EP0040339B1

EP0040339B1 - A centrally controlled lighting installation having a plurality of individually-switchable individual light points, central switch elements and individual light switches therefor

Info

Publication number: EP0040339B1
Application number: EP81103295A
Authority: EP
Inventors: Dieter Christiansen; Bernd Dr. Redies
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-17
Filing date: 1981-05-01
Publication date: 1985-08-07
Also published as: EP0040339A1; CA1197548A; DK216781A

Description

Lighting in comparatively large buildings, which involves a plurality of individual light points, is controlled automatically in many cases today by the artificial lighting being switched on or off, for example, when night falls or at sunrise. This is particularly appropriate in times of energy shortages, because the employee using the artificial light source does not often think in particular of switching off the lights and so the light source remains on, even when there is sufficient daylight in the place of work, or the light source cannot be individually switched off upon leaving the place of work before switching off by automatic operation. In offices, in which the energy requirement of the lighting may make up approximately 30% of the total energy requirement for the building, this may result in considerable and undesired costs.
The central automatic control of the lighting is effected, for example, by switch clocks set at specific times. As a result of the switching off operation, the circuit is permanently broken. However, the use of such switching systems has the disadvantage that weather conditions and changes in the intensity of daylight caused by the weather are not taken into account by the systems, so that when there is a dense covering of cloud after sunrise the lighting is switched off too early or when dense cloud is building up the artificial lighting is not turned on or it is turned on too late early in the evening. Switching systems of this type also only allow a central switching on or off of the complete installation.
There are also so-called "dimness switches", by which the artificial lighting is switched on or off depending on the actual intensity of daylight in a suitable manner by a current pulse released upon a specific light intensity. However, these systems also have the disadvantage that a control corresponding to the actual requirement of light in all parts of the building is impossible. The requirement for artificial lighting may vary quite considerably in the individual parts of the building, for example, depending on the aspect or on the distance from neighbouring houses and the height thereof or on the amount of trees in front of some of the windows of the building. This problem could, it is true, be alleviated by dividing the total lighting system into individual groups having a similar average light requirement and by switching the lighting on and off in each such section by a switch element controlled by natural light. However, the light requirement which varies considerably from person to person at the workplace cannot be considered either, so that people's health may also suffer to a considerable extent due to inadequate lighting, even with such a current-energy-saving central control of the lighting in buildings. In this case as well, all of the lighting plant (or sections thereof) may either be switched on or switched off, so that individual switching of the individual light point is again impossible. However, the arrangement of such control elements at each individual workplace in such buildings has been too expensive until the present time.
Furthermore there is known from FR-PS 22 62 896 a centrally controlled lighting installation giving satisfactory central control and the possibility of individual actuation of the individual light source or individual groups of light sources independent from the central control. This however only is possible with a control circuit in addition to the light circuit necessitating substitution of the present two-wire cabling by a four-wire cabling or, in newly erected buildings; the installation of such a four-wire cabling from the beginning which causes substantial additional costs.
Still furthermore known from the German prospectus "ELTAKO 3/80" is a magnetic switch of type ES 20.2 - 220V operated by current impulse. However, this switch is operated such that the current impulse either causes permanent closure or opening of the switch. A central switch-off of the total installation is possible by an interruption of the power supply for a period longer than a preset short period (about 0.2 s).
The object of this invention is to provide a lighting system having a plurality of individual light points which may be centrally controlled and in which each individual light point (or small groups of individual light points, such as the light points of an entire room) is simultaneously and individually switchable, so that even after general switching off of the lighting installation by the central control, individual light points (or groups of light points) may be switched on again or they may be switched off independently of the complete installation before the general switching off by the central automatic control. It is particularly the object of the invention to provide such a lighting system which is operable with the already generally installed and therefore generally available two-wire cabling, so that additional cabling and supplementary devices are not necessary.
Lighting circuit installation according to the invention centrally controlled by an impulse switch having a break contact, said lighting circuit having two terminals; an electric circuit between said two terminals; an individual light switch in said electric circuit, by which a light source or a group of light sources may be switched on and off independently of said impulse switch and which comprises a magnetic switch containing a magnet coil and a normally-open switch contact, said contact carrying the lighting current in working condition, and which contains, in addition thereto, means to open the electric circuit even with the magnetic switch being closed or to close the electric circuit even with the magnetic switch being open; a light source or a group of light sources being connected with the one of said two terminals and the individual light switch and the break contact of the impulse switch also being arranged in said electric circuit, is characterised in that the magnet coil of the magnetic switch is connected in series with its contact and carries the lighting current in working condition, and that the individual light switch is formed as a two-pole switch and comprises in addition to the magnetic switch as said means to open and close the electric circuit either:

