GB2326473A - Fluorescent lighting system with ambient light detector - Google Patents

Abstract

A fluorescent lighting system in which the light 10 is periodically deactivated whilst the ambient light intensity is sensed by a detector 52. If the ambient light level is too low then the fluorescent light is reactivated sufficiently quickly to prevent cooling of the coils 10a, 10b which would shorten the life of the fluorescing means.

Description

"Lighting System" The present invention relates to a lighting system.

Conventionally, security lighting has been controlled by one of two methods. The first is more commonplace within a property and involves the light being connected to some form of timer switch. Generally, the timer switch is set to switch the light on at some preset time and subsequently switch off after a predefined time interval, or at a second preset time.

The second type is generally used outwith the property and utilises a photocell detector to sense when darkness falls. Upon sensing the level of light using the detector, the light will be switched on and off as required.

Modern lights are now being manufactured as high efficiency fluorescent tubes which have a ballast, mounted within a connector housing. The housing is conventionally the section of the light which is fitted into the respective connector at the light fitting.

The ballast is used to control the amount of current which is supplied to the tube of the light.

This type of fluorescent light has a drawback which becomes relevant when automatic control is desired.

The coils within the tube of the light are preferably pre-heated to a certain temperature before the light is activated. This helps to reduce undue wear of the tube.

Some form of ambient light detector may be used to facilitate automatic control of the light. The detector may sample the condition of light at periodic intervals. The easiest way to do so is to use the detectors as described above. However, these units and their associated circuitry are relatively large and cannot be mounted in a small area, such as the connector housing of the light.

Traditional visible light detectors would require the light to be switched off before the detector could sample ambient light levels, as light emitted from the light itself would adversely affect the result.

However, periodic switching off and on of a light of this type must be achieved in as short a time as possible to prevent the coils of the light from cooling.

However, this switch-off time is typically long enough to be detectable by the human eye and as such becomes annoying and distracting when the on-off-on cycle is repeated frequently, say every two minutes.

According to the present invention there is provided a lighting system comprising fluorescing means having at least one coil; a light detector for detecting the level of ambient light and producing a signal corresponding thereto; and a controller for operating the fluorescing means, wherein the controller includes computer software programmed to periodically deactivate the fluorescing means, detect the signal from the light detector and reactivate the fluorescing means in response to the signal, the duration of such deactivation being insufficient to allow substantial cooling of the electrodes.

The system typically includes a delay means for delaying the activation of the fluorescing means for a period of time.

The delay means typically comprises a driver circuit which is arranged to apply a first, relatively high, frequency to the fluorescing means during an initial period and a second, relatively low, frequency thereafter.

Preferably, the system further includes a frequency controller. The frequency controller typically controls the change in frequency between the first frequency and the second frequency. Preferably, the frequency controller sweeps all frequencies between the first and second frequencies. The frequency controller typically comprises a frequency sweep circuit.

The fluorescing means typically comprises a fluorescent tube, where the coil typically forms part of the tube.

The computer software is typically retrievably stored in a microprocessor, wherein the microprocessor decodes and executes commands contained within the software.

Typically, the software is programmable to alter the periodicity of the deactivation of the fluorescing means.

The software is typically programmable to alter the periodicity in a user-specific manner wherein the microprocessor is supplied with an input to which the software is programmed to respond, the parameters of the input being determined by a user.

Typically, the software is programmed to respond to a plurality of inputs to the microprocessor, the inputs allowing a user to set the brightness of the fluorescing means and the length of time of activation of the fluorescing means.

Preferably, the light detector comprises a light dependent resistor, the resistor being electrically connected to the microprocessor for providing an input thereto which is proportional to the level of ambient light.

Optionally, the system may further include an energy and/or heat saver circuit. The energy and/or heat saver circuit typically comprises a linear voltage regulator.

The controller is preferably located within a housing, and the frequency controller, delay means, light detector and energy and/or heat saver circuit are preferably also located in the housing. The housing typically comprises a connector housing.

The fluorescing means typically has two coils.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which Fig. 1 is a flow diagram showing the stages of a software program for use with the present invention; Fig. 2 is a schematic representation of an electronic circuit for use with the present invention; and Fig. 3 is a schematic representation of an alternative electronic circuit for use with the present invention.

Referring to Fig. 2 there is shown a lighting system according to the present invention, the system including a fluorescent light 10. The light 10 is of the high efficiency type in which there are two coils 10a, 10b, connected in series through a capacitor 12.

