GB2239941A - Emergency indicator light - Google Patents

Abstract

An emergency indicator light for use particularly in indicating an escape route from a building in the event of a fire has an electroluminescent panel (1) mounted parallel to and behind a face plate (10) incorporating an indicator symbol such as an arrow. The panel (1) is powered by a battery-powered inventor circuit which is activated when the mains supply fails. The light is constructed for low-level wall mounting, for instance in an existing power outlet box, for improved visibility in a smoke-filled building. <IMAGE>

Description

EMERGENCY INDICATOR LIGHT The present invention relates to emergency lighting, particularly but not exclusively for use in buildings to aid escape from smoke-filled corridors and rooms.

Most hotels and public buildings have some form of emergency lighting to indicate a safe, illuminated escape route in the event of a failure of the mains electricity supply and hence of the normal lighting. The failure of the mains supply may be due to a failure of supply to the whole building or to the local sub-circuit or may be caused by the activation of a fire alarm system. In the event of such a failure due to fire, however, some areas of the building may become filled with smoke. In this case, the normal and emergency lighting may have little or no effect.

The object of the present invention is to provide an emergency light which is not affected by failures of the mains supply and can provide a clearly indicated escape route that is readily visible in smoke-filled corridors and rooms, and which is easy and convenient to install.

Accordingly, the present invention provides an emergency indicator light comprising a battery-powered electroluminescent light source and an activating circuit having an input for connection to a mains electricity supply for monitoring the latter and adapted to activate the light source under battery power in the event of a predetermined drop in the mains supply voltage.

In a preferred embodiment the light is intended to be wall-mounted in a room or corridor of a building at skirting board level so that the light source illuminates an arrow showing the way to the nearest exit.

The light preferably includes driving circuitry associated with an electroluminescent panel including a battery and monitoring means connected to the mains supply. The entire light may be of a suitable size to fit a standard 13A double back box so that the light can be installed easily in an existing building.

The electroluminescent light source is preferably covered by a partially opaque face plate which allows a predetermined symbol to be defined by the illumination of the lighttransmitting areas of the plate.

The driving circuit for the light source preferably comprises an electrical power inverter circuit including a transformer, the elecoluminescent panel resonating with a secondary winding of the transformer. The transformer preferably comprises a ferrite-cored transformer with a centre-tapped primary winding. The turns ratio of the primary winding with respect to the secondary winding is in the range of 1:12 to 1:20 and is preferably in the range 1:16 to 1:17.

The circuit preferably includes a low frequency oscillator operable to cause the light source to flash on and off at a visible rate, a rechargeable battery with associated mains powered charging circuitry, an indicator lamp or LED to indicate the presence of a mains supply voltage and a mains supply voltage detection circuit operable to cause the light source to operate from the battery supply when the mains supply voltage drops below a predetermined level.

One embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block circuit diagram of an emergency light in accordance with the present invention; Figure 2 is a front elevational view of the light, and Figure 3 is an exploded plan view of the light of Figure 2, and Figure 4 is a full circuit diagram of the emergency light of Figure 1.

As shown in Figure 1, an emergency light includes an electroluminescent panel 1 which glows green when energised with an a.c. voltage of the order of 300V at frequencies around 400Hz. This voltage is generated by a power inverter 2 working from a rechargeable battery 3 which is charged, in the presence of a mains supply, by a charging circuit 4. A sensing circuit 5 is arranged to monitor the mains supply connected to an input of the circuit 5 and to turn the inverter 2 on and off as required. Flasher circuit 6 is arranged to switch the inverter on and off at a frequency of the order of 0.5Hz, thereby causing the panel to flash at this frequency.

With reference now to Figures 2 and 3, the light includes a printed circuit board 7 containing the battery and all the necessary circuitry to drive the panel and charge the battery. The electroluminescent panel 1 is sandwiched between the circuit board 7 and a clear plastics arrow 8 forming part of a face plate 9. The sub-assembly of the panel 1, the circuit board 7 and a foam sheet 10 interposed between panel 1 and circuit board 7 is fitted to the face plate 9 using the screws and screw recesses 11 and 12.

Apertures 13 may receive wall mounting screws and are spaced to match threaded lugs in a U.K. 13 Amp double back box.

With reference to Figures 1 and 4 the battery charging circuit 4 comprises a step-down transformer 14, bridge rectifier 15, diode 16 and current limiting resister 17.

When a mains supply is present direct current may flow from the bridge rectifier into the rechargeable battery 3. When the mains supply is no longer present the circuit voltage is maintained by the battery 3, but reverse current flow into the bridge rectifier 15 is blocked by diode 16.

