GB2060852A - Decorative multi-coloured lamps - Google Patents

Abstract

A decorative electric lamp which can give a randomly varying light output both of intensity and colour comprises three electric lamps 10, 12, 14 each emitting light of a different colour. The energising current for each lamp is controlled by a series transistor 22, 24, 26 and an oscillating circuit 28, 30, 32 controls the conductivity of its respective transistor. The period of oscillation of each oscillation circuit is randomly different from the other two and each circuit includes a silicon controlled rectifier 44, a zener diode 48 and a diac 50. <IMAGE>

Description

SPECIFICATION Decorative lamps This invention relates to an electric lamp arranged for decorative purposes to emit a continuously varying light output.

Decorative electrical lamps can be provided with a light output, the colour of which does vary with time by rotating, by means of an electric motor, a disc carrying various colour filters in the path of the light output. The use of such a motor both adds to the cost of the item and tends to limit the variation in colour of the light output to a relatively short-term, regularjy repeating pattern.

According to the invention, there is provided a decorative electric lamp comprising three electric bulbs each arranged to emit light to a different colour from the other two, the current through each bulb being controlled by means of a transistor in series with each individual bulb, and an oscillating circuit associated with each transistor to control the conductivity of the transistor, the period of oscillation of each oscillating circuit being randomly different from the other two oscillating circuits so that the light output from the lamp varies.

In this way, an entirely random pattern of light output colour can be given since the light output from each bulb can be arranged to vary in a random fashion dependent upon the frequency of oscillation of its associated oscillator and the frequency of oscillation of the three different oscillators can be chosen so as to be different. Additionally, random changes with time inevitably occur in each oscillating circuit unless it is carefully stabilized and so by allowing the rate of oscillation of each oscillator to change with time to a small extent, an almost infinite number of changes will occur before repetition.

The decorative lamp of the invention will, therefore, emit any coloured light output ranging from almost zero light output from all three bulbs to an approximately white light output at the moment when all three bulbs are fully energised. At other times, one or two of the bulbs may be giving high output and so since the bulbs give a light output corresponding to the three primary colours, the additive result of this can be any colour from the spectrum and in addition the intensity of the light will also change with time independently of the change in colour.

The three colours of light emitted by the bulbs are red, blue and green.

Preferably, the output of light from the three bulbs is passed through a diffuser but this is not essential.

The oscillating circuit can include a capacitor which alternately charges and discharges and which is connected to the base of the power transistor. The capacitor is arranged to charge and discharge through resistors and so the rate of charging and discharging can be chosen by a selection of the value of these resistors. The discharging of the capacitor can be controlled by an electronic switch such as an SCR and the gate of this can be opened and closed through a triggering circuit. The latter could, for example, include a diac or other device which breaks down at a preselected peak voltage, this device being energised from the same AC source as the remainder of the circuit.

A circuit for a decorative lamp according to the invention will now be described, by way of example, with reference to the accompanying drawing which shows a circuit diagram of the lamp.

The lamp includes three bulbs 10, 1 2 and 14 whose glass envelopes are coloured or covered by means of a filter so that the light output from the bulbs is respectively red, blue and green. The bulbs are supported by a common housing and enclosed within a suitable shade but for simplicity, these parts are not shown in the drawing.

Each bulb 1 2 and 1 4 is supplied from its own respective full-wave rectifying bridge 16, 18 and 20 and is in series with its own power transistor 22, 24 and 26 respectively. In this way, the current through each bulb and therefore the amount of light output of that particular coloured light is dependent upon the conductivity of the respective power transistor and this conductivity is varied by varying the voltage applied to the base of the transistor as described below.

The three rectifier bridges 1 6 to 20 are conventional and are supplied in parallel from the secondary of a transformer 30 whose primary is supplied with AC mains electricity.

These rectifying bridges are entirely conventional and are not believed to require any further explanation.

Associated with the power transistors 22, 24 and 26 are oscillating circuits 28, 30 and 32 and whilst each oscillating circuit is identical in general construction and operation, precise values of the components of the oscillating circuit vary from circuit to circuit so that the period of oscillation of each circuit differs either because of a choice of differing value components or because the values of the components differ within the tolerances allowed. For simplicity, only a single oscillating circuit, circuit 28 associated with the power transistor 22 will be described in detail.

The oscillating circuit 28 includes a charging resistor 40 supplied with the same voltage as the collector of the power transistor and through which, in series with the lamp bulb 10 and the base to emitter resistance of the power transistor 22, a capacitor 42 linked to the base of the power transistor is charged.

Parallel with the capacitor 42 is a silicon controlled rectifier (SCR) 44 in series with a discharging resistor 46. The triggering of the gate of the silicon control rectifier is controlled by means of a zener diode 48 in series with a diac 50 and a current-limiting resistor 52, the diode being connected to a further terminal B on the secondary of the transformer 30. In cases where a diac is available which matches the voltages of the overall system, the zener diode 48 can be omitted.