As is well known in the art, this type of light is manufactured with a base (not shown) through which the light 10 can be connected to an electric power source.

This base preferably houses the circuit shown in Fig.

2. It will be appreciated that this type of light 10 requires the coils 10a, 10b to be pre-heated before light is emitted therefrom to prevent undue wear of the coils 10a, 10b.

The light 10 is connected to a half-bridge driver integrated circuit 14. The driver 14 is operated at high frequency for an initial period, the frequency of which is determined by a resistor-capacitor (RC) timer circuit, generally designated as 16. Within this timer circuit 16 is a resistor 18, a first capacitor 20 and a second capacitor 22. Both of the capacitors 18, 20 are initially used to determine the frequency of the high frequency.

After this initial period, the RC timer circuit 16 is adjusted so that the second capacitor 20 is no longer in the circuit. A dual-digital transistor IC 24 may be used to effectively ground the second capacitor 20, thus removing it from the RC timer circuit 16. This change in capacitance shifts the frequency down, and a voltage across the capacitor 12 rises rapidly. This rise in voltage causes the light 10 to strike, as is well known in the art, due to the potential difference developed across the coils 10a, 10b as a result of the high impedance provided by the capacitor 12.

Fig. 3 shows a similar circuit to that of Fig. 2 with a number of modifications. Where possible, like reference numerals and component numbers have been used to designate similar components in both figures.

The first modification involves the removal of the dual-digital transistor IC 24 which was used to control the change in frequency between the pre-heat phase and the operational phase of the light 10. The upper transistor in the IC 24 has been replaced with a discrete transistor 60 and resistor 62. The other transistor in the dual-transistor IC 24 has been replaced with a discrete transistor 64 and resistor 66.

A capacitor 68 is located between the base and emitter of the transistor 64. The capacitor 68 acts to smooth the step output from OV to 5V of the microprocessor 26 (pin 6 as shown in Fig.3). The voltage across the base-emitter of transistor 64 increases slowly with an RC time constant given by the values of resistor 66 and capacitor 68. In response to this, the voltage across the collector-emitter of the transistor 64 decreases slowly.

The decrease in collector-emitter voltage causes a slow decrease in the voltage across a zener diode 70. It should be noted that the diode 70 replaces the capacitor 22 in Fig. 2.

The decrease in voltage across the diode 70 causes the frequency of the oscillator in the half-bridge driver 14 to change slowly from the pre-heat frequency (relatively high) to the running or operating frequency (relatively low). As the oscillator frequency is changing slowly, substantially all frequencies between the pre-heat frequency and the running frequency are set. This sweep in frequency allows the voltage across the resonant capacitor 12 (in series between the two coils 10a, 10b) to increase as the output frequency from the driver 14 approaches the resonant frequency of the inductor-capacitor (LC) circuit formed by an inductor 72 and the capacitor 12. Once a high enough voltage has been developed across capacitor 12, the light 10 will strike.

Without the addition of the frequency sweep circuit (generally designated 74), the oscillator in the driver 14 may not operate near this resonant frequency and the high voltages required to strike the light 10 may not be achieved. This may cause problems in high power lights which require higher strike voltages, and also at low temperatures where all light types require higher strike voltages than at room temperature.

The second modification is the addition of an energy and/or heat saving circuit, generally designated as 80.

The circuit 80 consists of two resistors 82, 84 in series, a zener diode 86 and a transistor 88, which form a linear voltage regulator. When power is applied to the circuit (through connections 90, 92), power is supplied to the driver 14 and the microprocessor 26 through a resistor 94. Note that the bridge rectifier 54 in Fig. 2 has been replaced by a voltage regulator 96 in the circuit of Fig. 3.

The voltage on the supply pin (pin 1) of the driver 14 rises, and when this voltage exceeds the threshold voltage of the driver 14, oscillation begins as described above. The oscillation drives the output field effect transistors (FETs) contained within the driver 14, which in turn strikes the light 10. From the output of the driver 14 (pin 6), a charge pump circuit, generally designated 100, supplies power to the supply pin (pin 1) of the driver 14.

The charge pump circuit 100 consists of a capacitor 102 which acts as a DC block and also limits the current, and two diodes, designated 104, which rectify the oscillations from the output pin (pin 6) of the driver 14.

