FIELD OF THE INVENTION

The invention relates to a lighting device comprising a light source in the form of a cold cathode tube and a transparent tube which accommodates the light source.

BACKGROUND TO THE INVENTION

In various kinds of lighting, a number of different light sources in a number of different configurations are used. Especially in lighting on shelves and ledges for the illumination of goods on the shelves, various types of oblong light sources or fluorescent tubes are normally used. A ledge which is arranged on a shelf, for example, can be configured with partially transparent labels, which can themselves be back-lit with the aid of a light source, preferably an oblong light source or fluorescent tube, at the same time as any goods present on the shelf on which the ledge is arranged are illuminated.

In lighting of such a type, neon light sources, LED's and cold cathode tubes, CCFL, which stands for Cold Cathode Fluorescent Lamp, are normally used, for example. Fluorescent tubes of various types, such as, for example cold cathode tubes, are often relatively fragile and it is therefore usual for these to be used in connection with at least partially transparent plastic or glass tubes, in which the fluorescent tube is encapsulated in the tube. Typical of these fluorescent tubes is also that they have two connecting wires or conducting wires, which can be connected to a current or voltage source. These connecting wires or conducting wires are usually disposed at one end each of the fluorescent lamp for connection to a plus and minus pole, respectively, of a current or voltage source.

Light sources of the CCFL type have proved to have many advantages over, for example, LED's and neon light sources. On the one hand, they are relatively cheap compared with many other light sources, on the other hand they have a long service life and diffuse a good light. Another advantage is that they are relatively thin, which makes them suitable for use in restricted spaces, or for purely aesthetic reasons since a thinner fluorescent tube can look better than a larger and bulkier one.

A type of device with transparent tubes comprising cold cathode tubes is a transparent tube in which the two conducting wires of the cold cathode tube are each disposed at a respective end of the transparent tube, so that the transparent tube comprises a cord at the respective end of the transparent tube. Such a type is shown in Figure 1.

Another type of device with transparent tubes comprising cold cathode tubes is a transparent tube in which one conducting wire of the cold cathode tube is led back in the transparent tube so that both conducting wires of the cold cathode tube are disposed at one and the same end of the transparent tube, so that the transparent tube has a cord, comprising both conducting wires, or two cords, a cord for each respective conducting wire, only at a single end. Such a type is shown partially in Figure 2. US 2006/0273738 Al also gives an example of such a type of device.

In cramped spaces and under other conditions, a device having one or two cords only at a single end of the tube is preferable. This can be due to a variety of factors, for example that the installation is made easier.

In such devices, the length of the two cords or conducting wires can be important to the optimal working of the cold cathode tube. We denote the length of the first conducting wire as L ₁ and the length of the cold cathode tube as L ₂ , and the length of the second conducting wire as L ₃ . For optimal working of the cold cathode tube, the length of the cold cathode tube plus the length of the second conducting wire must substantially correspond to the length of the first conducting wire, or expressed mathematically L ₁ = L ₂ + L ₃ . Typically, it is desirable that it should differ by no more than 10 mm.

Precisely the type of device having one cord or two cords only at one end of the tube is associated with a few drawbacks due to its design, which drawbacks can lead to serious functional problems. Moreover, these have been shown to be aggravated, the greater the length of the tube or the device. Especially with lengths above 350 mm, the risk of occurrence of these drawbacks increases. Since lengths of up to 1 metre are common, these drawbacks and functional problems can be extremely apparent.

The conducting wires are made of an electrically conductive material, which generally makes the conducting wires bendable, but still relatively rigid. The result is that it is not easy to get them to lie fully straight, which is important with regard to the conducting wire running in the same cavity or channel in the transparent tube as the cold cathode tube itself. Since the conducting wire cannot be tensioned in any way tightly without risk of it being damaged or snapping, especially when fastened to the cold cathode tube, the conducting wire will lie in a slight zigzag or irregular pattern. This means that it is difficult to fulfil the equation above, L ₁ = L ₂ + L ₃ , since the conducting wire then becomes slightly longer than if it were to lie fully straight inside the tube.