In operation, therefore, the voltage on the base of the power transistor 22 and therefore the current passing through the bulb 10 is controlled by the progressive charging and discharging of the capacitor 42.

Initially, the gate on the SCR 44 is open so that the SCR is non-conductive or not freely conductive. As a result, the capacitor 42 becomes gradually and progressively charged through the resistor 40 in series with the lamp bulb 10 and the base to emitter resistance of the transistor 22 and so tha transistor 22 progressively becomes less conductive. Therefore, the current through the bulb 10 decreases from an initial high value.

As the cathode of the SCR becomes more and more negative in potential by the charging of the capacitor 42 so also does the gate of the SCR. Thus when the terminal B is at its positive cycle, there is an instantaneous potential difference between the gate of the SCR and terminal B with terminal B being at a more positive potential, and this instantaneous potential difference increases in value with the charging of the capacitor. At a certain value of this instantaneous potential, the zener diode 48 and diac 50 break down and a triggering voltage, together with a triggering current, reaches the gate of the SCR and so the SCR becomes triggered or in other words, conductive. The resistor 52 limits the triggering current to a safe level and so protects the SCR, the diac and the zener diode from too high a current.Once the SCR is triggered, the capacitor begins to discharge and so the gate potential of the SCR rises. Accordingly, the instantaneous potential difference across terminal B and the gate drops abruptly and can no longer keep the disc and zener diode in breakdown condition. As the capacitor discharges, the transistor 22 progressively becomes more conducting and so increases the current through the bulb 10.

Once the capacitor 42 has discharged sufficiently, the gate on the SCR 44 will again open and so the capacitor 42 will begin to charge again through the resistor 40 in series with the bulb 10 and the base to emitter resistance of the transistor 22 so starting the cycle again.

In this way, the circuit 28 will oscillate and so the current through the bulb 10 will fluctuate at a rate depending upon the rate of oscillation of the oscillating circuit 28.

Inter alia, the values of the resistors 40 and 46 determine the rate at which the capacitor 42 will charge and discharge and so on the rate at which the brightness of the bulb 10 will fluctuate. The values of these and other components in the oscillating circuits associated with each bulb 10, 1 2 or 1 4 are chosen so that the rate of fluctuation of brightness of each bulb varies at a different rate. This can be achieved by choosing different values for the components of the oscillating circuit but equally, differences in the rate will inherently occur because of different values for each component within its tolerance and as a result, the differences in the rate of oscillation will be random.Also, the rate of oscillation will be dependent upon the resistance of the bulbs 10 and 14 and so changing in these bulbs or progressive changes with time of usage will vary the rate of oscillation. The circuits 28 to 32 also affect one another and so the relative rates of oscillation. Further, random changes will occur with time caused, for example, by warming of the various components. It will be noted that the circuit shown in the drawing is not stabilized by the use of various additional electronic circuitry and so these random changes can occur.

The relative brightness of the three lamps 10, 1 2 and 14 will, therefore, vary in a random and non-repeating fashion so giving a light output whose brightness and colour vary in a random fashion. Also the charging and discharging cycles of the capacitor 42 will differ which will add a further degree of variation to the appearance of the light output. In general, the charging cycle of the capacitor corresponding to the dimming of a bulb, will be slower than the discharging cycle. With different design of oscillating circuits, however, this can be altered.

As will be seen, the decorative lamp of the invention can give a random light brightness and colour output in a simple fashion which does not require the use of motors but uses instead simple electronic circuitry. The rates of oscillation of the various circuits 28 can be chosen within wide ranges but preferably, the rate of oscillation is relatively slow so that disturbing sudden changes in colour and brightness do not occur. Thus, for example, the rate of oscillation could vary from 1 cycle per 1 5 seconds to 1 cycle per 35 seconds.

Claims (5)

1. A decorative electric lamp comprising three electric bulbs each arranged to emit light of a different colour from the other two, the current through each bulb being controlled by means of a transistor in series with each individual bulb, and an oscillating circuit associated with each transistor to control the conductivity of the transistor, the period of oscillation of each oscillating circuit being randomly different from the other two oscillating circuits so that the light output from the lamp varies.

2. A decorative electric lamp as claimed in Claim 1 in which the oscillating circuit in clues a capacitor which is alternately charged and discharged, the state of charge of the capacitor providing a voltage which controls the conductivity of the associated transistor.

3. A decorative electric lamp as claimed in Claim 2 in which the capacitor is continuously charged through a resistor from a supply and its discharge occurs through another resistor in series with an electronic switch, the gate of which is opened and closed by a triggering circuit.

4. A decorative electric lamp as claimed in Claim 3 in which the triggering circuit includes a diac or other device which breaks down and becomes conducting at a preselected peak voltage, whereby this voltage becomes reached or exceeded as the capacitor becomes charged to a preselected extent.

5. A decorative electric lamp substantially as herein described with reference to the accompanying drawing.