The invention relates to a lighting unit in which the gasdischarge vessel consists of two or more adjacently situated tubular elements ("legs") connected by means of a so-called bridgeconstruction and where between these legs an electrically conductive element is being placed which is galvanicly connected with one of the electrodes (filaments) of the gasdischarge lamp, preferably via a high-ohmic electrical resistor, where this conductive element functions as an additional help for ignition of the lamp and can be used also for light reflection purposes.

Similar arrangements are generally known in fluorescent lamps and are being applied as an additional help for ignition purposes. In those special tubular fluorescent lamps an electrically conductive strip is fixed to the inner side of the glass wall of the discharge tube and is electrically connected with one of the electrodes of the lamp.

An other variant relates to the electrically connecting of metal parts of lighting luminaries with one electrode of a fluorescent lamp in order to improve the ignition behaviour of these lamps . This construction is only feasible in those cases where the luminarie is electrically grounded. The maximum allowable distance between lamp and luminarie is determined at 0.5 inch.

The technological evolution of fluorescent lamps has made great progress in the past decade, particularly driven by needs of energy-saving in lighting applications where incandescent lamps where applied. This relates to those applications in the light output range of 150- 1500 lumens.

Successful examples of this development in energy-saving alternatives in this low lumen range from 150- 1500 lumens are the so-called PL and PLC lamps. Basically they consists of two (PL) or four (PLC) adjacent gasdischarge tubes, connected by a bridge-construction.

It is self-evident that the total physical length of the tubular fluorescent lamp can be shortened by a factor 2 for PL and a factor 4 for the PLC types. A generally accepted

terminology for this types of lamps is "compact- fluorescent- lamps" (CFL). Manufacturers of these types of lamps use codes like PLC, BIAX, BB-2 and Double-Twin.

For ballasting purposes of these compact-fluorescent lamps one can choose for the classical electromagnetic solution, consisting of an electromagnetic coil in combination with an ignitor (glow-switch or electronic) . An other option for ballasting these lamps is an electronic ballast, offering a number of additional advantages, such as higher efficiency, smaller dimensions, lower weight, improved power-factor and a better control of the lamp current. A major drawback is the fact that electronic ballast's are a few times more costly than the electromagnetic ballast's.

Designing electronic ballast circuitry for compact fluorescent lamps one would prefer circuitry with the characteristics of a current source because of the specific impedance of the gas discharge lamp (negative impedance). An electrical circuit of the so-called "down-convertor" type is the most simple solution with respect to the number of required electrical components. In the combination of a compact fluorescent lamp and a down-convertor ballast type the lamp current is running from cathode to anode in only one direction (uni-directional current). The inner diameter of the glass tube should be chosen sufficiently large so that the recombination of charged particles in the gasmixture will not be disturbed. Practical experiments have shown that an inner diameter of the glass tube higher than 14.5 millimeters is adequate for compact fluorescent lamps in the lumen range from 150- 1500 lumens. An additional benefit of choosing this diameter is that depreciation of light output in "over-powering" conditions, due to excessive heating of the glass, is less than with commonly used 10 millimeter glass tube diameters.

In most cases the electrical properties of an electrical circuit from the down convertor type are not sufficient to guarantee reliable ignition of the lamp.

It is a general object of this invention to provide an electrically conductive element that is placed between the legs of a plural folded gasdischarge lamp i.c. a compact fluorescent lamp, and is galvanicly connected with one of the electrodes of the lamp, by which the ignition behaviour of the lamp is substantially improved without the need for additional electronic circuitry.

This element can be a metal plate or a plastic element with electrical conductive coating on one or both sides of the plastic material. This plastic material can be chosen as transparent or non-transparent. In case of a non-transparent element the gasdischarge vessel is optically separated into two identical parts. For purposes of light reflection of a luminarie the non-transparent element can be used as part of the optical system.

It is an object of the invention that the area of the conductive element can be chosen relatively large by which the ignition behaviour of the lamp- ballast system can be improved substantially. In most applications no additional electric circuitry is needed for reliable ignition which means an enormous advantage over state-of-the-art electronic ballast's. This means that the lamp- ballast system according to this invention can compete with the classical electromagnetic ballast's on a costprice-basis and potentially can mean that a break-through is possible in those applications where energy saving lighting systems are hampered by costs. Prototypes, where the area of the conductive element was up to six times higher than the physical dimensions of the lamp has proven to be very successful.

It is another object of the invention to use a printed-circuit-board laminate as the conductive element.

By choosing sufficient area the electrical capacitance of the element will have the right value to integrate the ignitionhelp function of the conductive element with the function of ignition-capacitor in the down-convertor circuit. In this case the element is electrically connected between the two electrodes of the lamp.

An other special feature of the invention is the encapsulation of the electronic circuitry by a potting compound, where because of superior thermal conductive properties with respect to air (>20 times), the lifetime of the electronic components can be extended by a factor of two or three.

A special execution of the invention relates to a combination of a compact fluorescent lamp with an electronic ballast from the down convertortype, where the electronic components are encapsulated by a potting compound in which ilmenitesand is applied as one of the filler materials.

Measurements have shown that this combination has a positive effect on the regulation characteristics of the autonomous nervous system of persons that are exposed to the radiation of this lamp. In this respect optimal results are made, using the lamptype "Mitsubishi BB-2, FDL9 G and FDL18 G".

The invention will be illustrated with figures that shows the dimensional placing of the conductive element in the front view of the gas discharge vessel of compact fluorescent lamps: In figure 1 the electrically conductive element "1" is pointed out as AA'. The main function of the element in this situation is to improve ignition performance in the combination of compact fluorescent lamp and down convertor ballast. The optical function for light reflection purposes is relatively small and in case of a transparent conductive element does not exist. The legs of the plural folded gas discharge vessel are indicated with "2" while the electrodes of the lamp are indicated by "E".

In figure 2 the electrically conductive element "1" is pointed out by BB'. In this case the element will function as an effective ignition antenna because of the relatively large area, but in the second place functions as part of the optical system. The lamp is split up in two identical parts where each part can be handled separately for light reflection purposes. The legs are indicated by "2" and the lampelectrodes by E".

In the figures 3 and 4 the invention is illustrated for two-legs lampconstructions (PL). The meaning of the indices are equivalent as in figures 1 and 2.

In figure 5 a special construction of the conductive element "1" , where the optical part of the functions is minor , but the hollow inner side "H" of the element "1' can be used as an injection-nozzle for the encapsulation of the electronic components by a compound. It is obvious that the room inside "H" can also be used to position one or more electronic components of the electronic ballast circuitry.