GB2194399A - Fluorescent light control circuits: refrigerated cabinets - Google Patents

Abstract

The control circuitry causes a first voltage to be applied to the fluorescent light (18, 20), (Fig. 1), for a predetermined time sufficient to allow the light to reach a stable operating state, whereafter a second voltage, lower than the first voltage, is applied to the light. The use of such circuitry permits high efficiency fluorescent tubes to be used in, for example, refrigerated cabinets, (Fig. 1), where high levels of illumination are not required, and also reduces the heat output from the tubes. When a timer 38 times out, a circuit IC3 energises a relay RL1 or RL2 to switch the light supply from a direct mains connection to one or the other of two lower voltage taps 60, 62 providing a choice of two values for the second voltage in dependence on the state of a logic control input 36 which may be applied manually or by an energy management system. The tubes may be shielded against air turbulence within the refrigerated cabinet by strips of transparent material. <IMAGE>

Description

SPECIFICATION Fluorescent lighting control This invention relates to the control of fluorescent lighting, and is particularly, although not exclusively, concerned with the control of fluorescent lighting in refrigerated display cabinets in shops and supermarkets.

It is conventional for refrigerated cabinets containing food to be lit by means of internal fluorescent lights. Such lighting makes the display look more attractive, and assists customers in finding the items which they want. However, the lighting also has disadvantages. Firstly, the fluorescent tubes give off heat, which in turn increases the power consumption of the refrigeration unit. Secondly, light has a deleterious effect on many foods. Because of these disadvantages, it is sensible for the lighting to be kept at a relatively low level.

Recently, considerable progress has been made in improving the efficiency of fluorescent tubes. In particular, high efficiency fluorescent tubes are available which give much greater intensity of illumination than the more conventional type of fluorescent tubes, for the same power consumption. Thus, while the replacement of conventional tubes by high efficiency tubes would reduce the power required for lighting refrigerated cabinets, the accompanying increased intensity of illumination would make the disadvantages worse.

According to the present invention there is provided control circuitry for a fluorescent light, the circuitry being adapted to cause a first voltage to be applied to the fluorescent light for a predetermined time sufficient to allow the light to reach a stable operating state, whereafter a second voltage, lower than the first voltage, is applied to the light.

The predetermined time may be in the range 3 to 10 minutes, preferably 4 to 6 minutes. At the end of this time, the fluorescent light will have reached its operating temperature, and the reduction in voltage will merely reduce the intensity of illumination, without causing flicker or extinguishing of the light.

The first voltage may be the mains supply voltage, and the second voltage may be 60 to 80% of the first voltage. In a preferred embodiment, the value of the second voltage may be selected from two or more possible values, so that the intensity of illumination can be selected to suit prevailing circumstances.

The circuitry preferably comprises a timer circuit controlling the operation of one or more relays for switching the output of the circuitry between the first voltage and the or each second voltage. The second voltage or voltages may be established by means of a potentiometer.

The circuitry is particularly applicable to fluorescent lights in a refrigerated cabinet, and accordingly a further aspect of the present invention provides a refrigerated cabinet comprising at least one fluorescent light disposed within the cabinet for illuminating the interior of the cabinet, the light being controlled by control circuitry as defined above.

Preferably, the or each fluorescent light is shielded against air turbulence within the cabinet, in order to prevent undesired cooling of the fluorescent tube. The shielding may, for example, comprise a strip of perspex or other transparent material disposed adjacent the tube.

For a better understanding of the present invention, and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagrammatic sectionai view of a refrigerated cabinet provided with fluorescent lights; and Figure 2 is a circuit diagram representing control circuitry for the lights of the cabinet of Fig.

1.

Referring to Fig. 1, the cabinet comprises a body 2 supported on legs 4. The body 2 comprises a base 6, a rear wall 8, a roof 10 and a front wall 12. Shelves 14 are fixed to the rear wall 8. A canopy 16 is provided at the front end of the roof 10.

The canopy 16 accommodates two fluorescent light tubes 10, and further fluorescent light tubes 20 are provided underneath the shelves 14 at their front ends. The light tubes are high efficiency fluorescent tubes such as those available from Phillips under the designation TLD30W/83.

The operation of the tubes 18 and 20 is controlled by control circuitry accommodated in a control box 22 which is situated beneath the floor 6 of the cabinet. It will be appreciated that the control box 22 could be situated elsewhere, for example on the roof 10 of the cabinet.