Since the conducting wire runs in the same cavity or channel in the transparent tube as the cold cathode tube itself, the conducting wire lies extremely close to the cold cathode tube. This can cause electromagnetic disturbances inside the cold cathode tube, which can result in the light of the cold cathode tube becoming uneven and flickering. This is an effect of the conducting wire being slightly zigzagged, as it causes the distance between the cold cathode tube and the conducting wire to vary, which can generate these disturbances.

Another drawback which can arise is that the conducting wire bears against the cold cathode tube at one or more points, which is also an effect of the conducting wire being slightly zigzagged. These points of contact can produce lasting damage to the cold cathode tube.

A further drawback is that the cold cathode tube experiences higher heat development than normal, especially at the points where the conducting wire bears against the cold cathode tube.

Yet another drawback is that the total working life of the cold cathode tube is considerably reduced.

In addition, another drawback is that certain types of conducting wires acquire electrodeposits. This can result in impaired conductivity, shortened working life and, by extension, breakage of the conducting wire. Moreover, the wire blocks out some of the light from the cold cathode tube, especially when it lies in a slight zigzag or irregular pattern.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved lighting device comprising an elongated cold cathode tube accommodated in an at least partially transparent tube.

Another object of the invention is to provide a device of this kind which allows lighting with a disturbance-free and flicker-free light, including with relatively long cold cathode tubes.

A further object of the present invention is to provide a device of this kind with which the working life of the cold cathode tube can be prolonged in relation to previously known devices.

Yet another object of the invention is to provide a device of this kind which is both simple to produce and install and is safe and durable.

These and other objects are met with a lighting device of the type which is defined in the preamble to Patent Claim 1 and which has the specific technical distinguishing features defined in the characterizing part of the claim. The lighting device according to the invention comprises an elongated cold cathode tube, which cold cathode tube has a first and a second end and a first and a second conducting wire, connected to the cold cathode tube on the first and second end respectively, for connecting the cold cathode tube to a current or voltage source, which device further comprises an at least partially transparent tube having a first and a second tube end for the enclosing reception of the cold cathode tube, the said tube being configured in one piece, which forms a radially enclosed conducting wire channel arranged to receive the first conducting wire of the cold cathode tube, and a light source channel arranged to receive the cold cathode tube, which channels extend between the first tube end and the second tube end.

One advantage of the invention is that the conducting wire is spatially separated from the cold cathode tube, which means that the conducting wire cannot come into contact with the cold cathode tube. The distance between the cold cathode tube and the first conducting wire can hence be kept constant. This has the advantage that the first conducting wire can be kept substantially straight, which improves the conditions for fulfilling the equation L ₁ = L ₂ + L ₃ .

The one-piece configuration of the tube forming the conducting wire channel and the light source channel allows the total number of components of the lighting device to be kept low. Because the conducting wire channel is radially enclosed, the first conducting wire is protected in a simple and effective manner. Moreover, that shape of the tube which radially encloses the conducting wire channel helps to keep the first conducting wire constantly in a well-defined position and at a constant distance from the cold cathode tube along the full length of the conducting wire channel.

A further advantage of the invention is that it is easier to use long devices comprising long cold cathode tubes.

One advantage is that the risk of electromagnetic disturbances is markedly reduced, which means that the light becomes more even and with reduced flicker. Another advantage is that the cold cathode tube experiences reduced heat development and that the risk of the first conducting wire acquiring electrodeposits is reduced, since the conducting wire cannot come into contact with the cold cathode tube at one or more points.

The conducting wire channel expediently extends substantially parallel with the light source channel. A device comprising a cold cathode tube is generally installed on a mounting surface such as a wall, a shelf or the like. In other words, the cold cathode tube does not generally diffuse light over 360° radially. One advantage of the conducting wire channel extending substantially parallel with the light source channel is that the device can be installed such that the conducting wire channel faces towards the mounting surface along the whole of its length.

The light source channel is expediently radially enclosed by the one-piece tube. The cold cathode tube is hence also protected in a safe, simple and effective manner.

