GB2466515A

GB2466515A - Security light with a fluorescent lamp

Info

Publication number: GB2466515A
Application number: GB0823566A
Authority: GB
Inventors: Anthony Ottway
Original assignee: GREENLIGHTING Ltd
Current assignee: GREENLIGHTING Ltd
Priority date: 2008-12-24
Filing date: 2008-12-24
Publication date: 2010-06-30
Also published as: GB0823566D0

Abstract

A control circuit for controlling a fluorescent lamp in a security light has a lit mode and a standby mode. The control circuit is arranged so that in the lit mode the light level output by the fluorescent lamp provides illumination, and in the standby mode the fluorescent lamp remains on and struck, but the light level output by the fluorescent lamp does not provide illumination. The control circuit switches the light to lit mode when motion is sensed by a motion sensor, and switches the light to standby mode after a period of time when no motion sensed. If a light sensor senses daylight, the light is switched off. This allows a fluorescent lamp to be used in an application where full brightness is required very quickly after the light is switched on.

Description

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A control circuit for controlling a fluorescent lamp The present invention relates to a control circuit for controlling a fluorescent lamp. The present invention is particularly suitable for controlling a dimmable fluorescent lamp in a security light.

For many years incandescent lamps have been popular for use in domestic and other situations. In an incandescent lamp current is passed through a metal filament, usually made of tungsten. The resistance of the filament to the current causes the filament to heat up, and once the filament is above a certain temperature it will emit light, or "incandesce".

However, the use of fluorescent lamps in place of incandescent lamps is becoming increasingly common. This is because, although fluorescent lamps are more complicated in construction and thus usually more expensive to produce, they are generally more energy efficient and have a longer lifespan. For these reasons fluorescent lamps are often considered more favourable to the environment.

A standard type of known fluorescent lamp is shown in Figure 1. The fluorescent lamp 1 comprises a U-shaped glass tube 2 containing a gas 6 which is a mixture of mercury vapour and an inert gas such as argon at a low pressure (for example around 0.3% of atmospheric pressure) . The inside of the glass tube 2 has a phosphorescent coating of made of a blend of metallic and rare-earth phosphor salts.

The fluorescent lamp 1 has a "ballast" 3, which is an electronic circuit connected to a supply of electricity (such as the standard household or "mains" electricity supply) via electrical connectors 4. The ballast 3 comprises first and second electrodes 5 which are located in the first and second ends of the U-shaped glass tube 2 respectively.

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When the fluorescent lamp 1 is switched on, the ballast 3 initially provides a current through each of the electrodes 5, causing them to heat up and release electrons. These electrons cause the gas 6 in the glass tube 2 to become ionised. The ballast 3 also provides a voltage differential between the electrodes 5, and when the gas 6 is sufficiently ionised an electrical arc is established through the lonised gas 6 between the electrodes 5. The electrical arc excites the atoms of mercury vapour in the gas 6, causing them to emit ultraviolet light. The ultraviolet light is then absorbed by the phosphorescent coating and converted into visible light.

The process of establishing an electrical arc through the gas 6 in the glass tube 2 when it is switched on is known as "striking" the fluorescent lamp 1. After the fluorescent lamp 1 has been struck, the electrical arc through the gas 6 in the glass tube 1 causes it to become increasingly ionised.

This reduces the resistance between the electrodes 5, allowing more current to flow between them. As the current between the electrodes 5 increases, the ultraviolet light emitted by the mercury vapour increases accordingly, and so in turn does the amount of visible light emitted by the fluorescent lamp 1. The ballast 3 acts to control the current between the electrodes 5 so that the current cannot increase indefinitely and damage components of the fluorescent lamp 1.

Ballasts are commonly arranged to control the current so that the fluorescent lamp lights to a pre-determined, fixed level of brightness. However, "dimmable" ballasts are also known. Dimmable ballasts can be used to control the fluorescent lamp so that its level of brightness can be varied. An example of a dimmable ballast is given in WO 2007/04498 (International Rectifier Corporation) published 19 April 2007.

