GB2388260A

GB2388260A - Emergency lighting

Info

Publication number: GB2388260A
Application number: GB0210205A
Authority: GB
Inventors: Angus Stone
Original assignee: Cooper Lighting & Security Ltd; Cooper Lighting and Security Ltd
Current assignee: Cooper Lighting & Security Ltd; Eaton Electrical Systems Ltd
Priority date: 2002-05-03
Filing date: 2002-05-03
Publication date: 2003-11-05
Anticipated expiration: 2022-05-03
Also published as: GB2388260B; GB0210205D0

Abstract

The system shown diagrammatically in Figures 2a and 2b uses capacitive coupling between two electrodes 10a and 10b and a fluorescent lamp tube 12 in order to provide emergency ignition of the fluorescent lamp 12 when an emergency inverter is triggered to provide an emergency power supply. The emergency lighting system does not connect via cathodes 14 of the fluorescent lamp 12, in order to prevent damage thereof.

Description

Emergency Lighting This invention relates to an emergency lighting system

and to a method of illuminating an emergency light.

Existing emergency lighting circuits typically operate by connecting an emergency inverter to a fluorescent lamp and operating at low brightness with minimum power, in order to aim for maximum efficiency. As a result, no power is lo used for cathode heating in the fluorescent lamp. Using this method, the cathodes will often run at lower than designed temperatures and damage is sustained as a result.

Such damage is disadvantageous to the correct working of 15 the fluorescent lamps.

In addition, there have been developments in lamp technologies aimed at reducing environmentally harmful chemicals used in lamps, such as mercury. Developments 20 have also been made to reduce the cost of the lamps. As a result of these changes, the lamps have become less robust and more prone to damage when used on emergency circuits.

It is an object of the present invention to address the 25 above mentioned disadvantages.

According to a first aspect of the invention a lighting system comprises: at least one power supply; 30 at least one fluorescent lamp; primary ignition means for the lamp; and secondary ignition means for the lamp.

( 2 The fluorescent lamp is preferably tube shaped.

The primary ignition means preferably comprise standard ignition means for a fluorescent lamp, which means 5 preferably comprise first and second electrodes within the lamp, which may be effectively at opposite ends thereof.

The secondary ignition means are preferably capacitive ignition means, operable to ignite the lamp by means of a 10 capacitive effect between the lamp and the secondary ignition means.

The secondary ignition means preferably comprise at least two electrodes. The electrodes are preferably secured to 15 an exterior of the lamp. The electrodes are preferably located at substantially opposite ends of the lamp, but preferably far enough away from electrodes of the primary ignition means so as to minimise coupling from the secondary to the primary ignition means.

The electrodes may partially surround the lamp, and may have a partial ring shape.

The electrodes may be shaped so as to form a minimum 25 distance between the electrode material and an envelope of the lamp and may be of a sufficient size so as to maintain a minimum capacitance as required by the design of the system. The actual shape and design of the electrodes is preferably dependent on the design of the lamp.

The system may have first and second power supplies. The first power supply may be a standard/mains power supply.

The second power supply may be an emergency power supply.

The second power supply may operate at a frequency of greater than about lMHz, so as to minimise the effect of the coupling capacitance and hence minimise the second 5 power supply output voltage. The frequency is preferably greater than about 2MHz, preferably less than about 3MHz, most preferably in the range 2.4-2.8MHz, so as to be most favourable with respect to current EMC legislation in Europe. The second power supply preferably operates at a power of less than about 15W, preferably less than about lOW, most preferably less than about 5W. The second power supply is sized dependent on the light output requirements. A power 15 level of 5W has been found to give good emergency illumination with current designs of luminaire and typical office ceiling heights. Higher light outputs may be required in applications where the emergency luminaire is mounted at greater mounting heights.

The electrodes may be located approximately 30mm to 60mm from opposite ends of the lamp. The electrodes may have a separation of at least about 40cm.

gs The invention extends to a lighting system having at least one power supply, primary ignition means for a fluorescent lamp and secondary ignition means for a fluorescent lamp.

According to a second aspect of the invention an emergency 30 lighting system comprises: a power supply; and capacitive ignition means for at least one lamp.

