent Application
20070145880
The invention relates to a low-pressure mercury vapor discharge lamp.
The invention also relates to a compact fluorescent lamp.
In mercury vapor discharge lamps, mercury constitutes the primary component for the (efficient) generation of ultraviolet (UV) light. A luminescent layer comprising a luminescent material may be present on an inner wall of the discharge vessel to convert UV to other wavelengths, for example, to UV-B and UV-A for tanning purposes (sun panel lamps) or to visible radiation for general illumination purposes. Such discharge lamps are therefore also referred to as fluorescent lamps. Alternatively, the ultraviolet light generated may be used for manufacturing germicidal lamps (UV-C). The discharge vessel of low-pressure mercury vapor discharge lamps is usually circular and comprises both elongate and compact embodiments. Generally, the tubular discharge vessel of compact fluorescent lamps comprises a collection of relatively short straight parts having a relatively small diameter, which straight parts are connected together by means of bridge parts or via bent parts. Compact fluorescent lamps are usually provided with an (integrated) lamp cap. Normally, the means for maintaining a discharge in the discharge space are electrodes arranged in the discharge space. In an alternative embodiment the low-pressure mercury vapor discharge lamp comprises a so-called electrodeless low-pressure mercury vapor discharge lamp.
In the description and claims of the current invention, the designation “nominal operation” is used to refer to operating conditions where the mercury-vapor pressure is such that the radiation output of the lamp is at least 80% of that when the light output is maximal, i.e. under operating conditions where the mercury-vapor pressure is optimal. In addition, in the description and claims, the “initial radiation output” is defined as the radiation output of the discharge lamp 1 second after switching on the discharge lamp, and the “run-up time” is defined as the time needed by the discharge lamp to reach a radiation output of 80% of that during optimum operation.
Low-pressure mercury-vapor discharge lamps are known comprising an amalgam. Such discharge lamps have a comparatively low mercury-vapor pressure at room temperature. As a result, amalgam-containing discharge lamps have the disadvantage that also the initial radiation output is comparatively low when a customary power supply is used to operate said lamp. In addition, the run-up time is comparatively long because the mercury-vapor pressure increases only slowly after switching on the lamp. Apart from amalgam-containing discharge lamps, low-pressure mercury-vapor discharge lamps are known which comprise both a (main) amalgam and a so-called auxiliary amalgam. If the auxiliary amalgam comprises sufficient mercury, then the lamp has a relatively short run-up time. Immediately after the lamp has been switched on, i.e. during preheating the electrodes, the auxiliary amalgam is heated by the electrode so that it relatively rapidly dispenses a substantial part of the mercury that it contains. In this respect, it is desirable that, prior to being switched on, the lamp has been idle for a sufficiently long time to allow the auxiliary amalgam to take up sufficient mercury. If the lamp has been idle for a comparatively short period of time, the reduction of the run-up time is only small. In addition, in that case the initial radiation output is (even) lower than that of a lamp comprising only a main amalgam, which can be attributed to the fact that a comparatively low mercury-vapor pressure is adjusted in the discharge space by the auxiliary amalgam. An additional problem encountered with comparatively long lamps is that it takes comparatively much time for the mercury liberated by the auxiliary amalgam to spread throughout the discharge vessel, so that after switching on such lamps, they demonstrate a comparatively bright zone near the auxiliary amalgam and a comparatively dark zone at a greater distance from the auxiliary amalgam, which zones disappear after a few minutes.
In addition, low-pressure mercury-vapor discharge lamps are known which are not provided with an amalgam and contain only free mercury. These lamps, also referred to as mercury discharge lamps, have the advantage that the mercury-vapor pressure at room temperature and hence the initial radiation output are relatively high as compared to amalgam-containing discharge lamps and as compared to discharge lamps comprising a (main) amalgam and an auxiliary amalgam. In addition, the run-up time is comparatively short. After having been switched on, comparatively long lamps of this type also demonstrate a substantially constant brightness over substantially the whole length, which can be attributed to the fact that the vapor pressure (at room temperature) is sufficiently high at the time of switching on these lamps.
In U.S. Pat. No. 5,274,305 the mercury vapor pressure in a low-pressure mercury discharge lamp is thermostatically controlled. The known low-pressure mercury discharge lamp includes electrodes and a source of mercury vapor sealed in a lamp envelope. A heater and a thermal switching device are in thermal contact with the source of mercury vapor. The heater is energized when the source of mercury vapor is below a predetermined temperature during operation of the lamp. Preferably, the heater is a resistance heater electrically connected in series with one of the lamp electrodes. The thermal switching device can be a bimetal thermostatic switch. The source of mercury vapor in the known low-pressure mercury vapor discharge lamp is typically an amalgam selected to have an optimum mercury vapor pressure at the maximum operating temperature of the lamp. The heater and the thermal switching device can be located external to the lamp envelope or can be located within the lamp envelope. The known low-pressure mercury vapor discharge lamp provides a relatively constant light output over a broad range of operating temperatures and different lamp orientations.
