GB2137828A

GB2137828A - Strobe Lighting Arrangement

Info

Publication number: GB2137828A
Application number: GB08308595A
Authority: GB
Inventors: Paul Francis Mardon; Kenneth Sewell
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-03-29
Filing date: 1983-03-29
Publication date: 1984-10-10
Also published as: GB8308595D0; GB2137828B

Abstract

A strobe lamp 30 is supplied with power from a power supply circuit in which the power supply circuit operates so as to maintain approximately constant power consumption independent of flash rate within a predetermined working flash rate range. In this way the rating of the lamp is not exceeded at higher flash rates and greater brilliance is available at lower flash rates. The lighting effect is enhanced at low flash rates where previously four joules per flash has been common and now a theoretical twenty-five joules per flash can be achieved. The lamp discharge voltage varies from 200 volts at 25 flashes per second to 680 volts at one flash per second and the limitation of energy per flash is achieved by selecting the values of two capacitors, one 44 connected in series with the discharge lamp 30 and the other 38,40 in parallel therewith in a voltage doubler circuit. Typical values are 12 mu F and 70 mu F for the series and parallel capacitor respectively. Power consumption is maintained constant within +/-15% over a range from 2.5 to 20 flashes per second. With a switch 12 closed, the flash rate is varied by an adjustable resistor 24 in a lamp firing circuit 14 with switch 12 open the flash rate is controlled by an input signal supplied to a jack 32 and derived from a musical rhythm. <IMAGE>

Description

SPECIFICATION Improvements in Strobe Lighting Arrangements Field of Invention This invention relates to a strobe lighting arrangement, in particular used to create special lighting effects by means of a flashing light, for example at discos and dances and on the stage.

Background to the Invention Conventional strobe lighting arrangements include a discharge lamp repetitively fired by a control circuit to produce flashes of light at a desired rate. The rate of flashing is determined by either a setting of the control circuit or by an input signal to the- control circuit. This input signal may for example be derived from a pulse generator which may itself be partially controlled from music, such as the rhythm produced on drums. The usual flash rate desired is of the order of two to twenty-five flashes per second; a rhythm derived input signal may automatically vary the flash rate approximately within this range and/or the control circuit may incorporate a variable component for adjusting or varying the flash rate generally in said range.

In either case, the conventional control circuit operates to produce a flash of uniform intensity regardless of the flash rate. In a typical case a reasonabie light level at low flash rates is achieved by delivering four joules per flash, giving .8 watt power consumption at two flashes per second. If the discharge lamp has 50 watt rating then the maximum flash rate permissible is a mere twelve and a half flashes per second.

It is an object of the present invention to provide a device wherein the maximum flash rate is not so limited by the power rating of the lamp.

The Invention According to the present invention there is provided a strobe lighting arrangement comprising a flash control circuit and power supply circuit wherein the power supply circuit for the discharge lamp operates so as-to maintain approximately constant power consumption independently of flash rate within a predetermined working flash rate range, so that the rating of the lamp is not exceeded in higher flash rates and greater brilliance is available at lower flash rates.

The invention thus has the advantage that an enhanced lighting effect is achieved at low flash rates where previously four joules per flash will have been common and now a theoretical twenty-five joules per flash (for a 50 watt dissipation) could be achieved although in practice, power supply limitations may limit the power available at the lower flash rates. Thus, for example, at two flashes per second the energy available may be restricted to fifteen joules per flash.

In a preferred arrangement, the power consumption is maintained within +15% of a constant value over a predetermined working range from 2.5 flashes per second to 20 flashes per second. Both below and above this working range, the power consumption is reduced. The constant value may conveniently be about 45 watts. At one flash per second power consumption may be reduced to about 20 watts and at 30 flashes per second be reduced to about 30 watts.

In one embodiment of the invention the strobe power supply circuit employs a voltage doubler comprising a first capacitor 44 and a first diode 50 in series with the discharge lamp 30 and a second diode connected between the junction of the first capacitor and diode and the remote end of the lamp.

The second capacitor is connected in parallel with the discharge lamp. The limitation of energy per flash is achieved by selecting the values of the two capacitors so as to produce substantially constant power dissipation in the working range.

In the past, the aim of obtaining constant joules per flash has necessitated maintaining the voltage across the flash capacitors.substantially constant throughout the working range. In the circuit according to the invention a variable lamp discharge voltage, say from about 200 volts at 25 flashes per second to about 680 volts at one flash per second is developed.

In one circuit in-accordance with the invention the first capacitor has a value of 12 ,uF and the second capacitor a value of 70 yF.

Preferably metallised polypropylene capacitors are utilised in the control circuit of the invention.

Description of Embodiment In the accompanying drawings: Figure 1 illustrates a strobe control circuit and power supply circuit in accordance with the invention; Figure 2 illustrates the power supply circuit alone of Figure 1, and Figure 3 depicts curves showing the power characteristics of the circuit of Figure 1.

