A lamp assembly

Abstract

 A lamp assembly incorporating fluorescent tubes for lighting purposes, and a voltage unit for applying an electric voltage over the tubes. According to the invention two or more fluorescent tubes ( 1- 6) are connected to the voltage unit (8) in series with one another. The voltage unit is constructed to deliver, during a tube ignition phase, a sufficiently high voltage with sufficiently high frequency to ignite the tubes (1 - 6) without requiring the heating of a device within the tubes, and which unit is construct­ed to deliver, subsequent to ignition of the tubes (1 - 6) a sufficiently high voltage with sufficiently high frequency to operate the ignited tubes (1 - 6).

Description

[0001] The present invention relates to a lamp assembly, and more specifically to a gas electric-discharge lamp assembly or fluorescent lamp assembly.

[0002] In known fluorescent lamp assemblies used for illumin­ating purposes there is used a so-called hot cathode tube, which for ignition purposes includes a cathode which is heated prior to ignition of the tube. Sub­sequent to ignition, the tube, or tubes, is (are) op­erated by applying an electric current of, for example 220V and 50Hz between the anode and the cathode. Heat­ing of the cathode and subsequent interruption of elec­tric current therethrough is effected, in a known man­ner, with the aid of a so-called starter. Known lamp assemblies of this kind also include a current limiting device in the form of a choke or ballast.

[0003] Lamp assemblies are known in the art which incorporate two tubes, both of which are served by a single common ballast. Lamp assemblies which incorporate three or more tubes include a respective starter and ballast for each tube. The thermal energy required to heat the cathode is simply lost, which is particularly negative when the lamp assembly is used, for example, in cara­vans, small watercraft, etc., where the electrical en­ergy utilized is obtained solely from a battery. The fact that electric energy is converted directly to thermal energy, which often needs to be dissipated, is also a negative factor when such lamp assemblies are powered from the general mains supply.

[0004] Another drawback associated with hot cathode tubes is that the cathode is consumed, resulting in a limited useful life of the tubes under normal use conditions.

[0005] A further drawback with hot cathode tubes is that they are difficult or impossible to ignite at low ambient temperatures. Consequently, such tubes are not used outdoors or, for example, in non-heated storage loca­tions where low temperatures can prevail in winter time.

[0006] The present invention relates to a lamp assembly with which the aforesaid drawbacks are avoided.

[0007] The present invention thus relates to a lamp assembly which incorporates fluorescent tubes intended for lighting purposes, and a voltage unit for applying an electric voltage across the tubes, and which is char­acterized in that two or more tubes are connected to said voltage unit in series with one another; in that the voltage unit is arranged to deliver, during a tube ignition phase, a voltage which is sufficiently high and of sufficiently high frequency to ignite the tubes without requiring the heating of a device within the tubes; and in that the voltage unit is arranged to deliver subsequent to ignition of the tubes, a suffi­ciently high voltage of sufficiently high frequency to operate the tubes.

[0008] The invention is based on the concept that by connect­ing a plurality of series-connected tubes to one and the same voltage unit it is possible to ignite and to operate all tubes, by applying a high voltage and high frequency to the series-connected tubes through said voltage unit.

[0009] It is previously known to ignite so-called cold cath­ode discharge tubes with a high frequency, high a.c. voltage. Cold cathode discharge tubes are provided with a large cathode over which a significant drop in voltage takes place. This results in significant iron losses and hence, in addition to the tube becom­ing hot in the region of the cathode, a substantial part of the energy supplied is dissipated in the form of thermal energy. When using cold cathode discharge lamps, for example neon lamps, each cold cathode tube is connected to a voltage unit. Since the available mains voltage is normally 110V and 60Hz or 220V and 50Hz, gas discharge lamps have hitherto exclusively taken the form of hot cathode lamps, in order to en­able the hot cathode tubes to be ignited.

[0010] The primary disadvantages with hot cathode discharge lamps is that a separate power unit is required for each of the tubes present even though, as mentioned above, two tubes may have components in common.

[0011] The present invention thus relates to a novel principle of igniting and operating the tubes of gas discharge lamps.