A relatively large amount of mercury is necessary for the known low-pressure mercury vapor discharge lamps in order to realize a sufficiently long lifetime. A drawback of the known discharge lamps is that they form a burden on the environment. This is in particular the case if the discharge lamps are injudiciously processed after the end of the lifetime.
The invention has for its object to eliminate the above disadvantage wholly or partly. According to the invention, a low-pressure mercury vapor discharge lamp of the kind mentioned in the opening paragraph for this purpose comprises:
a light-transmitting discharge vessel enclosing, in a gastight manner, a discharge space provided with a filling of mercury and a rare gas,
the discharge vessel comprising discharge means for maintaining a discharge in the discharge space,
the discharge vessel being provided with a source of mercury,
the discharge vessel being provided with a releasing means for the controlled release of mercury vapor from the source of mercury,
the releasing means being operative in response to a condition of the low-pressure mercury vapor discharge lamp,
the condition being a characteristic of the discharge lamp and/or a pre-determined time interval.
By providing a releasing means in the discharge vessel for the controlled release of mercury vapor from the source of mercury, the amount of mercury in the vapor phase in the discharge vessel during operation of the discharge lamp can be controlled during life of the discharge lamp. In addition, by making the releasing means responsive to a condition of the discharge lamp enables the discharge lamp to operate under unsaturated conditions during life of the discharge lamp. By measuring characteristics of the discharge lamp, the conditions for releasing mercury from the source of mercury can be set and the releasing means controls the amount of mercury vapor present in the discharge vessel during operation of the discharge lamp.
According to the invention, the condition which determines the release of mercury from the source of mercury is set by a characteristic of the discharge lamp and/or a pre-determined time interval. Operating the releasing means in response to a pre-determined time interval enables to gradually make available mercury during life of the discharge lamp. During life mercury is consumed in the discharge vessel, for instance in the glass and/or in the phosphor layer. This consumption of mercury resulting in less mercury being available for the maintenance of a discharge in the discharge vessel can be compensated by releasing some mercury into the discharge vessel during life of the discharge lamp at pre-determined times.
Operating the releasing means in response to a characteristic of the discharge lamp is a more sophisticated or “intelligent” means to enable the controlled release of mercury vapor from the source of mercury. The releasing means for the controlled release of mercury vapor can operate in response of the conditions in the discharge lamp.
Preferably the condition of the low-pressure mercury vapor discharge lamp is indicative of a content of mercury vapor in the discharge vessel below a pre-determined level. In a low-pressure mercury vapor discharge lamp operating under unsaturated condition, the mercury content is, preferably, higher than 0.02 mg Hg.
Preferably, the lamp characteristic is the arc characteristic of the discharge in the discharge vessel. Other lamp characteristics indicative of a reduced mercury content are a decreased lumen output of the discharge lamp, an increased infrared contribution to the lamp spectrum of the discharge lamp, a change in the lamp voltage, changes in the dynamic behavior of the discharge lamp and the occurrence of striations in the discharge lamp.
In the description and claims of the current invention, the designations “unsaturated” or “unsaturated mercury conditions” are used to refer to a low-pressure mercury vapor discharge lamp in which the amount of mercury dosed into the discharge vessel (during manufacturing) of the low-pressure mercury vapor discharge lamp is equal to or lower than the amount of mercury needed for a saturated mercury vapor pressure at nominal operation of the discharge lamp.
Operating a mercury vapor discharge lamp under unsaturated mercury conditions has a number of advantages. Generally speaking, the performance of unsaturated mercury discharge lamps (light output, efficacy, power consumption, etc.) is independent of the ambient temperature as long as the mercury pressure is unsaturated. This results in a constant light output which is independent on the way of burning the discharge lamp (base up versus base down, horizontally versus vertically). In practice, a higher light output of the unsaturated mercury vapor discharge lamp is obtained in the application. Unsaturated lamps combine a higher light output and an improved efficacy in applications at elevated temperatures with minimum mercury content. This results in ease of installation and in freedom of design for lighting and luminaire designers. An unsaturated mercury discharge lamp gives a relatively high system efficacy in combination with a relatively low Hg content. In addition, unsaturated lamps have an improved maintenance. Because the trends towards further miniaturization and towards more light output from one luminaire will continue the forthcoming years, it may be anticipated that problems with temperature in application will more frequently occur in the future. With an unsaturated mercury vapor discharge lamp these problems are largely reduced. Unsaturated lamps combine minimum mercury content with an improved lumen per Watt performance at elevated temperatures.