The mains supply voltage sensing circuit 5 uses a voltage divider, comprising resistors 19 and 20, connected to the output of the bridge rectifier 15. When the supply voltage falls, the voltage on the base of a transistor 21 will correspondingly fall. When the supply voltage falls to a predetermined value transistor 21 will conduct sufficiently to allow a multivibrator circuit, consisting of transistors 22, 23, timing resistors 24, 25 and timing capacitors 26, 27, to start to oscillate.

The multivibrator, in combination with a ferrite-cored transformer 28, forms the power inverter 2. The two outputs of the multivibrator are connected to the ends of the primary winding; of transformer 28 and a centre-tap of the primary winding is connected to the positive d.c. supply rail which is an a.c. ground. The capacitive, electroluminescent panel 1 is connected across the secondary of the transformer 28 and forms a resonant circuit with it.

For maximum efficiency the multivibrator is constructed to oscillate substantially at the resonant frequency of the circuit formed by the electroluminescent panel and the transformer secondary.

Optimum panel brightness and battery current drain characteristics have been obtained using a panel voltage of 290V and a frequency of 550Hz. In this case the ferritecored transformer had a turns ratio of 1:16.67 having 384 turns on the primary winding and 6400 turns on the secondary winding.

Flasher circuit 6 consists of a CMOS 555 timer IC 29 and associated timing resistors and capacitors 30, 31, 32, 33.

The output of the timer is connected to the base of a transistor 34. This transistor operates as a semiconductor switch connected in series with the centre-top connection of the transformer 28. When this transistor is in its nonconducting state, the inverter ceases to function and the panel 1 is no longer illuminated. The panel can thus be made to flash at a rate determined by the timer 29.

A non-flashing version of the circuit may be constructed by omitting the timer 29, associated components 30, 31, 32, 33 and transistor 34 and forming a conductive link between the collector and omitter holes, for transistor 34, on the PCB.

An LED 35 serves to indicate the presence of a mains supply.

The circuit described above is a non-maintained circuit which works only in the event of a mains failure but the panel could be driven by a maintained circuit. In the latter case, the panel 1 would always be energised, normally by the mains supply but operating from the battery supply in the event of a mains failure. This can be accomplished with the omission of resister 19.

The light may also be operated from a central battery system.

Claims (22)

1. An emergency indicator light comprising a batterypowered electroluminescent light source and an activating circuit having an input for connection to a mains electricity supply for maintaining the latter and adapted to activate the light source under battery power in the event of a predetermined drop in the mains supply voltage.

2. A light according to claim 1 constructed so that it may be wall-mounted in a room or corridor at skirting board level.

3. A light according to any preceding claim which is of a suitable size to fit entirely in a conventional 13 Amp double back box.

4. A light according to claim 1 or claim 2, comprising the combination of a face plate, an electroluminescent panel mounted behind and parallel to the face plate, and a circuit board mounted parallel and behind the panel.

5. A light according to claim 4, wherein the face plate bears an indicator symbol.

6. A light according to claim 5, wherein the face plate has an aperture shaped in the form of the symbol and includes a light-transmitting cover plate in registry with the aperture.

7. A light according to claim 5 or claim 6, wherein the symbol is an arrow.

8. A light according to any of claims 4, 5 and 6, wherein the circuit board projects behind the face plate, and wherein the face plate includes apertures outside the perimeter of the circuit board for receiving wall-mounting screws.

9. A light according to any preceding claim, wherein the circuit is operable to cause the light source to flash on and off at a visible rate.

10. A light according to any preceding claim, wherein the circuit includes an electrical power inverter for activating the electroluminescent panel.

11. A light according to claim 10, wherein the inverter comprises a multivibrator and a step-up transformer, the transformer having a secondary winding coupled to the panel.

12. A light according to claim 11, wherein the transformer has a centre-tapped primary winding.

13. A light according to claim 12, wherein the circuit includes a semiconductor switch coupled in series with the transformer primary centre-tap connection, the switch being operable repeatedly to cause the light to flash.

14. A light according to claim 13, wherein the switch is coupled between the centre-tap connection and an a.c. ground connection.

15. A light according to any of claims 11 to 14, wherein the panel and the transformer secondary winding form a resonant circuit having a resonant frequency corresponding to the operating frequency of the inverter.

16. A light according to any of claims 11 to 15, wherein the said frequency is in the range of 300Hz to 600Hz.

17. A light according to any of claims 11 to 16, wherein the turns ratio of the transformer is in the range of 1:12 to 1:20, and preferably in the range of 1:16 to 1:17.

18. A light according to any of claims 11 to 17, wherein the transformer has a ferrite core.

19. A light according to any preceding claim, wherein the circuit is arranged such that the panel is not illuminated when a mains supply is present.

20. A light according to any preceding claim, including an integral rechargeable battery and mains charging circuit.

21. A light according to any preceding claim which may be operated from a central battery system.

22. An emergency indicator light constructed and arranged substantially as herein described and shown in the drawings.