The charge pump circuit 100 increase the voltage at the supply pin (pin 1) of the driver 14 to the maximum possible voltage due to an internal zener diode within driver 14. This voltage is equal to, or higher than, the voltage across the zener diode 86. Thus, with no potential difference across the base-emitter junction of the transistor 88, it switches off, reducing the current flow through the resistor 94. The charge pump circuit 100 is used to take some of the load from the power resistor 94 which reduces the current going through it. This reduction in current consequently produces a reduction in the amount of heat which the resistor is required to dissipate and thus reduces the operating temperature, and reduces the amount of current drawn from the power supply (ie supplied through the connections 90, 92).

However, when the oscillator (in driver 14) is stopped by the microprocessor 26 (for example when the level of light detected by the LDR 52 is above, say, 5 lux), the charge pump circuit 100 can no longer supply power to the system. Thus, the voltage at the supply pin (pin 1) of the driver 14 falls below the voltage of the zener diode 86 by approximately 2 volts. The voltage across the base-emitter junction of the transistor 88 increases sufficiently to turn it on, and power is again supplied to the system via the resistor 94.

To provide for automatic control of the light 10 and to increase the functionality thereof, a microprocessor 26 is used which has an integral programmable read only memory (PROM). A software program is retrievably stored within the PROM and provides for control of the system.

Note that the circuit shown in Fig. 2 has a digital transistor 56 and associated circuitry. This transistor 56 was used as a reset if the system began to "brown out". Brown out relates to the situation where the supply voltage drops below the nominal operating level for a period of time. In the event of a brown out, the digital transistor 56 (as in Fig. 2) creates a short to pin 4 of the microprocessor 26, thereby resetting the system. The brown out reset is now incorporated as part of the software which controls the system.

Referring now to Fig. 1, there is shown the functional flowchart of the software program which may be stored in the PROM contained within the processor 26. To ease reference, each of the states which the program will go through has been given an associated reference numeral.

The initial starting point is where the light is off at state 28. When the system receives a command to switch the light 10 on, it will begin to power up and move to state 30. It will then initialise the microprocessor 26 at state 32, the initial transition from power up 30 to initialising the microprocessor 26 (at state 32) taking a period of A milliseconds (ms).

After a period of B ms, the system will begin to preheat the coils 10a, 10b at state 34, which will take a further C ms. Once the coils 10a, 10b are preheated to the proper operating temperature, the light will come on for a period as depicted by D seconds in state 36. This can be set, using the software, to be any selected length of time.

This particular parameter has applications where the light may be on in a child's bedroom, and the parent may wish to operate the light as a nightlight. The period D seconds could be set to keep the light on for say half-an-hour, after which the light 10 is switched off automatically at state 38.

If required, the system will check the level of ambient light at state 40 over a short period of E ms (typically 40 ms). The heat in the coils 10a, 10b will rapidly dissipate while the light 10 is off, and if the light 10 is to be reactivated after the ambient light level is checked, this must be done before the coils 10a, 10b cool sufficiently to necessitate having to preheat them again. The level of ambient light at state 40 is detected by means of a change in resistance of the light dependent resistor (LDR) 52, as shown in Figs 2 and 3.

A switch off period in the order of 40 ms is detectable by sight and would cause annoyance if repeated frequently. Thus, it is preferable to have the intervals between checking the level of ambient light preset to minimise this effect. This is particularly applicable to situations where the light is being used indoors. For outdoor use, this is not so important.

Having checked the level of ambient light at state 40 using LDR 52, if the input to the microprocessor 26 remains at a level which indicates sufficient ambient light, then the light 10 will remain off as at state 42. The cycle will continue checking the light level at state 40 until the input voltage at the microprocessor 26 corresponds to the pre-determined threshold level which indicates insufficient ambient light.

Once the system has detected that the ambient light level has fallen below this predefined threshold level, the system queries whether or not the light 10 was lit before the check is made at state 44. If the light 10 was not lit, the coils 10a, 10b are preheated for C ms at state 46 (similar to the preheating at state 34).

If the light 10 was lit, then this preheating state 46 is not required.

The next state is to have the light 10 on for a predetermined time period of F minutes at state 48.

This allows for a number of possible applications. For example, F could be set to a long predetermined time, such as say 360 minutes (representing 6 hours), as once the onset of dusk has been detected, it follows that it will remain dark for a substantial period of time.

After the predetermined time period F, the system returns to states 38 to 48 where the light 10 is temporarily switched off and the level of light checked periodically as described above.