[0012] The invention is described in more detail hereinafter, partly with reference to exemplifying embodiments il­lustrated in the accompanying drawings, in which

Figure 1 illustrates a plurality of fluorescent tubes connected in accordance with the invention;

Figure 2 is a cross-sectional view of a lamp assembly;

Figure 3 illustrates one method of connecting up a tube of a conventional gas discharge lamp;

Figure 4 illustrates an alternative method of connect­ing up a tube of a gas discharge lamp.

[0013] Figure 1 illustrates a plurality of fluorescent tubes 6, which may be housed in casing 7 which partially embraces the tubes, vide Figure 2, to form a lamp as­sembly. The tubes 1 - 6 are connected to a voltage unit 8 which is constructed to apply an electric vol­tage across the tubes. The voltage unit 8 is connect­ed to a voltage source through terminals 9. This voltage source may comprise the standard mains netwok or a battery (accumulator), such as a vehicle battery, depending on the construction of the voltage unit 8.

[0014] In accordance with the invention two or more fluores­cent tubes are connected together in series and to said voltage unit. Thus, in Figure 1 a series cir­cuit thus formed comprises the one terminal 10 of the voltage unit 8, the tube 1, a conductor 11, the tube 2, a conductor 12, the tube 3, a conductor 13, the tube 4, a conductor 14, the tube 5, a conductor 15, the tube 6, and the other terminal 16 of the voltage unit 8. The voltage unit 8 is constructed to deliver, during the tube ignition phase, a sufficiently high voltage of sufficiently high frequency to ignite the tubes without needing to heat devices in the tubes.

[0015] The voltage unit is also constructed to deliver, sub­sequent to igniting the tubes, a sufficiently high voltage of sufficiently high frequency to operate the ignited tubes.

[0016] The voltage unit is preferably constructed to deliver the same, or substantially the same voltage and fre­quency during both the ignition phase and the operat­ing phase. This enables the voltage unit to be chosen from a large number of known and commercially avail­able units capable of being supplied with a direct current of, e.g., 12 Volts or an alternating current of 220 Volts/50Hz or 110 Volts/60Hz, and constructed to deliver a high voltage, e.g., 1000 - 10000 Volts, with a high frequency, e.g., of 1 - 100 kHz.

[0017] According to a preferred embodiment the voltage unit delivers a voltage higher than 500 Volts at a frequen­cy greater than 1 kHz.

[0018] It has been found beneficial to use a voltage of 900 - 4000V at a frequency of 10 - 100 kHz.

[0019] The voltage unit also incorporates a current limiting device for preventing voltage surges from occuring when the tubes are ignited.

[0020] When the voltage unit is supplied with direct current, the voltage unit is preferably one which will produce an alternating d.c. voltage of 10 - 50 kHz.

[0021] The invention shall not be considered to be limited to the use of a voltage unit of the aforesaid specifica­tion, however, since the qualifications "sufficiently high voltage" and "sufficiently high frequency" ex­pressed above naturally depend on the number of tubes used, the dimensions of the tubes, their rated effect, internal resistance, etc.

[0022] According to one preferred embodiment of the inven­tion, the lamp assembly includes at least three ser­ies-connected tubes connected to a voltage unit.

[0023] In this regard it is preferred, in accordance with the invention, to use conventional hot cathode discharge tubes in which the cathode is connected solely to one terminal. This is illustrated in Figure 3, which shows a conventional hot cathode tube 3 in which two connector pins 17, 18 are connected to the cathode. In this case only one conductor, 13, is connected-up, either to one pin, 17, or to both pins 17, 18. The conductor 12 is connected in a similar manner, as are all the conductors extending between respective tubes. Similarly, only one conductor 10;16 extends to the one end of the outermost tubes 1;6.

[0024] The present invention has surprisingly shown that a voltage source which delivers a relatively low voltage to each tube, e.g. a voltage of about 200V, at a high frequency is sufficient to ignite and operate a plur­ality of hot cathode fluorescent tubes connected in series.

[0025] An account of an experiment carried out in this regard is given below.