The circuitry contained in the control box 22 is shown in Fig. 2. Mains supply is fed to the control box 22 through a cable comprising live and neutral leads 24 and 26. The lead 24 is provided with an on/off switch 28. A potentiometer 30 is connected across the leads 24 and 26, and a tapping 31 applies a 6.5 volt potential difference across a rectifier 32. The output of the rectifier 32 is smoothed and stabilised by a capacitor C1 and a voltage regulator 34 to produce a stabilised output of 5 volts.

The output of the voltage regulator 34 is applied to a logic control input 36 (which will be described later) and to a timing circuit 38. The timing circuit 38 comprises two transistors 40 and 42 which are coupled together as a darlington pair. The collectors of the transistors 40 and 42 are connected to the output of the voltage regulator 34 through a resistor R5, while the base of the transistor 40 is connected to the output of the voltage regulator 34 through a resistor R4.

The base of the transistor 40 is connected to earth through a capacitor C2. The base of the transistor 40 is also connected to earth through a diode 44 and a resistor R3. The connection between the diode 44 and the resistor R3 is connected to the output of the voltage regulator 34 through a resistor R2.

The connection between the resistor R5 and the collectors of the transistors 40 and 42 is connected to one input of an OR gate 46, and to one input of an OR gate 48. The other input of the OR gate 46 is connected through a resistor R, to the output of the voltage regulator 34.

The other input of the OR gate 48 is connected to the output of an inverter 50, the input of which is connected through the resistor R1 to the output of the voltage regulator 34.

The output of the OR gate 46 is connected through an inverter 52 to one input of an integrated circuit IC3, and the output of the OR gate 48 is connected to an input of the integrated circuit IC3 through an inverter 54. The integrated circuit IC3 has connections to earth and to respective relays RL1 and RL2 which control switches 56 and 58. The switch 56 is movable selectively between the output of the switch 28 and a tapping 60 of the potentiometer 30, and the switch 58 is movable between the output of the switch 56 and a tapping 62 of the potentiometer 30. The output of the switch 58 is connected to the live lead 64 of the lighting circuits.

The logic control input 36 is connected by an optoelectronic interface 66 to the connection between the resistor R1 and the common input to the OR gate 46 and the inverter 50. Thus, in one state of the logic control input 36, that connection is earthed, while in the other state it is at the output potential of the voltage regulator 34. Thus, depending on the state of the logic control input 36, either a high or a low signal may be applied to the input of the inverter 50 and the second input of the OR gate 46. The logic control input 36 may be controlled manually, or by an energy management system. Power for driving the logic control input 36 is obtained from the output of the voltage regulator 34.

In the inactive state of the lighting circuit, with the fluorescent lights extinguished, the switches 56 and 58 are in the positions indicated in Fig. 2. To illuminate the lights, the switch 28 is closed, and this initially causes the mains supply voltage (240 volts) to be supplied to the lighting circuitry through the switches 56 and 58. At the same time, the 5V smoothed and rectified output from the voltage regulator 34 is applied to the capacitor C2, which begins to charge. Initially, the voltage at the base of the transistor 40 is insufficient to make the darlington pair 40 and 42 conductive, with the result that the connection between the resistor R5 and the collectors of the transistors 40 and 42 is at a high level.Consequently, both inputs to the integrated circuit IC3 are at a low level, and the relays RL1 and RL2 are inactive.

When the capacitor C2 has charged sufficiently, that is when the voltage at the base of the transistor 40 exceeds the sum of the base-emitter voltages of the darlington pair 40, 42 (approximately 1.4 volts), the transistors 40 and 42 will conduct, and the voltage at the connection between the resistor R5 and the collectors of the transistors 40, 42 will fall to a low level. As a result, one of the inputs of the integrated circuit IC3 will be at a high level, depending on the condition of the logic control input 36. This will cause one of the relays RL1 and RL2 to be energised, so changing over one of the switches 56 and 58.

If the switch 56 is changed over, the voltage at the tapping 60 will be applied to the lighting circuit along the lead 64 through the switches 56 and 58. If the relay RL2 is energised, the voltage of the tapping 62 will be applied to the lead 64 of the lighting circuit through the switch 58.

By way of example, the voltage of the tapping 60 may be approximately 185 volts, while the voltage at the tapping 62 may be approximately 170 volts. Thus, after a predetermined time of, for example, five minutes, as established by the timing circuit 38, the voltage applied to the lighting circuits will fall from the mains voltage of 240 volts to either 185 volts or 170 volts, depending on the condition of the logic control input. The voltage applied to the lighting circuits will govern the intensity of the light emitted by the fluorescent tubes.