The emergency lighting system is preferably adapted to be retrofitted to an existing lighting system having at least one primary power supply and at least one fluorescent lamp. According to a third aspect of the invention a method of lighting an emergency lighting system comprises: capacitively coupling secondary ignition means to a lighting system comprising at least one power supply, at lo least one fluorescent lamp and primary ignition means.

The capacitive coupling may be achieved by external electrodes. 15 The capacitive coupling may be performed at a frequency of greater than about lMHz, preferably greater than about 2MHz, preferably between about 2.4 and 2.8MHz.

The capacitive coupling may be performed at a power of 20 less than about 15W, preferably less than lOW, preferably less than 5W.

According to a fourth aspect of the invention a lighting system comprises: 25 a first power supply; a second power supply; and at least one fluorescent lamp; wherein the fluorescent lamp is operable to be illuminated by capacitive ignition means of the lighting 30 system.

The lighting system is preferably an emergency lighting system.

Preferably, the first power supply is a mains power supply. 5 Preferably, the second power supply is an emergency power supply, preferably a battery.

Preferably, the first and second power supplies both supply the capacitive ignition means.

Preferably, the fluorescent lamp is of a standard type, having internal cathodes for ignition.

Preferably, the capacitive ignition means comprise at 5 least two electrodes, preferably adapted to be coupled with the fluorescent lamp.

The invention extends to a lighting system having first and second power supplies and capacitive ignition means 20 operable to illuminate a fluorescent lamp.

All of the features described herein may be combined with any of the above aspects, in any combination.

25 Specific embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of drive 30 electronics for an emergency lighting circuit;

Figures 2a and 2b show schematic side and end views respectively of a first embodiment of a secondary drive system for an emergency lighting system; and s Figures 3a and 3b show similar views to Figures 2a and 2b for a second embodiment.

The system shown diagrammatically in Figures 2a and 2b uses capacitive coupling between two electrodes lea and lo lob and a fluorescent lamp tube 12 in order to provide emergency ignition of the fluorescent lamp 12 when an emergency inverter is triggered to provide an emergency power supply. The emergency lighting system does not connect via cathodes 14 of the fluorescent lamp 12, in 15 order to prevent damage thereof.

In more detail, the electrodes in Figure 2a have a width of approximately 40mm and, as shown in Figure 2b extend approximately half way around the tube 12. The two JO electrodes lea and lob have a separation of approximately 0.5m and they are approximately 50mm from respective ends of the tube 12. The electrodes lOa and lOb are connected to an emergency inverter which provides a power supply, described below. The emergency inverter, shown by the 25 parts outside box A in Figure 1, is characterized by the power requirements (light output) of the emergency application, it is adapted to specific lamp types by the design of the electrodes lea, lOb.

30 The electrodes may be secured in position with adhesive or clips. The clip may be formed from the shape of the electrode or via a bracket feature, which either attaches to the lamp 12 or a luminaire (not shown) so as to hold

the conductive part of the electrode against an envelope (glass portion) of the lamp 12.

Electrical wires 16a and 16b extend to the emergency 5 inverter.

The electrodes lea and lob are provided with power by the schematic circuit shown in Figure 1. In Figure 1 the box marked A represents the elements of the system shown in lo Figures 2a and 3a.

The drive circuitry in Figure 1 comprises a signal generator 18, designed to operate at the system frequency, connected to an RF amplifier 20. The RF amplifier 20 is 15 used to provide power. A transformer 22 is provided for impedance matching at the required drive voltages. The transformer 22 is centre tapped at 24 for impedance matching at required voltages. Centre tapping also ensures even tube illumination by avoiding asymmetrical 20 ground plane issues. A capacitor 26 is also provided for impedance matching. The emergency inverter also incorporates a battery and battery charger fed from the mains and designed to operate the circuitry of Figure 1 from the battery in the event of mains failure. The 25 signal generator 18 and RF amplifier are typically implemented as a single unit, particularly in commercial implementations. The drive voltages that are required are approximately 30 340V when running and approximately 5-10% higher than this to strike the tube, depending upon the tube quality and type.