[0026] Ten hot cathode fluorescent tubes (Sylvania F8W/CW) were connected in series to a voltage unit in the man­ner illustrated in Figure 1, the voltage unit deliver­ing a voltage of 2000V with a frequency of 48kHz. The voltage of the voltage unit varied between 0V and +2000V. The voltage unit gave a maximum current strength of 20mA. Naturally, there is used a voltage unit which will limit the current strength in the ser­ies circuit to a value suitable for the fluorescent tubes concerned. There is thus no pre-heating of the cathodes when the tubes are connected up in this man­ner. No capacitors or other devices are used to hold a high voltage momentarily over a particular tube.

[0027] Corresponding experiments have been carried out for example with hot cathode luminescent tubes having a power rating of 25W, 40W, and 60W.

[0028] All tubes ignited practically instantaneously, when energising the voltage unit from a voltage source.

[0029] Long term tests have shown that very little heating of the tubes occurs when using a voltage unit having an output voltage which varies between 0V and a high d.c. voltage level. The ends of the tubes were still found to be at about room temperature after many hours of operation.

[0030] This enables the tubes to be placed in restricted spaces, without needing to provide effective air ex­change conditions in order to cool the tubes. One concrete advantage afforded hereby is that lamp fit­tings and assemblies for caravans, watercraft, etc, can be given small dimensions in relation to the fluorescent tubes, and can also be fitted into narrow and constricted spaces. In addition, the fact that only a small amount of heat is generated results in a lower total energy consumption, seen in the context of conventional gas discharge lamps which use fluorescent tubes, which is particularly beneficial when the only power supply available is a battery or accumulator.

[0031] Other tests in which the invention was applied have shown that the tubes will ignite instantaneously in ambient temperatures as low as -35°C.

[0032] This is a marked advantage, since it opens up new areas of use for lighting of this kind. Thus, lamps which incorporate the concept of the present inven­tion can be installed in unheated locations, cold storage locations, and in outhouses where very low ambient temperatures can be expected to prevail. By incorporating flashing devices in the series-circuit, the tubes can be extinguished and ignited at different frequencies, for example frequencies of from 0.25 to 5Hz. This is due to the fact that rapid ignition of the fluorescent tubes is obtained in lamps which in­corporate the concept of the present invention. Thus, the present invention enables fluorescent lighting to be used for the intermittent, or flashing illumina­tion of bill boards and traffic signals etc., some­thing which cannot be achieved with conventional hot cathode tube lighting, since ignition of the tubes is not instantaneous.

[0033] The above description has been given solely with ref­erence to the use of conventional hot cathode tubes. The reason for this is because such tubes are both inexpensive and readily available. It has also been found, however, that burnt-out hot cathode tubes will also ignite instantaneously and emit light with an intensity corresponding to that of new hot cathode tubes. All that is required to cause the tube to ig­nite and to emit light is the provision of an electric conductor at both ends of the tube.

[0034] According to a further embodiment of the invention, the conductors are not connected to the terminals of a hot cathode tube, but instead to electrically con­ductive plates 19, 20 or corresponding elements which are mutually spaced apart along the longitud­inal axis of the tube 21 and placed on the external surface thereof, as shown in Figure 4. Each of the plates 19, 20 is connected to its respective termi­nal by means of an allotted conductor 22, 23. The plates 19, 20 generate an electric field by means of which the tube can be ignited and operated. The tubes 21 of this embodiment are connected in series in accordance with the invention, in the manner described with reference to Figure 1, and a voltage unit of the aforesaid kind is used.

[0035] In accordance with one practical and inexpensive em­bodiment of the invention the plates 19, 20 consist of a piece of aluminium or copper foil attached to the outer surface of the tube. Alternatively, each plate may consist of aluminium or copper foil wrapped around the tube.

[0036] Naturally, in this regard hot cathode fluorescent tubes can be used, even though fluorescent tubes which totally lack connecting terminals may be used.

[0037] It will be appreciated that the useful life span of the tubes used is not contingent on a cathode which is progressively consumed with each ignition occasion, irrespective of which of the aforedescribed embodi­ments is used to connect-up the tubes. Consequently, the present invention affords the tubes a very long useful life. This also applies to hot cathode dis­charge tubes in which the cathodes have been consumed to such an extent that the tubes will not ignite when fitted in conventional hot cathode tube lamp assem­blies. A tube belonging to this latter character will still provide a very long burning time when used in accordance with the invention.