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It is a disadvantage of fluorescent lamps that there can be a long delay between a fluorescent lamp being switched on and the lamp reaching full or near-full brightness. In some cases this delay can be as long as three minutes. This contrasts with incandescent lamps, which may for example reach 90% brightness in much less than half a second.

For this reason, fluorescent lamps are not suitable for situations in which full or near-full brightness is needed very quickly after the lamp has been switched on, and in these cases incandescent lamps are often still used. An example of this is security lighting, where a lamp is switched on in response to movement (for example) being sensed in the local area. It would be desirable to provide a lamp with the advantages in terms of energy efficiency and the environment given by a fluorescent lamp, but without the disadvantage of the long delay between the lamp being switched on and full or near-full brightness being achieved.

In accordance with a first aspect of the present invention there is provided a control circuit for controlling a fluorescent lamp, the control circuit having a lit mode and a standby mode, the control circuit being arranged so that in the lit mode the light level output by the fluorescent lamp provides illumination to the surrounding area, the control circuit being further arranged so that in the standby mode the fluorescent lamp remains on, wherein in the standby mode the light level output by the fluorescent lamp does not provide illumination to the surrounding area.

As the fluorescent lamp remains on in standby mode, when the circuit changes to lit mode there will not be a long delay before fluorescent lamp achieving full or near-full brightness, as the lamp does not need to go through the process of being struck. Also, although in the standby mode the fluorescent lamp is struck, its power consumption is very low. Further, the life of the fluorescent tube is extended, as it is dimmed rather than switched on and off.

Advantageously, the control circuit is arranged to receive a signal from a motion sensor, and wherein the control circuit is arranged to switch from the standby mode to the lit mode when a signal is received from the motion sensor indicating that motion has been detected. Preferably, the control circuit is arranged to switch from the lit mode to the standby mode when no signal is received from the motion sensor indicating that motion has been detected.

Preferably, the control circuit is arranged to wait a pre-determined period before switching from the lit mode to the standby mode. Each of these features allows the control circuit to be used in a security light system.

Advantageously, the control circuit has an off mode, and is arranged such that the fluorescent lamp is switched off when the control circuit is in the off mode. This allows the fluorescent lamp to be switched off when it will not be used for long periods. Advantageously, the control circuit is arranged to receive a signal from a light sensor, wherein the control circuit is arranged to switch to the off mode when the light level detected by the light sensor rises above a pre-determined threshold, and is arranged to switch to the standby mode when the light level detected by the light sensor falls below a pre-determined threshold. This allows light to be switched off during daylight hours, for example.

In accordance with a second aspect of the present invention there is provided a security light comprising: a control circuit as described above; a motion sensor connected to the control circuit; a lamp fixing for the fluorescent lamp controlled by the control circuit.

The lamp fixing may be arranged to take a fluorescent lamp comprising a dimmable ballast. Alternatively, the control circuit comprises a dimrnable ballast, and the lamp fixing is arranged to take a fluorescent lamp without a dimmable ballast.

Advantageously, the security light comprises a light sensor connected to the control circuit.

In accordance with a third aspect of the present invention there is provided a method of operating a security light comprising a dimmable fluorescent lamp and a motion sensor, comprising the steps of: a) striking the fluorescent lamp; b) maintaining a light level output by the fluorescent lamp that does not provide significant illumination to the surrounding area; c) in response to motion being detected by the motion sensor, maintaining a light level output by the fluorescent lamp that provides illumination to the surrounding area; d) in response to no motion being detected by the motion sensor, returning to step b) Advantageously, step d) comprises the substeps: d) in response to no motion being detected by the motion sensor: dl) waiting a pre-determined period of time; d2) returning to step b) Advantageously, the security light further comprises a light sensor, and the method further comprises the steps of: e) in response to the light level detected by the light sensor rising above a pre-determined threshold, switching off the fluorescent lamp; f) in response to the light level detected by the light sensor falling below a pre-determined threshold, returning to step a) In accordance with a fifth aspect of the present invention there is provided a self-contained lamp unit comprising a control circuit as claimed in any of claims 1 to 6, a fluorescent lamp and a dimmable ballast, wherein the self-contained lamp unit is arranged to be retro-fitted in a known security light system.