When the performance of unsaturated lamps is compared to so-called cold-spot or to so-called amalgam low-pressure mercury vapor discharge lamps the following advantages can be mentioned. In a “cold-spot” mercury discharge lamp, the mercury pressure is controlled by a so-called cold-spot temperature somewhere in the discharge vessel. In an amalgam mercury discharge lamp, the mercury pressure is controlled by means of an amalgam; in a number of such amalgam discharge lamps additionally an auxiliary amalgam is employed. The initial radiation output and the run-up time and ignition voltage of an unsaturated mercury discharge lamp are comparable to cold-spot lamps. Other properties like size (no cold-spot area necessary in an unsaturated discharge lamp; e.g. by introducing long stems), life time, color temperature, color rendering index and reliability are at the same level as known mercury discharge lamps. The maintenance of unsaturated lamps is expected to be better than that of the known compact fluorescent lamps (CFL) and fluorescent discharge lamps (TL). With unsaturated lamps miniaturization can be driven to its limits because thermal problems are minimized. For new installation unsaturated mercury discharge lamps this can result in a reduction of the total costs of ownership.
It is not an easy task to operate a low-pressure mercury vapor discharge lamp under unsaturated mercury conditions while simultaneously realizing a relatively long life of the discharge lamp. It is known that measures are taken in low-pressure mercury vapor discharge lamps to reduce the amount of mercury that during life of the discharge lamp is no longer able to contribute to the reactive atmosphere in the discharge space in the discharge vessel. Mercury is lost in that, due to the interaction of mercury and materials present in the lamp (such as glass, coatings, electrodes) and parts of the inner wall of the discharge vessel are blackened. Wall blackening does not only give rise to a lower light output but also gives the lamp an unaesthetic appearance, particularly because the blackening occurs irregularly, for example, in the form of dark stains or dots. Known measures to reduce the amount of mercury lost during life of the discharge lamp encompass special compositions of the glass of the discharge vessel, the application of protective coatings on the wall of the lamp vessel and electrode shields.
The measure according to the invention enables the manufacturing of long-life low-pressure mercury vapor discharge lamps which operate under conditions of unsaturated mercury content. Such unsaturated mercury discharge lamps have the advantage that the burden on the environment is reduced.
Several embodiments of the releasing means and sources of mercury can be realized. According to a preferred embodiment of the invention, a low-pressure mercury vapor discharge lamp of the kind mentioned in the opening paragraph is for this purpose characterized in that the releasing means is operated via a switch device. The switch device releases some mercury into the lamp vessel from the source of mercury. The switch device responds to a condition of the low-pressure mercury vapor discharge lamp indicative of a too low mercury vapor content in the discharge vessel.
Preferably, the switch device is mounted in the discharge vessel. In an alternative embodiment the switch device is mounted external to the discharge vessel.
According to a preferred embodiment of the invention, a low-pressure mercury vapor discharge lamp of the kind mentioned in the opening paragraph is for this purpose characterized in that the switch device comprises a reed relay. A reed relay is a well-known switch device in which current flowing in one circuit switches on and off a current in a second circuit. According to an alternative, preferred embodiment of the invention, a low-pressure mercury vapor discharge lamp of the kind mentioned in the opening paragraph is for this purpose characterized in that the releasing means is operated via an arc discharge. By way of example a controlled dc discharge, e.g. by means of a capacitor drained by the discharge, is created between the discharge electrode and the source of mercury.
Preferably, the source of mercury comprises at least one dispenser fiber comprising a mercury dispenser material. The releasing means may initiate a partial vaporization of the dispenser fibers while releasing mercury.
The mercury content in the discharge vessel can be expressed as the pressure of mercury in the discharge vessel of the low-pressure mercury vapor discharge lamp. According to a preferred embodiment of the invention, a low-pressure mercury vapor discharge lamp of the kind mentioned in the opening paragraph is for this purpose characterized in that the product of the mercury pressure pHg and the internal diameter Din of the discharge vessel is in the range 0.13≦pHg×Din≦8 Pa.cm. A discharge vessel of a low-pressure mercury vapor discharge lamp according to this preferred embodiment of the invention in which the product of the mercury pressure (expressed in Pa) and the internal diameter (expressed in mm) of the discharge vessel which is in the mentioned range from, contains a relatively low amount of mercury. The mercury content is considerably lower than what is normally provided for in known low-pressure mercury vapor discharge lamps. The low-pressure mercury vapor discharge lamp according to the second measure of the invention operates as a so-called “unsaturated” mercury vapor discharge lamp.