The lighting device expediently comprises a protective casing, which is configured to constitute an end plug for the second end of the tube and to lead both conducting wires of the cold cathode tube through the protective casing. One advantage of a protective casing of this kind is that dirt, dust, insects, moisture, etc., which can be harmful to the cold cathode tube or which can impair its function, are prevented from penetrating into the device or the tube .

The protective casing is expediently further configured to allow both conducting wires of the cold cathode tube to be contained in one or two insulating cords for connection to a current or voltage source. Since the cold cathode tube is driven by high voltages, it is a clear advantage that the conducting wires are insulated between the device itself and the current or voltage source.

The conducting wire channel is expediently equally as long as the light source channel, these channels extending from the first end of the tube to its second tube end. The production of the tube is thereby facilitated, which tube can then be wholly produced by a simple compression moulding or extrusion operation.

According to one embodiment of the invention, the conducting wire channel is somewhat shorter than the light source channel. One advantage of the conducting wire channel at the first end of the tube being somewhat shorter than the light source channel is that the device can be made somewhat shorter. Where the conducting wire channel and the light source channel are equal in length at the first end of the tube, it may be necessary for the first conducting wire to project slightly beyond the first tube end when the first conducting wire extends from the first end of the cold cathode tube to the conducting wire channel. If the conducting wire channel is somewhat shorter than the light source channel, the conducting wire does not need to project beyond the first end of the tube.

The device according to the invention expediently also comprises a closure plug, which is configured to seal the first end of the tube. The closure plug can have several functions and advantages. It protects the cold cathode tube from external factors, such as dust, moisture, insects, etc., which can be harmful to the cold cathode tube or which can disturb the light flux from the cold cathode tube. According to the invention, the closure plug expediently comprises a closure portion and a plug-in portion, in which the plug-in portion is configured to be insertable into the light source channel of the tube and the closure portion is configured to close off the first end of the tube.

The device according to the invention also expediently comprises at least one 0-ring, which 0-ring is arranged to enclose the cold cathode tube and, in contact with the inner wall of the light source channel, to support the cold cathode tube in the light source channel. One advantage of one or more 0-rings which support the cold cathode tube in the light source channel is that the cold cathode tube is protected against vibrations and shocks which might otherwise damage the cold cathode tube. Vibrations and shocks can typically arise as the device is being transported or if it is mounted on an object which, in itself, can generate shocks and vibrations. With the aid of the O-ring(s), a centred securement of the cold cathode tube in the light source channel is also achieved in a cheap and simple manner.

Further objects or advantages of the invention emerge from the following detailed description of illustrative embodiments and of the patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a first lighting device according to the prior art.

Figure 2 is a perspective view of a part of a second lighting device according to the prior art.

Figure 3a is a perspective view of a part of a lighting device according to a first embodiment of the invention. Figure 3b is a longitudinal section through the lighting device shown in Fig. 3a.

Figure 3c is a longitudinal section corresponding to that in Fig. 3b and shows the lighting device supplemented by a protective casing on one end.

Figure 4 is a longitudinal section, corresponding to that in Fig. 3b, of a lighting device according to a second embodiment .

Figure 5 is a perspective view of certain parts of the lighting device shown in Figs. 3a, 3b and 3c and supplemented by an end-closure plug.

Figure 6 is a cross section through a part belonging to the lighting device shown in Figs. 3a, 3b, 3c and 5.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described with the aid of a few exemplary embodiments of the invention, with reference to the accompanying drawings. It should be pointed out, however, that the invention is not limited to the embodiments which are described here, but rather these should be regarded as an aid for illustrating and understanding the invention.

When a cold cathode tube is used, this normally involves connecting a rectifier to the mains electricity network, which has a voltage of about 230 V. Arranged after the rectifier is an inverter, which transmits alternating voltage of about 600- 1000V and at about 25 kHz. These components are not shown in the figures. The voltage required to drive the cold cathode tube is dependent on its length, the longer the cold cathode tube, the higher the voltage. When reference is hereinafter made to connecting to a current or voltage source, the allusion is to the inverter or similar device which provides the cold cathode tube with the necessary voltage at the necessary frequency. What is also unapparent from the drawings is that the conducting wire is usually made of copper and nickel and is coated with a thin, non-insulating surface layer. A cold cathode tube further comprises a mixture of the gases Argon and Neon, plus mercury vapour and an inner coating of, for example, phosphorous.