In accordance with a sixth aspect of the present invention there is provided a control circuit for controlling a fluorescent lamp, the control circuit having a lit mode and a standby mode, the control circuit being arranged so that in the lit mode the fluorescent lamp is maintained at a first light level, and the control circuit being further arranged so that in the standby mode the fluorescent lamp remains on, wherein in the standby mode the output by the fluorescent lamp is maintained at a second light level lower than the first light level.

In accordance with a seventh aspect of the present invention there is provided a security light comprising: a control circuit as described above; a motion sensor connected to the control circuit; a fluorescent lamp controlled by the control circuit; wherein the control circuit is arranged to switch from the standby mode to the lit mode in response to a signal from the motion sensor.

There will now be described embodiments of the invention, with reference to the accompanying drawings of which: Figure 1 shows a known standard type of fluorescent lamp; Figure 2 shows a security light in accordance with a first embodiment of the present invention; Figure 3 is a state chart showing the operation of the security light of the first embodiment; Figure 4 is a circuit diagram of a dimmable ballast for use in the security light of the first embodiment; Figure 5 is a circuit diagram of a voltage transformer for use in the security light of the first embodiment; Figure 6 is a circuit diagram of a control circuit for use in the security light of the first embodiment; Figure 7 is shows a set of security lights in accordance with a second embodiment of the present invention.

A security light in accordance with a first embodiment of the present invention is shown in Figure 2. The security light 100 has a base portion 101 with a fixing 102 on a side exterior surface of the base portion 101 for mounting the security light 100 on a wall of a building, for example.

Inside the base portion 101 there is a control circuit 102, for controlling the operation of the security light 100.

The control circuit 102 is connected to an electrical supply such as the standard household or "mains" electricity supply via a supply cable 104 that passes through the bottom exterior surface of the base portion 101.

A motion sensor 105 is mounted on the opposite side exterior surface of the base portion 101 to the fixing 102.

The motion sensor 105 is for example a microwave sensor, which detects motion by sending out a microwave pulse and measuring the reflection. The motion sensor 105 is in electrical connection with the control circuit 103 via wires 105a. A light sensor 108, for example a "photodarlington" transistor, is mounted on the side exterior surface of the base portion 101 above the motion sensor 105. Similarly, the light sensor 108 is in electrical connection with the control circuit 103 via wires 108a.

On the top exterior surface of the base portion 101 there is a lamp fixing 106 for a fluorescent lamp similar to the lamp 1 shown in Figure 1. However, unlike the fluorescent lamp 1 shown in Figure 1, the fluorescent lamp 107 in the lamp fixing 106 has a diminable ballast 107a. The dimmable ballast 107a in electrical connection with the control circuit 103 via wires 107b connected to the lamp fixing 106. The wires 107b provide the supply of electricity for the ballast 107a. The dimmable ballast 107a is also in electrical connection with the control circuit 103 via wire 107c connected to the lamp fixing 106. The wire 107c provides a control signal from the control circuit 101 to tell the dirnmable ballast 107a the level of brightness at which it should maintain the fluorescent lamp 107.

(In an alternative embodiment the dimmable ballast is part of the control circuit 103, and the lamp fixing 106 is arranged to take a fluorescent lamp without a ballast. In another alternative the lamp fixing 106 takes a fluorescent lamp with a standard non-dimrnable ballast, and the control circuit 103 is arranged to control the brightness level of the fluorescent lamp by varying the power level it supplies to the ballast.) A transparent cover 109 is mounted on the top exterior surface of the base portion 101 over the lamp fixing 106 and fluorescent lamp 107 to protect it from outside conditions, for example rain and the like.