a) means to open and close said contact of the magnetic switch mechanically from outside the individual light switch or
b) means to close said contact of the magnetic switch mechanically from outside the individual light switch and an additional switch connected in series with the contact of the magnetic switch operated by its magnet coil, said additional switch having a normally-closed contact which can be opened to break the circuit including the magnet coil or
c) two additional switches, one of said two additional switches having a normally closed contact (21) connected in series with the magnet coil and being openable to break the circuit including the magnet coil while the contact of the other of said two additional switches is normally open and is connected parallel to the contact operated by the magnet coil such that when closed it closes the circuit including the magnet coil even when the contact operated by the magnet coil is open.

The preferred embodiment of the lighting circuit installation according to the invention is characterised in that the magnetic switch is designed in the form of a double magnet having a common magnet core and two magnet coils connected in parallel, in each case with a switch con-. tact operated by the respective magnetic switch and connected in series to each magnet coil, whereby one magnet coil is designed for low magnet power and it closes its contact and keeps it closed when energised, while the other coil and optionally also the contact lever is designed such that its contact only closes the contact and may keep it closed when there is a current intensity which corresponds to at least approximately three times the minimum current intensity at which the magnetic switch with the magnet coil for low magnet power closes the switch contact associated therewith and keeps it closed.
Within the context of the present invention, the term "magnetic switch" is understood to mean a switch element having a switch contact and an electromagnet connected in series, which switch contact is closed and is kept closed when current flows through the electromagnet, e.g. by a lever arm which is then attracted by the electromagnet, and which is opened and is kept open when the current no longer flows through the electromagnet, e.g. by a spring acting on the switch contact or on the lever arm connected therewith or by a suitable three-dimensional arrangement or even by its inherent weight.
The lighting installation according to the invention is schematically illustrated and explained in the following drawings and circuit diagrams. Fig. 1 shows the lighting installation with the various embodiments of the individual light switches and a simple embodiment of the break contact (2) of the system. Fig. 2 shows the same installation with a detailed control system for said break contact (2). Fig. 3 shows another embodiment of the light switches in the electric circuit of the lighting circuit installation according to the invention. Fig. 4 shows the diagram of the control system for the break contact (2) separately as it is shown in Fig. 2. Fig. 5 shows a top view of such a control element.
The lighting installation illustrated in Fig. 1 with the power source (1) and the switch element (2) positioned centrally in the circuit has four individual light points, wherein individual switches 4, 6 and 8 provided with magnetic switches are associated with each of the individual light points 3 and 7 or with the group 5 of light points to be connected together, in the different embodiments of the lighting installation according to the invention. The individual switch 4 corresponds to embodiment a), the individual switch 6 corresponds to embodiment b) and the individual switch 8 corresponds to embodiment c).
The central switch element 2 has a normal switch position and a temporary adjustable, variable switch position, whereby the switch contact is closed in its normal switch position, e.g. by a suitable spring provided in the switch element, and thereby the circuit of the lighting installation according to the invention is also kept closed, whereas as a result of operating the switch element, e.g. by pressure'against the force of the spring, the switch contact and thereby the circuit of the lighting plant according to the invention may be broken for a short time.
In the embodiment a) of the individual light switch 4 associated with the individual light point 3, the magnetic switch is not only designed such that it may be operated by the lever arm 11, which is attracted by the electromagnet 9, is positioned rotatably at one of its ends and simultaneously causes the contact closure of the switch contact 10 of the magnetic switch, but it is also designed so that it may be opened and closed mechanically from outside via the operating lever 12 which is rotatably secured on its other free end.
If, in embodiment a) of the lighting installation according to the invention, the current is interrupted for a short time by operating the central switch 2, the electromagnet 9, due to the inherent weight of the lever arm 11 positioned thereunder, releases this arm 11, so that the switch contact 10 is opened and is kept open even when the central switch 2 returns to its closed normal switch position. If artificial light is required at the individual light point against the command of the central switching point 2, the switch contact 10 is closed by pressing in the operating lever 12 of this embodiment of the individual switch and it is kept closed due to the resulting flow of current through the electromagnet 9. However, if switching off of this individual light point is required or a switching off of the light point which has been subsequently switched on again as described is required before the central switching off of the entire lighting installation, effected by operating the circuit element 2, the switch contact 10 is opened by pushing the operating lever 12 up, applying an adequate pressure against the attractive force of the electromagnet 9, so that the electromagnet loses its attractive force and the switch contact 10 is opened.