Preferably, the product of the mercury pressure pHs and the internal diameter Din of the discharge vessel is in the range 0.13≦pHg×Din≦4 Pa.cm. In this preferred regime of pHg×Din the mercury content in the discharge lamp is further reduced. In this preferred embodiment of the invention, the low-pressure mercury vapor discharge lamp according to the invention operates as an unsaturated mercury vapor discharge lamp.
A preferred embodiment of the low-pressure mercury vapor discharge lamp according to the invention is characterized in that the discharge vessel contains less than approximately 0.1 mg mercury. There is a tendency in governmental regulations to prescribe a maximum amount of mercury present in a low-pressure mercury vapor discharge lamp that if the discharge lamp comprises less than said prescribed amount allows the user to dispose of the lamp without environmental restrictions. If a mercury discharge lamp contains less than 0.2 mg of mercury such requirements are largely fulfilled. Preferably, the discharge vessel contains less than or equal to approximately 0.05 mg mercury.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
In the drawings:
The Figures are purely diagrammatic and not drawn to scale. Notably, some dimensions are shown in a strongly exaggerated form for the sake of clarity. Similar components in the Figures are denoted as much as possible by the same reference numerals.
In the example of
In the example shown in
Other lamp characteristics indicative of a reduced mercury content in the discharge vessel are a decreased lumen output of the discharge lamp (which can be measured via a output sensor), an increased infrared contribution to the lamp spectrum of the discharge lamp, a change in the lamp voltage, changes in the dynamic behavior of the discharge lamp and the occurrence of striations in the discharge lamp.
In the embodiment shown in
In an alternative embodiment of the melting process one of the vaporized metals serves as a (hydrogen/oxygen) getter.
In order to create the desired discharge an additional feed-through is created in the end portion 12a of the discharge vessel. An advantage of the switching scheme creating a vapor arc like discharge as shown in
In the compact fluorescent lamp as shown in
The first electrode 20a is provided at a second end portion referenced 41b of the tube referenced 41. The second electrode 20b is provided at a second end portion referenced 51b of the tube referenced 51. The second end portions 41b; 51b face away from the first end portions 41a; 51a. To obtain a relatively long electrode path, the electrodes 20a; 20b are arranged at extreme ends of the fluorescent lamp.
In the example of
The side of the tubes 41, 43; 45, 47; 49, 51 facing the discharge space is preferably provided with a protective layer (not shown in
Apart from the second end portions 41b; 51b provided with an electrode 20a; 20b, further second end portions 43b; 45b; 47b; 49b of the respective tubes 43; 45; 47; 49 are provided with a sealed end. Bridge parts 44; 48 for mutually connecting tubes 43, 45; 47, 49 of adjacent dual-shaped lamp parts 35, 36; 36, 37 are provided in the proximity of the second end portions 43b, 45b; 47b, 49b of the tubes 43, 45; 47, 49. At least one of the further second end portions 45b is provided with the source of mercury 7 and the releasing means 8.
In the example of
Operating a mercury vapor discharge lamp under unsaturated mercury conditions has a number of advantages. Generally speaking, the performance of unsaturated mercury discharge lamps (light output, efficacy, power consumption, etc.) is independent of the ambient temperature as long as the mercury pressure is unsaturated. This results in a constant light output which is independent on the way of burning the discharge lamp (base up versus base down, horizontally versus vertically). In practice, a higher light output of the unsaturated mercury vapor discharge lamp is obtained in the application. Unsaturated lamps combine a higher light output and an improved efficacy in applications at elevated temperatures with minimum mercury content. This results in ease of installation and in freedom of design for lighting and luminaire designers. An unsaturated mercury discharge lamp gives a relatively high system efficacy in combination with a relatively low Hg content. In addition, unsaturated lamps have an improved maintenance. Because the trends towards further miniaturization and towards more light output from one luminaire will continue the forthcoming years, it may be anticipated that problems with temperature in application will more frequently occur in the future. With an unsaturated mercury vapor discharge lamp these problems are largely reduced. Unsaturated lamps combine minimum mercury content with an improved lumen per Watt performance at elevated temperatures.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 03101913.6 | Jun 2003 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB04/50905 | 6/15/2004 | WO | 12/21/2005 |