The operation of the security light 100 is shown in the state chart of Figure 3. The operation of the security light is controlled by the control circuit 103, which controls the fluorescent lamp 107 based on the input it receives from the motion detector 105 and light detector 108, amongst other things. When the security light is first switched on, the control circuit 103 powers on the fluorescent lamp 107 at full power for 30 seconds. The control circuit 103 then controls the fluorescent lamp 107 in accordance with the signals it receives from the light sensor 108 and motion sensor 105.

In the state chart of Figure 3, initially the security light 1 is in state 200, in which the fluorescent lamp 107 is

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off. The security light 100 will remain in this state while the light level detected by the light sensor 108 remains above a pre-determined level (indicating, for example, that it is day-time) When the light level detected by the light sensor 108 falls below the pre-determined level, for example 70 lux (lumens per square metre) , (transition 210) (indicating, for example, that night has fallen) , the fluorescent lamp 107 is struck (action 220) . The control circuit 103 then dims the fluorescent lamp 107 to its minimum brightness level, so that the security light 100 is in state 201. In this state, although the fluorescent lamp 107 is on, it is generating no useful light, and is using only a very small amount of power.

If, while in state 201, motion is detected by the motion sensor 105 (transition 211), the control circuit 103 switches the fluorescent lamp 107 to its maximum brightness level (state 202) . As the fluorescent light 107 has already been struck, and so the gas in the glass tube of the fluorescent light 107 has already been ionised and the electrical arc between the electrodes of the fluorescent light 107 has been established, the fluorescent light 107 is able to reach full or near-full brightness level very quickly, say within one second.

When motion is no longer detected (transition 212), the control circuit 103 waits a pre-determined period of time (action 221) (for example 5 minutes), and then dims the fluorescent lamp 107 back to its minimum state, returning the security light 100 to state 201.

The security light 100 will remain in state 201 while the light level detected by the light sensor 108 remains below the pre-determined level. If the light level detected by the light sensor 108 rises above the pre-determined level (transition 213) (indicating, for example, a new day has begun), the control circuit 100 switches the fluorescent lamp 107 off, returning the security light 100 to state 200.

The control circuit 103 may also be arranged to switch the fluorescent lamp 107 off when the light level detected by the light sensor 108 rises above the pre-determined level when the security light 100 is in state 202, so retuning the security light to state 200, even if motion is still being detected by the motion sensor 105.

A circuit diagram of the dimmable ballast 107a is shown in Figure 4. As described above, the dimmable ballast 107a in electrical connection with the control circuit 103 via wires 107b, which provide the supply of electricity for the ballast 107a. The dimmable ballast 107a is also in electrical connection with the control circuit 101 via wire 107c, which provides a control signal from the control circuit 101 to tell the dimmable ballast 107a the level of brightness at which it should maintain the fluorescent lamp 107.

Circuit diagrams for the control circuit 103 are shown in Figures 5 and 6. Figure 5 is a circuit diagram of a voltage converter 103a for the control circuit 103, which converts the "mains" electricity supply from the supply cable 104 into a 5 volt supply. Figure 6 is a circuit diagram of the control circuitry itself. The control circuitry is powered by the 5 volt supply generated by the voltage converter 103a. A first part 103b of the control circuitry provides a signal with the appropriate behaviour according to states 201 and 202 of the state chart of Figure 3 in response to signals from the motion sensor 105. A second part 103c of the control circuitry provides a signal with the appropriate behaviour according to states 201 and 202 of the state chart of Figure 3 in response to signals from the light sensor 108.

These signals are combined by a third part 103d of the control circuitry to provide the required control signal via wire 107c to the fluorescent lamp 107.

Figure 7 is shows a set of security lights in accordance with a second embodiment of the present invention. Each of the security lights 200, 201, 202 is a self-contained unit comprising a fluorescent lamp, dimrnable ballast and control circuit similar to those described above. Each of the security lights 200, 201, 202 is powered by a "mains" power supply consisting of a live supply 210 and neutral supply 211. The operation of the security lights 200, 201, 202 is controlled by a control line 212, which comprises a variable resistor 215 by which the minimum brightness level of the security lights can be adjusted. The security lights can be either "master" or "slave" lights, where a slave light is controlled via the control line 212 by a signal from a master light. More than one master light can be used on a single circuit, and in Figure 7 security lights 200 and 201 are master lights, while security light 202 is a slave light.