Figures 1 and 2 show a couple of devices according to the prior art. Figure 1 shows a standard type of device, having a transparent tube comprising a cold cathode tube, in which the two conducting wires of the cold cathode tube are each arranged on a respective end of the transparent tube, so that the transparent tube comprises a cord at the respective end of the transparent tube. Figure 2 shows another standard type of device having a transparent tube comprising a cold cathode tube, in which one conducting wire of the cold cathode tube is led back in the transparent tube so that both conducting wires of the cold cathode tube are arranged on one and the same end of the transparent tube, so that the transparent tube has a cord or two cords only at a single end. In the case of the device shown in Figure 2, the device usually comprises at its second end an end plug, which is not shown in the figure.

Figure 3a shows a device according to an exemplary embodiment of the invention, viewed obliquely from a first end 7. Figure 3b shows the same device in longitudinal cross section, viewed from the side. The device 1 comprises a transparent tube 2, which tube has a first tube end 7 and a second tube end 8. As can most clearly be seen from Figs. 3a and 6, the tube 2 is configured in one piece. The tube 2 forms or defines a radially enclosed light source channel 4 and a likewise radially enclosed conducting wire channel 5. In the light source channel 4 there is arranged an elongated cold cathode tube 3. The cold cathode tube 3 has a first end 10 and a second end 11. On the first end 10 of the cold cathode tube there is arranged a first conducting wire 6, and on the second end 11 of the cold cathode tube there is arranged a second conducting wire 9 • These two conducting wires 6 , 9 are intended to be connected to a current or voltage source in order to supply current or voltage to the cold cathode tube 3. Figures 3a and 3b also show how the first conducting wire 6 of the cold cathode tube 3 extends from the first end 10 of the cold cathode tube to the conducting wire channel 5, and through this towards the second end 8 of the tube 2.

In this way, the first conducting wire 6 cannot come into contact with the cold cathode tube 3, which means that all drawbacks associated with the first conducting wire 6 coming into contact with the cold cathode tube 3 at one or more points are hereby eliminated.

Figures 3a and 3b also show that the light source channel 4 and the conducting wire channel 5 extend substantially parallel with each other.

Figure 3c shows the same device 1 as Figures 3a and 3b. Figure 3c also shows the device 1 provided with a protective casing 12 on the second tube end 8, in which the protective casing 12 allows both conducting wires 6 and 9 of the cold cathode tube 3 to run through the protective casing 12. Figure 3c also shows how the protective casing 12 is configured to constitute an end plug for the second tube end 8 of the tube 2. The protective casing 12 is also configured to allow both conducting wires 6 and 9 of the cold cathode tube to be contained in two insulated cords for connection to a current or voltage source (not shown). This is illustrated in Figure 3c with the aid of two cords 13 and 14.

Figure 4 shows an alternative embodiment of the tube 2 of the device 1. In this embodiment too, the tube is configured in one piece, but the conducting wire channel 5 is somewhat shorter than the light source channel 4 on the first end 7 of the tube 2.

According to this embodiment, the conducting wire channel 5 is advantageously between 2 and 10 mm shorter than the light source channel 4 on the first end 7 of the tube 2. The fact that the conducting wire channel 5 is somewhat shorter than the light source channel 4 allows the first conducting wire 6 to extend from the first end 10 of the cold cathode tube 3 to the conducting wire channel 5 within the tube 2. This can be advantageous in a situation in which the cold cathode tube 3 and the tube 2 are substantially equal in length and in which the device is to be installed in a space which is limited in the longitudinal direction.

