STATE OF THE ART Lamps and other current consuming electric devices having recharge- able batteries are used to an ever increasing extent. Substantially, this de- pends on the fact that such batteries have become better in different as- pects. In some types of devices, e. g. electric torches, it is common that the batteries must be removed from the device in connection with charging. To avoid this disadvantage, also electric devices have been developed in which the batteries can be charged through specific connecting devices on the out- side of the devices.

However, surface mounted connecting means cause several disad- vantages in itself. One important disadvantage is the risk that the batteries are discharged, e. g. by the connecting means being short-circuited. The possibilities to obtain a confined and level surface of a housing surrounding the device are also reduced.

SUMMARY OF THE INVENTION One object of the invention is to obtain a rechargeable lamp being de- void of the above mentioned disadvantages. This object is achieved by the invention having the features of claim 1. The lamp according to the invention comprises a set of conventional accumulators and lighting means connected thereto. In a preferred embodiment, the entire lamp is surrounded by a wa- terproof housing.

The charging current necessary to charge the accumulators is con- ducted from a charging device through a specific transfer means, which transfer means comprise a plurality of interacting coils. Energy is transferred from a primary coil connected to the charging device to a secondary coil connected to the accumulators through induction. The transfer takes place entirely without any galvanic connection, wherein the risk of short-circuiting is completely eliminated.

By arranging one or more primary coils in a rod-shaped carrier, one or more rechargeable lamps can be charged by bringing the lamps onto the carrier, wherein a secondary coil arranged in each lamp is positioned close to a primary coil of the carrier. The charging may be started automatically when the lamp is correctly positioned on the carrier.

For switching on and switching off the lamp, an electric switch is ar- ranged within the housing of the lamp. The location results in a low risk for short-circuiting. The entirely enclosed design of the lamp implies that the lamp can be placed in water, e. g. in a bath tub, without any risk. The lamp may also be placed in other environments and may be provided with an indi- vidual and attractive external design.

Further advantages and features of the invention is evident through the description, drawings and dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with the aid of ex- emplary embodiments and with reference to the accompanying drawings, in which Fig. 1 is a schematic perspective view of one embodiment of a lamp according to the invention, Fig. 2 is a schematic longitudinal section view of the carrier in Fig. 1 and five lamps positioned thereon, and

Fig. 3 is a principal circuit diagram of an electric circuit included in the lamp according to Fig. 2.

DESCRIPTION In the embodiment of a lamp according to the invention shown in Fig.

1, a lamp 10 is positioned in a combined carrier and charging device 11. The carrier 11 is designed as a rod 12, which is projecting from a base plate 13.

In the embodiment shown, the rod is designed with a circular cross section.

The length of the rod 12 is selected, so that a plurality of lamps, suitably at least four, can be brought onto the rod. The lamps rest directly on each other on the carrier. An indicator means 14, which is designed as a light emitting diode in the embodiment shown, is arranged on the top of the rod 12 to indi- cate that charging of a lamp is in progress.

Fig. 2 shows a charging of five lamps 10 simultaneously on the charg- ing device 11. The bottom lamp 10 is resting upon the base plate 13 and the remaining lamps are resting upon the adjacent underlying lamp. Each lamp 10 comprises lighting means 15 and accumulator means 16. The lighting means may be designed as light emitting diodes having high lighting effect.

In one embodiment the light emitting diodes are arranged as seven sets connected in series, each set comprising four light emitting diodes connected in parallel. The accumulator means 16 may comprise three nickel-cadmium cells connected in series. The connection of the electric components ap- pears in more detail with reference to Fig. 3.

The transfer of charging current to the accumulator means 16 of a lamp takes place through a secondary coil 17 arranged in the lamp and a primary coil 18 arranged in the rod 12. One primary coil 18 is arranged for each lamp, so that charging of all of the lamps on the rod can take place si- multaneously. The primary coils 18 are recessed in ring-shaped grooves in the envelope surface of the rod and the secondary coils will be surrounded by the corresponding primary coil when a lamp is positioned on the rod.

Hence, the induction between the primary coil and the secondary coil be- comes effective.

The primary coils 18 are connected in parallel and are operated by a 30 V peak-to-peak voltage at a frequency of 150 kHz. The driving voltage is obtained from a conventional power supply and is not described further.

Other configurations of the primary coil and the secondary coil are also pos- sible within the scope of the invention.

The circuit diagram of Fig. 3 discloses an implementation of the elec- tric circuit in a lamp 10 and its inductive connection to the charging means 11 and a power supply 19. In the embodiment shown, five primary coils 18 con- nected in parallel are included. The secondary coil 17 of a lamp is connected to a first voltage regulator 20, wherein suitable voltage may be applied to the three cells of the accumulator means 15. Using three standard cells 4.2 V is a suitable voltage. The first voltage regulator 20 also limits the charging cur- rent. A suitable charging current is 200 mA, resulting in a charging time of 10 hours for a full charge.

When a lamp is positioned on the charging device a voltage is induced in the secondary coil 17. The voltage is detected by a circuit breaking means 21 connected to the secondary coil. In a simple embodiment the circuit breaking means comprises a transistor, which is blocked upon detection of a voltage. The circuit breaking means 21 prevents supply of current to the lighting means 15 while charging is in progress.

When a lamp is removed from the charging device, the voltage over the secondary coil 17 drops and the circuit breaking means 21 is turned on.

Thereby a current can be conducted from the accumulator means 15 to a second voltage regulator 22, which is connected to the lighting means 15. As indicated above, the lighting means 15 may comprise a plurality of light emit- ting diodes 23. In the embodiment shown seven groups connected in series are included, each group comprising four light emitting diodes connected in parallel. Thus, the lamp is switched on automatically in connection with being removed from the charging device.

In a preferred embodiment the lamp is entirely enclosed in a water- proof housing. By the means of an electric switch 24 arranged within the housing the lamp may be switched off. Suitably the electric switch is de- signed to be location or motion sensitive. Thereby switching off, and possibly also switching on, may be obtained by turning the entire lamp upside down.

Normally the lamps are switched off when positioned on the charging device. However, they can be switched on in this position by turning off or disconnecting the charging device 19.