In the embodiment b) of the lighting installation according to the invention, the magnetic switch is only designed so that it may also be closed mechanically from outside. On the frame of the individual switch 6 associated with the individual light point 5, the switch contact 13 of the magnetic switch may not only be operated by the electromagnet 14 and its lever arm which may be attracted by the electromagnet 14, but the switch contact 13 may also be closed using the lever arm 15 which may be operated from outside the individual switch 6 by pressing in this lever arm 15. The switch element 16, 17 having a normal switch position and a temporary adjustable, variable switch position is also provided in the individual switch, is connected in series to the magnetic switch and which, like the central switch element 2 keepts its switch contact 17 and thereby the circuit closed in its normal switch position and when it is operated by pressing in the "Off" part of the operating switch, the switch contact 17 is broken for a short time via its operating lever 16 and thus the circuit is also broken for a short time.
If, as in the previously described case, the central switch 2 is opened for a short time, the current flow in the electromagnet 14 and thus the resulting attraction is terminated and the electromagnet 14, due to, for example, a spring acting on the lever arm of the magnetic switch, releases the attracted lever arm and the switch contact 13 of the magnetic switch is opened and is kept open as a result of this action. If the individual light point is to be switched on again against the central control command of the switch element 2, the switch contact 13 of the magnetic switch and thus the complete circuit is closed by pressing in this lever arm 15 and, due to the then restored attraction of the electromagnet 14, the switch contact 13 is kept closed. If the individual light point is then to be later switched off again, the circuit is broken for a short time by operating the switch element 16, 17 provided in the individual switch 6 and thus associated with the magnetic switch, so that the electromagnet 14 releases the lever arm of the magnetic switch and it re-opens its switch contact 13 and keeps it open. Thus, in the individual switch of the embodiment b) of the lighting installation according to the invention, the switch contact 13 of the magnetic switch takes over the switching on operation, apart from keeping its contact closed, whereas the switching off operation is taken over by the switch element 16, 17 associated therewith. Since, as is known, due to the closing or opening operation of switch contacts and the sparking caused by these operations, power peaks may occur, the magnet coil in embodiment b) may optionally be provided with a lower capacity as compared to embodiment a).
The embodiment c) provides an even lower load for the magnetic switch, in which embodiment the switch contact 18 of the magnetic switch together with its magnet 19 only takes over the task of keeping the circuit closed. In addition to the switch element 20, 21 of the embodiment b) connected in series to the magnetic switch, another switch element 22, 23 having a normal switch position and a temporary adjustable, variable switch position is provided which is connected parallel to the switch contact 18 of the magnetic switch and is connected in series to the magnet 19 of the magnetic switch and it keeps its switch contact 23 open in its normal switch position and its switch contact is closed for a short time when it is operated, so that the magnetic switch is designed to be operated from outside without any additional mechanical possibility. As a result of pressing in the operating lever 20 associated with the switch contact 21, the circuit is broken for a short time, whereas upon pressing the operating press lever 22 associated with the switch contact 23, the circuit is even closed when the switch contact 18 of the magnetic switch is open.
If, as in the previously mentioned examples, the central switch 2 is operated and a result of this, the circuit is broken for a short time, the switch contact 18 of the magnetic switch is opened, for example, due to a spring provided in the magnetic switch and holding its lever arm. If the individual light point is to be switched on again against the command of the central switching point 2, the switch contact 23 is closed for a short time by actuating the operating lever 22, designed in this case as a rocker switch, and the switch contact 18 of the magnetic switch is closed and is kept closed, due the current flow through the electromagnet of the magnetic switch. If the individual light point is then to be switched off again independently of the central control, the switch contact 21 and thus the circuit for the individual light switch 7 is broken for a short time by actuating the operating lever 20 and thus, the switch contact 18 of the magnetic switch associated therewith is also reopened.
Limited by the two-wire design and thus by the load switching of the magnet coil of the magnetic switch and the considerable load variations in the circuit of such lighting installations, the magnet of the magnetic switch may be charged with different loads such that by adjusting the design of the coil according to the load peak, the magnet of the magnetic switch is not yet energised enough in the lower load range to reliably close the switch contact of the magnetic switch and to also keep it closed. However, if the coil of the magnetic switch is designed such that the switch contact of the magnetic switch is closed reliably even in the lower load range and is kept closed with an adequate strength, there is a danger of considerable overheating of the magnet and thus a danger of fire in the building having such lighting installations where there is a load in the range of the peaks or even in the middle range of the load variations. In addition thereto, magnetic switches of this type have to be so large that it is no longer possible to house the individual switches produced therewith in conventional sized counter- sinkable wall boxes. However, it is a particular object of an embodiment of the present invention to design the individual light points or groups of individual light points to be able to be switched on and off while using available two-wire lighting installations with conventionally-sized connection boxes and without additional devices, i.e. exchanging the old switches for the new individual switches in lighting installations controlled centrally by a current pulse.