The software may be programmed either in advance or on demand by the user, so that the value of F is variable.

After an initial value of (say) 360 minutes, subsequent values of (say) 15 minutes may be provided to allow for more frequent detection of ambient light level as dawn approaches.

A further option available to the user may be to adjust the brightness of the light 10. This is advantageous when the light 10 is being used as a nightlight, where it would be undesirable for it to provide full illumination.

Further, if the light 10 is used to illuminate an advertising sign or the like, the intensity of the light 10 may require to be adjusted. During daylight, the light 10 burns with full intensity to ensure that the sign is clearly visible against ambient light conditions. Conversely, during the night (or in darker conditions due to adverse weather for example) the sign need not be so bright as the ambient light intensity is significantly reduced. This change would be detected by the LDR 52 and the intensity could consequently be automatically adjusted at preset intervals, The brightness could also be manually adjusted by providing a suitable input to the microprocessor 26.

The light 10 may also be used in a simple timedependent mode where it switches on at a predetermined time and then switches off after a few hours, for example, for security purposes; the times may be altered at random or by specifically preprogramming the variable D.

It should be noted that the processor 26 may be replaced by a processor of the type with an integral erasable programmable read only memory (EPROM). This would allow the lighting system to be programmed depending upon user requirements. The processor 26 could additionally be replaced by one where the user may input certain parameters to adjust the functionality of the light 10, such as those described hereinbefore.

Hence, there is provided a lighting system which is versatile and includes scope for use in a wide variety of applications.

Modifications and improvements may be made to the foregoing, without departing from the scope of the invention.

Claims (23)

1. A lighting system comprising fluorescing means having electrodes; a light detector for detecting the level of ambient light and producing a signal corresponding thereto; and a controller for operating the fluorescing means, wherein the controller includes computer software programmed to periodically deactivate the fluorescing means, detect the signal from the light detector and reactivate the fluorescing means in response to the signal, the duration of such deactivation being insufficient to allow substantial cooling of the electrodes.

2. A lighting system according to claim 1, further including a delay means for delaying the activation of the fluorescing means for a period of time.

3. A lighting system according to claim 2, wherein the delay means comprises a driver circuit which is arranged to apply a first, relatively high, frequency to the fluorescing means during an initial period and a second, relatively low, frequency thereafter.

4. A lighting system according to claim 3, wherein the system further includes a frequency controller, wherein the frequency controller controls the change in frequency between the first frequency and the second frequency.

5. A lighting system according to claim 4, wherein the frequency controller sweeps all frequencies between the first and second frequencies.

6. A lighting system according to any preceding claim, wherein the computer software is retrievably stored in a microprocessor, wherein the microprocessor decodes and executes commands contained within the software.

7. A lighting system according to any preceding claim, wherein the software is programmable to alter the periodicity of the deactivation of the fluorescing means.

8. A lighting system according to claim 7, wherein the software is programmable to alter the periodicity in a user-specific manner.

9. A lighting system according to any preceding claim, wherein the software is programmable to allow a user to set the brightness of the fluorescing means

10. A lighting system according to any preceding claim, wherein the software is programmable to allow a user to adjust the length of time of activation of the fluorescing means.

11. A lighting system according to any preceding claim, wherein the light detector comprises a light dependent resistor.

12. A lighting system according to claim 12 when dependent upon claim 6, wherein the light dependent resistor is electrically connected to the microprocessor for providing an input thereto which is proportional to the level of ambient light.

13. A lighting system according to any preceding claim further including an energy and/or heat saver circuit.

14. A lighting system according to claim 13, wherein the energy and/or heat saver circuit comprises a linear voltage regulator.

15. A lighting system according to any preceding claim, wherein the controller is located within a housing.

16. A lighting system according to any one of claims 4 to 15, wherein the frequency controller is located within a housing.

17. A lighting system according to any one of claims 2 to 16, wherein the delay means is located within a housing.

18. A lighting system according to any one of claims 13 to 17, wherein the energy and/or heat saver circuit is located within a housing.

19. A lighting system according to any preceding claim, wherein the light detector is located within a housing.

20. A lighting system according to any one of claims 15 to 19, wherein the housing comprises a connector housing.

21. A lighting system according to any preceding claim, wherein the fluorescing means comprises a fluorescent tube.

22. A lighting system according to any preceding claim, wherein the fluorescing means has two coils.

23. A lighting system substantially as hereinbefore described with reference to the accompanying drawings.