[0038] A number of advantageous applications have been men­tioned in the aforegoing. It will be appreciated, however, that the invention is particularly suitable for use in connection with indoor lighting, where the supply voltage to the voltage unit may be taken from the mains, i.e. 220V.

[0039] A particular advantage afforded by the lamp assembly according to the invention is that not all tubes are extinguished when the connection between two tubes is broken or when one tube fails to function, despite the tubes being series-connected in the manner il­lustrated in Figure 1. Assume that the conductors 11 and 12 are disconnected from the tube 2, or that the tube 2 is broken or faulty. In these events, the energy is switched between adjacent conductors as a result of the high frequency used. As a result, the tubes 4, 5, 6 will shine with substantially the normal degree of brightness, whereas the brightness of the tubes 1 and 3 will be lower, and the tube 2 is extin­guished.

[0040] Because only one single voltage unit is used, which for operating for example ten fluorescent tubes each at 8 watts has but small dimensions, the lamp assembly 7 may be given external dimensions which only slightly exceed the combined external dimensions of the tubes. In addition to the fluorescent tubes, the lamp fit­ting need only be large enough to accommodate hold­ers 24, 25 for holding the tubes in position, since the voltage unit 8 can be placed outside the lamp fitting. The term lamp assembly as used here, in the aforegoing and hereinafter is meant to include all types of lamp assemblies, lamp fittings and lamp furniture, such as lighting for interior and exterior illumination, billboards, etc. For example, a trans­parent billboard or advertising sign 26, or traffic sign may constitute the front side of the lamp. Such a lamp assembly, or lighting, is extremely neat and pre­sentable, and will illuminate the surface of the sign 26 very uniformly.

[0041] It will be clear from the aforegoing that all the aforesaid drawbacks are eliminated by means of the invention, which provides a particularly simple and advantageous lamp assembly which incorporates a plur­ality of fluorescent tubes, in which less energy is consumed and a longer span of utility is afforded in comparison wiht conventional lamps.

[0042] The invention shall not be considered to be limited to the aforedescribed embodiments thereof, since mod­ifications can be made within the scope of the follow­ing claims.

Claims

1. A lamp assembly incorporating fluorescent tubes for lighting purposes, and a voltage unit for applying an electric voltage over the tubes, charac­terized in that two or more fluorescent tubes (1 - 6) are connected to the voltage unit (8) in series with one another, in that the voltage unit is constructed to deliver, during a tube ignition phase, a suffi­ciently high voltage of sufficiently high frequency to ignite the tubes (1 - 6) without requiring the heating of a device within the tubes, and which unit is con­structed to deliver, subsequent to ignition of the tubes (1 - 6) a sufficiently high voltage of suffi­ciently high frequency to operate the ignited fluores­cent tubes (1 - 6).

2. A lamp assembly according to Claim 1, char­terized in that at least three fluorescent tubes (1 - 6) are connected in series to the voltage unit (8).

3. A lamp assembly according to Claims 1 and 2, characterized in that the voltage exceeds 500V and in that the frequency exceeds 1KHz.

4. A lamp assembly according to Claims 1, 2 or 3 characterized in that the fluorescent tubes (1 - 6) are of the hot cathode tube kind in which the cathode is connected solely to one terminal.

5. A lamp assembly according to Claims 1, 2 or 3, characterized in that each tube is provided with electrically conductive plates (19, 20) or the like arranged in mutual spaced relationship on the outer­surface of said tube (21) in the direction of the longitudinal axis thereof for the purpose of generating an electric field in said tube, each of said plates (19, 20) being connected to a respective terminal (22, 23).

6. An arrangement according to Claim 5, char­acterized in that the plates (19, 20) have the form of aluminium foil pieces or copper foil pieces which are attached to the outside of the tube 21.

7. An arrangement according to any of the pre­ceding claims, characterized in that the voltage unit (8) is constructed to limit the current strength through the series circuit to a value intended for the tubes (1 - 6; 21).

8. An arrangement according to any of the pre­ceding claims, characterized in that the voltage unit (8) is constructed to generate a voltage which varies between substantially 0 volts and a high voltage level, said variations taking place at a high frequency.

Drawing