Another embodiment of the lighting installation according to the invention and of its individual light switches relates to the magnetic switches 9, 10, 11, 12 or 13, 14, 15, or 18, 19 of the individual switches. It is schematically illustrated in Figure 3, for the magnetic switches 13, 14, 15 or 18, 19 of the individual switches. This applies accordingly to the magnetic switch 9, 10, 11, 12 of embodiment a).
The embodiment, which is improved with respect to heat control and is therefore particularly preferred, is characterised in that the magnetic switch is designed in the form of a double magnet having a common magnet core and two connected magnet coils 9a and 9b connected in parallel or 14a and 14b or 19a and 19b having respectively a switch contact 11a and 11 b or 13a and 13b or 18a and 18b operated by the respective magnetic switch and connected in series to each magnet coil. One magnetic coil is designed for low magnet power and it closes its contact when energised and keeps it closed, whereas the other coil and optionally also the contact lever of the switch contact associated with this coil is designed such that its switch contact only closes the contact and keeps it closed at a current intensity which corresponds to at least approximately three times, preferably four times, the minimum current intensity at which the magnetic switch with the magnet coil for low magnet power closes the switch contact associated therewith and keeps it closed.
According to a preferred embodiment, the two magnet coils of the double magnet connected in parallel to each other are wound one upon the other over a common magnet core.
It is most particularly preferred for the common magnet core of the double magnet to be formed from sheets mounted in parallel.
In these preferred embodiments with double magnet, the variation range of the magnet power due to the load switching of the magnet coil is thus subdivided so that it is not necessary to construe the magnet coil to meet the highest magnet power demand with in this variation range in order to avoid the generation of an excessive amount of heat. The exact division of the total power range is appropriately effected in that the magnet coil designed for low magnet power covers approximately one third of the total variation range and approximately two thirds of the range is controlled by the magnet coil designed for greater magnet power. In this operation, the best division is to be established empirically for the respective design of the double magnet and switch contacts.
Instead of the magnetic switch, other switch elements which may be operated by a temporary current pulse, such as relays controlled by a transistor, may also be used, in particular in the embodiment c) of the lighting installation according to the invention, as long as the relay is opened by this current pulse retransmitted via the mains of the lighting installation and may be opened and closed according to the individual embodiments from outside, and also separately for each individual light point, whether it is fully mechanical, according to embodiment a), partly mechanical according to embodiment b) or fully nonmechanical by suitable pulse transmitters associated with the individual light points according to embodiment c). However, the switch element 2 must then also be replaced by a suitable central pulse transmitter. The embodiment illustrated, in which the control pulse is provided by a temporary interruption in the current, allows, however, a particularly simple design and is therefore preferable.
The central switch element 2 may be operated manually or using suitable control devices. According to a particularly preferred embodiment, the central switch element 2 constitutes a switch element which may be operated by the energising of a magnet coil and this switch element is controlled both by a conventional switch clock having at least two adjustable switch positions for actuating the switch of the switch clock as well as by a dimness switch connected in parallel thereto and optionally adjustable with respect to the light sensitivity. A control element of this type is schematically illustrated in Figure 2 of the drawings as well as being illustrated as a separable part of the lighting installation in Figures 4 and 5. This control element has a conventional switch clock 24 with a conventional seven day/24 hour program and has at least two adjustable switch settings for actuating the switch of the switch clock 24 designed as a brush contact, a dimness switch 25 which is optionally adjustable with respect to the light sensitivity with a switch designed as a brush contact and having a separate light sensor 26 which may be connected via the terminal 32, a changeover switch 27 for connecting a first terminal of the switch contact with selectively either the one or other second terminal of the switch contact or with both terminals, a switch 2 which may be operated by exciting a magnet coil 28 and having a normal switch position while closing its switch contact and a variable switch position which may be adjusted for a short time by operating the switch, while opening the switch contact. The main voltage of the power source 1 is transformed by the transformer 29 to the control voltage of the control device for the central switch element 2.
According to a preferred embodiment, the control device also has a switch 30 on the frame whose switch contact is connected in parallel to the switches of the switch clock 24 and the dimness switch 25 and whose switch lever may be actuated mechanically or electromagnetically or the like, for example by a ripple central signal provided by an external signal transmitter 31.
Thus, the lighting installation according to the invention may be set for light or time-control or for both together by the change-over switch 27, so that the control may be effected both by the intensity of daylight as well as by the switch dock, so that, for example, in summer with a specific daylight intensity, the first switching off is effected centrally and a second control switching off may be carried out at a later time. Therefore, an extremely versatile control of the lighting installation according to the invention, being dependent on numerous conditions is possible with this control device.