The circuit of Figure 1 is a strobe control and power supply circuit in which L and N designate mains supply input leads to the circuit, wherein a double-pole switch 10 is provided. When the ganged switch 12 is closed, the circuit 14 including electrolytic capacitor 1 6 is energised. Transistors 18, 20 are operated repetitively to fire the thyristor 22. The capacitor 1 7 charges up to switch on the transistors 18, 20, when a given threshold is attained. The capacitor discharges eventually on conduction of 1 8 and 20 to switch off the transistors. The charging time and therefore flash rate is adjustable by the setting of the variable resistor 24.

The thyristor 22, when fired, allows discharge of a capacitor 26 through one coil of a transformer 28 having a 1:35 ratio, whereby a firing voltage of about 9000 V is obtained for firing a 50 watt discharge lamp 30.

When the switch 1 2 is open, the thyristor 22 can instead be repetitively fired by an input through a jack point 32, which leads to an opto-isolator 34 and transistor 36. The jack input may, for example, receive from a remote point a pulsating signal derived from drum beats or similar musical rhythm.

The lamp discharge voltage which determines the joules per flash (calculated by -21 C. V2) -is developed across capacitors 38, 40.

The power supply comprises 10 R short circuit protecting resistor 42, 12 yF capacitor 44, diodes 46, 48 and 50, 52, in addition to capacitors 38, 40 each having a value of 35 ,us.

The effect of this voltage doubler is to cause a variable discharge voltage to be developed across the discharge lamp, dependently on the flash rate. The variation is such that to a first approximation, - the same power is consumed at all flash rates within the working range, say 2 to 25 flashes per second, meaning that the joules per flash increase from the top flash rate to the bottom flash rate.

The following table exemplifies the circuit according to the invention for flash rates of from 25 flashes to one flash per second, and shows that the lamp discharge voltage varies from about 200 V up.

to 680V (double the mains peak).

Mains Cycles Flash Rate Volts J/F2 P2 2 25 199 1.39 35 3 162/3 269 2.53 42 4 121/2 330 3.81 48 5 10 381 5.08 51 6 81/3 425 6.31 52.6 7 7.1 462 7.47 53 8 6.25 492 8.54 53 10 5 544 10.36 52 15 31/3 619 13.41 44.7 20 2.5 652 14.9 37 30 1 2/3 674 15.9 26.5 40 1 1/4 679 16.1 20.2 50 1 680 16.2 16.2 Power consumption varies from 1 6.2 watts at one flash.per second up to 53 watts at around 7 to 8 flashes per second, but in fact lies within + 1 5% of 45 watts'for the range 2 to 20 flashes per second, in contrast to the power consumption variation of 8 to 80 watts in the same range using a conventional circuit such as previously described for delivering four joules per flash.

Joules per flash varies from 1.39 at 25 flashes per second to 16.2 at one flash per second, in contrast to the constant intensity flash produced (typicaily four joules per flash) at all permissible flash rates in a conventional arrangement.

Reverting to power consumption, it is especially to be noted that this reduces both below and above the working range of 2 to 20 flashes per second.

The differences between the circuit of Figures 1 and 2 and a conventional strobe control circuit are demonstrated in Figure 3, wherein power P, and joules/flash J/F1 refer to a conventional circuit and P2 and J/F2 refer to the circuit of this invention. The abscisse for these curves is marked in flashes per second.

Various modifications of the above-described arrangement are possible within the scope of the invention as hereinbefore defined.

Claims

CLAIMS (Filed on 18 Oct 83)

1.-A strobe lighting arrangement comprising a flash control circuit and a power supply circuit wherein the power supply circuit for the discharge lamp operates so as to maintain approximately constant power consumption independently of flash rate within a predetermined working flash rate range, so that the rating of the lamp is not exceeded in higher flash rates and greater brilliance is available in low flash rates.

2. A strobe lighting arrangement as claimed in Claim 1 wherein the power consumption is maintained within plus or minus 15% of a constant value over a predetermined working range from 2.5 flashes per second to 20 flashes per second.

3. A strobe lighting arrangement as claimed in Claim 1 which incorporates a voltage doubler comprising a first capacitor and a first diode in series with a discharge lamp and a second diode connected between the junction of the first capacitor and diode and the remote end of the lamp and a second capacitor is connected in parallel with the discharge lamp and energy limitation per flash is achieved by suitable selection of the values of the two capacitors so as to produce substantially constant power dissipation in the working range.

4. A strobe lighting arrangement as claimed in Claim 1,2 or 3 wherein the discharge voltage for the lamp varies from approximately 200 volts at 25 flashes per second to approximately 680 volts at one flash per second.

5. A strobe lighting arrangement as claimed in either of the preceding Claims wherein the first capacitor has a value of 12,us and the second capacitor a value of 70,us.

6. A strobe lighting arrangement as claimed in any of the preceding three Claims wherein the capacitors are metallised polypropylene capacitors.

7. A strobe lighting circuit and power supply circuit constructed, arranged and adapted to operate substantially as herein described with reference to and is illustrated in the accompanying drawings.