Claims

Claims: 1. A control circuit for controlling a fluorescent lamp, the control circuit having a lit mode and a standby mode, the control circuit being arranged so that in the lit mode the light level output by the fluorescent lamp provides illumination to the surrounding area, the control circuit being further arranged so that in the standby mode the fluorescent lamp remains on, wherein in the standby mode the light level output by the fluorescent lamp does not provide illumination to the surrounding area.
2. A control circuit as claimed in claim 1, wherein the control circuit is arranged to receive a signal from a motion sensor, and wherein the control circuit is arranged to switch from the standby mode to the lit mode when a signal is received from the motion sensor indicating that motion has been detected.
3. A control circuit as claimed in claim 2, wherein the control circuit is arranged to switch from the lit mode to the standby mode when no signal is received from the motion sensor indicating that motion has been detected.
4. A control circuit as claimed in claim 3, wherein the control circuit is arranged to wait a pre-determined period before switching from the lit mode to the standby mode.
5. A control circuit as claimed in any of claims 2 to 4, the control circuit having an off mode, the control circuit being arranged such that the fluorescent lamp is switched off when the control circuit is in the off mode.
6. A control circuit as claimed in claim 4, wherein the control circuit is arranged to receive a signal from a light sensor, wherein the control circuit is arranged to switch to the off mode when the light level detected by the light sensor rises above a pre-determined threshold, and is arranged to switch to the standby mode when the light level detected by the light sensor falls below a pre-determined threshold.
7. A security light comprising: a control circuit as claimed in any of claims 2 to 6; a motion sensor connected to the control circuit; a lamp fixing for the fluorescent lamp controlled by the * control circuit.
8. A security light as claimed in claim 7, wherein the lamp fixing is arranged to take a fluorescent lamp comprising a dimmable ballast.
9. A security light as claimed in claim 7, wherein the control circuit comprises a dimmable ballast, and the lamp fixing is arranged to take a fluorescent lamp without a dimmable ballast.
10. A security light as claimed in any of claims 7 to 9, further comprising a light sensor connected to the control circuit.
11. A method of operating a security light comprising a dimmable fluorescent lamp and a motion sensor, comprising the steps of: a) striking the fluorescent lamp;Ib) maintaining a light level output by the fluorescent lamp that does not provide significant illumination to the surrounding area; C) in response to motion being detected by the motion sensor, maintaining a light level output by the fluorescent lamp that provides illumination to the surrounding area; d) in response to no motion being detected by the motion sensor, returning to step b)
12. A method as claimed in claim 11, wherein step d) comprises the substeps: d) in response to no motion being detected by the motion sensor: dl) waiting a pre-determined period of time; d2) returning to step b)
13. A method as claimed in claim 11 or claim 12, wherein the security light further comprises a light sensor, and the method further comprises the steps of: e) in response to the light level detected by the light sensor rising above a pre-determined threshold, switching off the fluorescent lamp; f) in response to the light level detected by the light sensor falling below a pre-determined threshold, returning to step a)
14. A self-contained lamp unit comprising a control circuit as claimed in any of claims 1 to 6, a fluorescent lamp and a dimmable ballast, wherein the self-contained lamp unit is arranged to be retro-fitted in a known security light system.
15. A control circuit for controlling a fluorescent lamp, the control circuit having a lit mode and a standby mode, the control circuit being arranged so that in the lit mode the fluorescent lamp is maintained at a first light level, and the control circuit being further arranged so that in the standby mode the fluorescent lamp remains on, wherein in the standby mode the output by the fluorescent lamp is maintained at a second light level lower than the first light level.
16. A security light comprising: a control circuit as claimed in claim 15; a motion sensor connected to the control circuit; a fluorescent lamp controlled by the control circuit; wherein the control circuit is arranged to switch from the standby mode to the lit mode in response to a signal from the motion sensor.