Claims

1. Lighting circuit installation centrally controlled by an impulse switch having a break contact (2), said lighting circuit having two terminals; an electric circuit between said two terminals; an individual light switch (4; 6; 8) in said electric circuit, by which a light source (3; 7) or a group of light sources (5) may be switched on and off independently of said impulse switch (2) and which comprises a magnetic switch containing a magnet coil (9; 9a; 14; 14a; 19; 19a) and a normally-open switch contact (10; 13; 18), said contact carrying the lighting current in working condition, and which contains, in addition thereto, means (12; 15; 16; 20; 22) to open the electric circuit even with the magnetic switch being closed or to close the electric circuit even with the magnetic switch being open; a light source (3; 7) or a group of light sources (5) being connected with the one of said two terminals and the individual light switch (4; 6; 8); and the break contact (2) of the impulse switch also being arranged in said electric circuit, characterised in thatthe magnet coil (9; 9a; 14; 14a; 19; 19a) of the magnetic switch is connected in series with its contact (10; 13; 13a; 18; 18a) and carries the lighting current in working condition, and that the individual light switch (4; 6; 8) is formed as a two-pole switch and comprises in addition to the magnetic switch as said means to open and close the electric circuit either:

a) means (12) to open and close said contact (10) of the magnetic switch mechanically from outside the individual light switch (4) or