With power supply to the electrodes lea and lob provided by the drive circuit shown in Figure 1, capacitive coupling between the electrodes and the tube 12 results in low level illumination of the tube. This bypasses the 5 cathodes 14 which are the usual means for illuminating the tube 12, as is well known.

Typically, the cathodes 14 are heated, which requires a large amount of energy. This creates free charge carriers lo around the cathodes which allows an arc to be struck in the lamp gas from a reasonably low voltage, as supplied by the normal control circuitry. By contrast, using a higher frequency, the electrodes lOa and lob give rise to an electric field which passes through the glass of the lamp

IS 12 to the gas in the lamp 12, thereby causing the gas to fluoresce and emit light. A higher voltage is required to overcome the effect of the capacitor drop and the fact that the electrodes lea, b are not heated.

20 Figures 3a and 3b show a second embodiment of electrode lea and lob which are in the shape of a ring surrounding the tube 12. The other parts of the system as described in relation to Figures 2a and 2b are the same. The electrodes lea and 10 have a width of approximately 25mm, 25 but otherwise the sizes, locations, separations etc are the same as described in Figure 2a.

The following is a table giving figures for the operation of the tube 12 in normal conditions using the cathodes 14 30 (shown as "normal operation" in the table). The following values are given: frequency at which the tube 12 is driven, a light output reading in Lux, an electrical mean

input in Watts, a light output in Lumens, and an efficiency in Lumens/Watt.

When running on a prior art emergency battery at 50KHz

5 using the cathodes 14 at low power figures are given.

Also, figures for the arrangement shown in Figures 2a and 2b are shown, described as "cups" in the table.

Configuration Frequency Light Electrical Input Light Efficiency Reading (mean) Watts Output Lumens/Watt _ Lumens Normal operation 50Hz 133 0 18. O 768.4 42.7 Emergency Battery 50kHz lSO 2. S 86.7 35. 4 Cups Z. 6MHz 150 3.6 Be.7 24.1 As can be seen, the normal operation of the tube 12 requires a greater electrical input and is the most efficient means of operating the tube 12. The emergency 5 battery and cup configuration shown in Figures 2a and 2b compare well with each other, with the significant advantage of the cups arrangement shown in Figures 2a and 2b providing greater longevity of the tube 12, because the cathodes 14 are not used in this arrangement.

The cups of Figure 2 and the rings of Figure 3 both performed similarly.

Having conducted the tests, it was determined that the 25 optimal configuration, when considering ease of assembly and disassembly, would be the cup arrangement shown in Figures 2a and 2b in which the electrodes have a width of 40mm. The electrodes lea and lob should be placed a small

distance from the ends of the tubes, to avoid edge-effects and sputtering of the internal electrodes (cathodes) 14.

Due to the operation of the system it is possible for a 5 single power supply to operate a wide range of different lamps. Some matching may be required for optimum performance. It is necessary to design electrodes to suit the various lamp types. For example the common types of linear fluorescent lamps are T5, TO and T12 with diameters lo 16mm, 25mm and 38mm respectively. The electrodes must be shaped to fit closely against the lamp walls and this can be achieved using a spring form or separate electrode styles. Single ended fluorescent lamps have been found to work better with one electrode close to the lamp end and 5 the other close to the lamp bridge. Each electrode operating both 'legs, of the lamp. Some experimentation is required to successfully operate each style of compact fluorescent lamp due to varying shape of the lamp envelopes used.

The electrodes and tube have been tested with the electrical wires 16a/b running approximately parallel to the tube 12 at a separation of approximately lOmm, as shown in Figure 2a. This provides a balanced loop 25 orientation and is an elegant way in which to reduce stray capacitance and stray fields near the tube by using the

tube symmetry. However, it is believed that this is not critical to emission output. Radiated emissions were tested with the tube both fitted inside and outside a 30 representative metal luminaire housing.

As far as the drive circuit was concerned, it was found that the area of contact between the electrode lOa/b and

the tube 12 is important in determining the level of coupling at the selected frequency, because capacitance is proportional to area. Also, operating at frequencies lower than lMHz requires a prohibitively high drive 5 voltage amplitude. The best electrical coupling through the glass walls of the tube 12 (with a thickness of 600 microns) occurs when using frequencies over lMHz. Thus, the consequences of this effect were considered in designing the system to meet radiated emissions lo specifications, thus the range 2.2-3.0 MHz was chosen.