In the event of power failure, either deliberate or unintentional, the voltage at the junction between the resistors R2 and R3 will fall faster than that at the junction between the resistor R4 and the capacitor C2. Once the voltage at the junction between resistors R2 and R3 has fallen below that at the junction between the resistor R4 and the capacitor C2 by an amount equal to the forward bias of the diode 44, the capacitor C2 will discharge through the diode 44 and the resistor R3. This will reduce the voltage at the base of the transistor 40, and eventually the transistors 40 and 42 will cease to conduct, with the result that the relays RL1 and RL2 will both be de-energised. If, at this stage, power is resumed, the full mains voltage will initially be applied to the lighting circuits, until the capacitor C2 has recharged. Should power be resumed before the capacitor C2 has discharged far enough to cause the transistors 40 and 42 to become non-conductive, the voltage applied to the lighting circuits will be the same as that immediately before power was disconnected.

It will be appreciated that, should power be resumed after the darlington pair 40, 42 have become non-conductive, but before the capacitor C2 has discharged completely, the time during which the lighting circuits are supplied with full mains voltage will be reduced.

It will be appreciated that the performance of the fluorescent tubes 18 and 20 will be affected by temperature. This is particularly evident if turbulence within the cabinet causes a flow of cold air across the tubes 18 or 20, so as to produce a cooling effect. Under such circumstances, the tubes 18 and 20 may flicker. This effect can be avoided by screening the tubes 18 and 20 from turbulence by means of strips of perspex (RTM) or other transparent material.

It will be appreciated that many variations can be made in the control circuitry shown in Fig.

2. For example, the darlington pair 40 and 42 and the resistor R5 could be replaced by a comparator having one input connected to the junction between the resistor R4 and the capacitor C2 and the other input connected to the junction between the diode 44 and the resistor R3.

Also, for example, the potentiometer 30 could be replaced by a transformer having two secondary coils, one of which supplies an AC voltage to the rectifier 32, and the other of which supplies an AC voltage of 185 volts to the switch 56 with a tapping supplying a voltage of 170 volts to the switch 58.

By way of example, a practical embodiment in accordance with the present invention was compared with a conventional lighting system using argon-filled fluorescent tubes available under the designation TLD32. The system in accordance with the present invention utilised high efficiency tubes available under the designation TLD83. The test was conducted on a dairy cabinet running with an internal temperature of 0 C. The cabinet was provided with nine lamp fittings. The object of the test was to provide a comparative indication of the power consumption of the krypton filled tubes, run at reduced voltage, when producing the same illumination intensity as the argon-filled tubes run at mains voltage. The results are indicated in the table below: CONVENTIONAL TUBES MCFE32 Mains Lamp Total Voltage Voltage Current Light O/P V.A.

240 240 3.4 amps 1150Lux 816 HIGH EFFICIENCY TUBES TLD83 Mains Lamp Total Voltage Voltage Current Light O/P V.A.

240 240 3.3 amps 1750lug 792 240 187 1.4 amps 1150Lux 336 Overall V.A. reduction of approx 59% Although the V.A. values given in the table above are given without power factor correction, they indicate that considerable power savings can be achieved by means of the present invention.

Claims (12)

1. Control circuitry for a fluorescent light, the circuitry being adapted to cause a first voltage to be applied to the fluorescent light for a predetermined time sufficient to allow the light to reach a stable operating state, whereafter a second voltage, lower than the first voltage, is applied to the light.

2. Control circuitry as claimed in claim 1, wherein the predetermined time is in the range 3 to 10 minutes.

3. Control circuitry as claimed in claim 2, wherein the predetermined time is in the range 4 to 6 minutes.

4. Control circuitry as claimed in any preceding claim, wherein the first voltage is the mains supply voltage, and the second voltage is in the range of 60% to 80% of the first voltage.

5. Control circuitry as claimed in any preceding claim, wherein the value of the second voltage may be selected from two or more possible values, so that the intensity of illumination can be varied.

6. Control circuitry as claimed in any preceding claim, comprising a timer circuit controlling the operation of one or more relays for switching the output of the circuitry between the first voltage and the, or one selected, second voltage.

7. Control circuitry as claimed in any preceding claim, wherein the second voltage is estab lished by means of a potentiometer.

8. A refrigerated cabinet comprising at least one fluorescent light disposed within the cabinet for illuminating the interior of the cabinet, the light being controlled by control circuitry as claimed in any one of claims 1 to 7.

9. A refrigerated cabinet as claimed in claim 8, where the or each fluorescent light is shielded against air turbulence within the cabinet.

10. A refrigeration cabinet as claimed in claim 9, wherein the shielding comprises a strip of perspex or other transparent material disposed adjacent the tube.

11. A refrigeration cabinet substantially as herein described with reference to Fig. 1 of the accompanying drawings.

12. Control circuitry substantially as herein described with reference to Fig. 2 of the accompanying drawings.