b) means (15) to close said contact (13; 13a) of the magnetic switch mechanically from outside the individual light switch (6) and an additional switch (16; 17) connected in series with the contact (13; 13a) of the magnetic switch operated by its magnet coil (14; 14a), said additional switch (16; 17) having a normally-closed contact (17) which can be opened to break the circuit including the magnet coil or

c) two additional switches (20; 21; 22; 23), one of said two additional switches having a normally closed contact (21) connected in series with the magnet coil (19; 19a) and being openable to break the circuit including the magnet coil, while the contact (23) of the other of said two additional switches is normally open and is connected parallel to the contact (18; 18a) operated by the magnet coil (19; 19a) such that when closed it closes the circuit including the magnet coil even when the contact (19; 19a) operated by the magnet coil (19; 19a) is open.

2. A centrally-controlled lighting circuit installation according to claim 1, characterised in that the magnetic switch is designed in the form of a double magnet having a common magnet core and two magnet coils (9a; 9b; 14a; 14b; 19a; 19b), connected in parallel, in each case with a switch contact (11a; 11b; 13a; 13b; 18a; 18b) operated by the respective magnetic switch and connected in series to each magnet coil, whereby one magnet coil (9a; 14a; 19a) is designed for low magnet power and it closes its contact (11a; 13a; 18a) and keeps it closed when energised, while the other coil (11b; 14b; 19b) and optionally also the contact lever is designed such that its contact only closes the contact (11 b; 13b; 18b) and may keep it closed when there is a current intensity which corresponds to at least approximately three times the minimum current intensity at which the magnetic switch with the magnet coil for low magnet power closes the switch contact associated therewith and keeps it closed.

3. A centrally-controlled lighting circuit installation according to claim 2, characterised in that the two magnet coils (9a; 9b; 14a; 14b; 19a; 19b) of the double magnet connected in parallel to each other are wound one upon the other over a common magnet core.

4. A centrally-controlled lighting circuit installation according to claims 2 or 3, characterised in that the common magnet core of the double magnet is formed from sheets packed in parallel.

5. A centrally-controlled lighting circuit installation according to any of claims 1 to 4, characterised in that the switch of the central switch element (2) is a switch which may be operated by the energising of a magnet coil (28), and it may be energised by a conventional switch clock (24) having at least two adjustable switch positions for actuating the switch of the switch clock (24) or by a dimness switch (25) having a light sensor (26), the dimness switch being optionally adjustable with respect to the light sensitivity, or it may be energised by another signal transmitter (31) or by several of these signal transmitters combined.

6. A control element of the lighting circuit installation according to claim 5, characterised in that the following elements are positioned on a frame having a suitable covering: the conventional switch clock (24); the dimness switch (25) which may be connected via a terminal (32) to the light sensor (26); a change-over switch (27) for connecting a first terminal of the switch contact with selectively either one or other second terminal of the switch contact or jointly with both terminals; the switch (2; 28) of the central switch element (2) having a normal position, while closing its switch contact (2), and a variable switch position, which may be adjusted for a short time by operating said switch, while opening its switch contact; and three external terminals whereby the first terminal is connected to one terminal of the switch contact (2) of said switch as well as to the switch contact of the switch clock (24), the second external terminal is connected to the other terminal of the switch contact (2) of said switch, and the third external terminal is connected to one terminal of the magnet coil (28), while the other terminal of the magnet coil (28) is connected to the other terminals of the switch contacts of the dimness switch (25) via the change-over switch (27).

7. A control element according to claim 6, characterised in that a switch (30) is also provided whose contact terminals are connected to the first external terminal and the magnet coil (28), connected parallel to the contacts of the dimness switch (25) and the conventional switch clock (24), and whose switch lever may be actuated mechanically or electromagnetically or the like by an external signal transmitter (31) which may be connected via an additional fourth external terminal.

8. An individual light switch (4), forming a two-pole switch, of the centrally-controlled lighting installation according to one or more of claims 1 to 7, characterised in that the switch contact (10) of the magnetic switch is designed such that it may be closed and kept closed by its electromagnet when current flows through its magnet coil (9) and it may also be closed or opened mechanically from outside the individual light switch (4).