As can be appreciated from the above, the configuration shown in Figures 2a and 2b provides an efficient low power system for an emergency inverter to illuminate a standard fluorescent tube 12, without damaging the cathodes 14 of the tube, which are used for normal illumination.

Thus, significant advantages in relation to longevity of the tube can be achieved with little or no reduction in 20 efficiency of low power operation. A number of configurations of the capacitive electrodes can be used, but the cup version shown in Figures 2a and 2b is preferred. 25 The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and

which are open to public inspection with this specification, and the contents of all such papers and

30 documents are incorporated herein by reference.

All of the features disclosed in this specification

(including any accompanying claims, abstract and

drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including

any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated lo otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the 15 foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any

accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any 20 method or process so disclosed.

Claims

CLAIMS:

I. A lighting system comprises: at least one power supply; 5 at least one fluorescent lamp; primary ignition means for the lamp; and secondary ignition means for the lamp.
2. A lighting system as claimed in claim 1, in which the lo primary ignition means comprises standard ignition means for a fluorescent lamp.
3. A lighting system as claimed in claim 2, in which the primary ignition means comprise first and second electrodes within the lamp.
4. A lighting system as claimed in any preceding claim, in which the secondary ignition means are capacitive ignition means, operable to ignite the lamp by means of a 20 capacitive effect between the lamp and secondary ignition means.
5. A lighting system as claimed in any preceding claim, in which the secondary ignition means comprises at least 25 two electrodes.
6. A lighting system as claimed in claim 5, in which the electrodes are secured to an exterior of the lamp.

30
7. A lighting system as claimed in either claim 5 or claim 6, in which the electrodes are located at substantially opposite ends of the lamp.
8. A lighting system as claimed in any one of claims 5 to 7, in which the electrodes partially surround the lamp.
9. A lighting system as claimed in any preceding claim, 5 which has first and second power supplies.
10. A lighting system as claimed in claim 9, in which the first power supply is a standard/mains power supply.

lo
11. A lighting system as claimed in either claim 9 or claim 10, in which the second power supply is an emergency power supply.
12. A lighting system as claimed in any one of claims 9 to 11, in which the second power supply operates at a frequency greater than about 2MHz.
13. A lighting system as claimed in any one of claims 9 to 12, in which the second power supply operates at a power 20 of less than about 5W.
14. A lighting system having at least one power supply, primary ignition means for a fluorescent lamp and secondary ignition means for a fluorescent lamp.
15. An emergency lighting system comprises: a power supply; and capacitive ignition means for at least one lamp.

30
16. An emergency lighting system as claimed in claim 15, which is adapted to be retro-fitted to an existing lighting system having at least one primary power supply and at least one fluorescent lamp.
17. A method of lighting an emergency lighting system comprises: capacitively coupling secondary ignition means to a 5 lighting system comprising at least one power supply, at least one fluorescent lamp and primary ignition means.
18. A method as claimed in claim 17, in which the capacitive coupling is achieved by external electrodes.
19. A method as claimed in either claim 17 or claim 18, in which the capacitive coupling is performed at a frequency of greater than about 2MHz.

15
20. A lighting system comprises: a first power supply; a second power supply; and at least one fluorescent lamp; wherein the fluorescent lamp is operable to be so illuminated by capacitive ignition means of the lighting system.
21. A lighting system as claimed in claim 20, which is an emergency lighting system.
22. A lighting system as claimed in either claim 20 or claim 21, in which the first power supply is a mains power supply. 30
23. A lighting system as claimed in any one of claims 20 to 22, in which the second power supply is an emergency power supply.
24. A lighting system as claimed in any one of claims 20 to 23, in which the fluorescent lamp is of a standard type, having internal cathodes for ignition.

5
25. A lighting system having first and second power supplies and capacitive ignition means operable to illuminate a fluorescent lamp.
26. A lighting system substantially as described herein lo with reference to the accompanying drawings.
27. A method of lighting an emergency lighting system substantially as described herein with reference to the accompanying drawings.