Figure 5 shows in simplified representation the device 1 shown in Figs. 3a and 3b, viewed from the first end 7, comprising the tube 2. The tube 2 comprises the light source channel 4 and the conducting wire channel 5. In Figure 5, however, the cold cathode tube itself has been omitted for the sake of simplicity. Figure 5 shows a closure plug 15, which is configured to seal the first end 7 of the tube. This closure plug 15 can have several functions. It is desirable to protect the cold cathode tube from external factors, such as dust, moisture, etc., which can be harmful to the cold cathode tube 3 or which can disturb the light flux from the cold cathode tube 3. The closure plug 15 consists of a closure portion 16 and a plug-in portion 17. The closure portion 16 has the function of sealing the first end 7 of the tube 2 and the plug-in portion 17 is configured to be insertable into the light source channel 4 of the tube 2.

The closure plug 15 can have several different embodiments, which depend to some extent on which of the two embodiments of the conducting wire channel 5 which are described here is at issue. In the first embodiment, in which the conducting wire channel 5 is equally as long as the light source channel 4 and the tube 2, the first conducting wire 6 extends partially beyond the tube 2. This is shown in Figures 3a, 3b and 3c. In such an embodiment, the closure plug 15 is configured to allow the first conducting wire 6 to extend beyond the tube 2 itself. The closure portion 16 is configured with an inner cavity for receiving that part of the first conducting wire 6 which extends beyond the tube 2. This can be achieved, for example, by configuring the closure portion 16 substantially as a hemisphere, as shown in Figure 5. Another example is to configure the closure portion 16 as a cylindrical portion having an inner cavity which allows the first conducting wire

6 to extend beyond the tube 2, from the first end 10 of the cold cathode tube 3 to the conducting wire channel 5. In this embodiment with conducting wire channel 5 equally as long as the light source channel 4, the plug-in portion 17 must also be configured with regard to the first conducting wire 6 and the conducting wire channel 5. The plug-in portion 17 is expediently configured as a substantially cylindrical portion having a cross section consistent with the cross section of the tube 2. The plug-in portion 17 is configured, however, with a groove 18, which allows the conducting wire channel 5 to fit into the groove 18 to allow the first conducting wire 6 to extend beyond the tube 2 itself. In the alternative embodiment shown in Figure 4, in which the conducting wire channel 5 is somewhat shorter than the light source channel 4 on the first end 7 of the tube 2, the same closure plug 15 can be used as in the embodiment which has just been described. However, the closure portion 16 can be configured as a plate (not shown), since the first conducting wire 6 does not extend beyond the tube 2. The closure portion

16 does not therefore need to be configured to accommodate the first conducting wire 6. If the plug-in portion 17 is longer in the longitudinal direction than the difference in length between the conducting wire channel 5 and the light source channel 4, regard must be given, in similar fashion to previously described, to the conducting wire channel 5, and a groove 18 is configured in the plug-in portion 17. If the plug-in portion 17 has a length in the longitudinal direction which is maximally as long as the size of the difference between the length of the light source channel 4 and the length of the conducting wire channel 5, the plug-in portion

17 does not need to be configured with any groove for the conducting wire channel 5.

In both the above-described embodiments, the plug-in portion 17 is expediently configured with an inner diameter which substantially conforms to the outer diameter of the cold cathode tube. The plug-in portion 17 can hereby effect securement of the cold cathode tube, so that this is centred in the light source channel. The protective casing 12 shown in Fig. 3c also expediently comprises a corresponding plug-in portion (not shown) in order to effect centred securement of the cold cathode tube in the light source channel on the corresponding end of the transparent tube. The device 1 advantageously also comprises at least one 0-ring 19. This or these O-ring(s) is/are arranged to enclose the cold cathode tube 3 and, in contact with the inner wall of the light source channel 4, to support the cold cathode tube 3 in the light source channel 4.

The O-ring(s) is/are preferably at least partially- transparent, so as to be minimally visible and block off the light from the cold cathode tube (3) as little as possible.

Even though the invention has been described on the basis of a few exemplary embodiments, these are not limiting for the invention. As a few examples can be mentioned that the at least partially transparent tube does not need to have a circular-cylindrical shape. The tube can, for example, have an oval, square or rectangular cross section, or other cross section.