9. An individual light switch (4) according to claim 8, characterised in that an at least partly magnetizable lever arm (11) is rotatably secured at one end on a suitable frame of a conventional size for light switches such that in the position which corresponds to the position after installation in the place of use the lever arm (11) is rotatable about a horizontal axis, is designed as a switch contact lever electroconducting in one part (10), and is rotatably connected at its other end with a lever (12), which is secured rotatably in one point of the individual light switch (4) positioned towards the top of the place of use and is secured so that it may be pivoted upwards and downwards and which in the lower position presses the lever arm (11) with its electroconducting part, forming the switch contact (10), against two connection terminals secured to the frame while closing this switch contact (10) and presses the magnetizable part of the lever arm (11) against the magnet core of the electromagnet with its coil (9) so that the electromagnet holds the lever arm (11) in this position during the current flow, but when there is an interruption in the current flow through the magnet coil (9), it turns away due to its inherent weight or due to a spring of the electromagnet holding the lever arm (11), while keeping the switch contact (10) open.

10. An individual light switch (6), forming a two-pole switch, of the centrally-controlled lighting installation according to one or more of claims 1 to 7, characterised in that the contact (17) of a switch element (16; 17), forming said additional switch, which may be operated independently from the switch contact (13) of the magnetic switch and which has a normal switch position and a temporary adjustable, variable switch position, is connected within the internal circuit between the two poles.

11. An individual light switch (6) according to claim 10, characterised in that said additional switch is designed as a magnetic switch whose magnet coil and switch contact, forming the switch element (17), are connected in series.

12. An individual light switch (6) according to claim 10 or 11, characterised in that the switch contact-(13) of the magnetic switch is firmly connected to its lever arm (15) and that a spring element of the magnetic switch causing the return to its normal switch position is designed such that on one hand, during an interruption in the current flow, the switch contact (13) of the magnetic switch is opened and is kept open, and on the other hand, after closing of the switch contact (13) of the magnetic switch during current flows through its magnet coil (14), the resulting magnetic force keeps the switch contact (13) of the magnetic switch closed.

13. An individual light switch (6) accoring to one or more of claims 10, 11 and 12, characterised in that the operating parts of the switch elements (16; 17) and (13; 15) are designed and combined in the form of a known rocker switch having a central neutral switch position.

14. An individual light switch (8), forming a two-pole switch of the centrally-controlled lighting installation, according to one or more of claims 1 to 7, characterised in that a switch element (18; 19), forming said magnetic switch, which may be operated by a temporary current pulse applied to the internal electrical circuit between the two poles; and two switch elements (20; 21) and (22; 23), forming said two additional switches respectively, which may be operated independently of each other having a normal switch position and a temporary adjustable, variable switch position, whereby the switch contact (21) of one switch element is connected into the internal electrical circuit between the two poles and closes this internal electrical circuit in its normal switch position, whereas the switch contact (23) of the other switch element is connected in parallel to the switch contact (18) such that it even closes for a short time the internal electrical circuit between the two poles in its temporary adjustable, variable switch position when the electrical connection is opened by the switch contact (18).

15. An individual light switch (8) according to claim 14, characterised in that the switch contact (18) is designed to be actuated by a magnet coil (19) and the switch contact (18) actuated thereby are connected in series to each other in the internal electrical circuit between the two poles so that the switch contact (18) is closed when current flows through this internal electrical circuit, and it is kept closed as long as current flows through it and it is opened when there is no current flowing through the magnet coil (19).

16. An individual light switch (8) according to claim 14 or 15, characterised in that the two switch elements (20; 21; 22; 23) are designed and combined in the form of a known rocker switch having a central neutral switch position, whereby in the central neutral position, the one switch element keeps its switch contact (21) and thereby the electrical connection closed and opens it for a short time upon actuation, whereas the other switch element keeps its switch contact (23) open and closes it for a short time upon actuation.