US3857064A

US3857064A - Automatic control of light flash pulses

Info

Publication number: US3857064A
Application number: US00244279A
Authority: US
Inventors: Z Vital; J Orban
Original assignee: Ponder & Best
Current assignee: Ponder & Best; Ponder & Best Inc us
Priority date: 1968-02-13
Filing date: 1972-04-14
Publication date: 1974-12-24
Anticipated expiration: 1991-12-24
Also published as: JPS5123907B1; DE1966983A1; JPS5633821B1; FR2001833A1; GB1267234A; DE1907059A1; JPS5223260B1; US3818266A; DE1907059B2; DE1966984A1

Abstract

A device for controlling the termination of light emission by a flash device including means for detecting the light reflected from the subject being illuminated by the flash, integrating means connected to the detecting means for providing a flash termination signal when the total amount of light received by the detecting means reaches a predetermined value, and flash termination means connected to the integrating device and to the flash device for terminating the delivery of electrical energy to the flash device when the signal from the integrating device reaches its predetermined value. The flash termination device is preferably constituted by a novel gas-filled, arc-producing element having identical, unpolarized electrodes and an internal or external triggering electrode.

Description

United States Patent Vital et al.

[ 1 Dec. 24, 1974 AUTOMATIC CONTROL OF LIGHT FLASH PULSES [75] Inventors: Zoltan Vital, Uccle; Jean Orban,

Clabecq, both of Belgium [73] Assignee: Ponder & Best, Inc., Los Angeles,

Calif.

[22] Filed: Apr. 14, 1972 [21] Appl. No.: 244,279

' Related U.S. Application Data [63] Continuation of Ser. No. 799,554, Feb. 13, 1969,

abandoned.

[30] Foreign Application Priority Data Feb. 13, 1968 Belgium 54471 Nov. 21, 1968 Belgium 66425 Dec. 27, 1968 Belgium 68017 Jan. 20, 1969 Belgium 68982 [52] U.S. Cl. 315/241 P, 315/151, 315/159, 315/241 R [51] Int. Cl. H05b 37/02 [58] Field of Search 315/149, 151,159,241 P, 315/241 R; 307/252 B; 323/22 SC [56] References Cited UNITED STATES PATENTS 3,525,033 8/1970 Greenberg et al. H 323/22 SC FIRING VOLTAGE SUPPLY 3,591,829 7/1971 Murata et al. 315/151 Primary Examiner-Harman Karl Saalbach Assistant ExaminerLawrence J. Dahl Attorney, Agent, or FirmSpencer & Kaye [57] ABSTRACT A device for controlling the termination of light emission by a flash device including means for detecting the light reflected from the subject being illuminated by the flash, integrating means connected to the detecting means for providing a flash termination signal when the total amount of light received by the detecting means reaches a predetermined value, and flash termination means connected to the integrating device and to the flash device for terminating the delivery of electrical energy to the flash device when the signal from the integrating device reaches its predetermined value. The flash termination device is preferably constituted by a novel gas-filled, arc-producing element having identical, unpolarized electrodes and an internal or external triggering electrode.

VOLTMETER I08? H QE INTEGRATOR suaazcr Patented Deg. 24, 1974 3,857,064

9 Sheets-Sheet l VOLTM ETER I08 52E25;

g I INTEGRATOR W SUBJECT J I05 FIRING I m VOLTAGE cmculn I SUPPLY I I 7r @1 I 200 205 Z04 E LECTRO N c s WITCH JZ Fig. J

10/ J04 J07 J11 J08 m/ VENTORS Zolton Vital 8 Jean Orbon A TTORNEYS Patented Dec. 24, 1974 9 Sheets-Sheet 2 COMPENSATING INVENTORS ATTORNEYS CAMERA Ell- SYNCHRONIZING CONTACTS APERTURE DISC Zolton Vitul8 Jean Orbcm Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet Z 7v VE N TORS Zolton vitala Jean Orbon ATTORNEYS Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet 4 Fig. 10

m fiv'vslvrofi's Zoltan Vital 8 Jean Orbun ay mi ATTO NEYS Patented Dec. 24, 1974 9 Sheets-Sheet 5 Fig. [3

Fig. I4

. INVENTORS Zolton Vital 8 Jean Orban BY m am 5 7 67 2 A TTORNEYS Patented Dec. 24, 1974 9 Sheets-Sheet 6 INVENTORS Zoltcm Vitol 8 Jean Orbon AT TORN E YS Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet 7 PHOTO- EMISSION FIBER LENS MATERIAL F ig. I9

INVENTORS Zdl ton Vital 8 Jean Orbon ATTORNEYS Patented Dec. 24, 1.974 3,857,064

9 Sheets-Sheet 8 IN VE N TORS Zolton Vital 8 J an n O rbo n ATTORNEYS Patented Dec. 24, 1974 3,857,064

9 Sheets-Sheet 9 Fig. I8

C9 w i H may INVENTORS Zolton Vitalfi Jean Orbon ATTORNEYS AUTOMATIC CONTROL OF LIGHT FLASH PULSES CROSS REFERENCE TO RELATED APPLICATION This application is a continuation of application Ser. No. 799,554, filed Feb. 13th, 1969 now abandoned.

BACKGROUND OF THE INVENTION The invention concerns a device, circuit and method for controlling the impulses generated by the discharge of a capacitor placed either in series or in parallel with the load and, in the case of a parallel connection, having no more than one electronic switch. The invention further concerns a novel switching tube for use as such switch and having other uses and equipped with at least one important further device or circuit.

The invention is intended above all for application to electronic flashes, stroboscopes and lasers.

Such devices are now only known for effecting such control in an automatic manner and with the capacitor causing the impulse to bypass the load. Apparatus of such kind is disclosed in U.S. Pat. No. 3,033,988 and is composed of a device which controls the light of a photographic enlarger and in which a gas-discharge switching triode with an external firing electrode or a mercury tube is provided as a second switch, always with an impedance of about O.l ohm. Concerning the light sensor of this patent, U.S. Pat. No. 3,350,604 states, at column 3, lines 27-32: In order to achieve the high photocell dark impedance with the required high light sensitivity, the light sensitive element must be a photomultiplier tube. Such tubes require a rather complex power supply. This results in a package which is sufficiently bulky as to preclude its use in portable, camera mounted flash equipment. Another known device of the same kind is disclosed in U.S. Pat. No. 3,350,604, which is essentially based on the disclosure of U.S. Pat. No. 3,033,988, and represents a modification thereof in that this device makes use of a nonreactive light integrator, i.e., one without a capacitor, and the patent states that the use of this is more advantageous than that of the integrator of U.S. Pat. No. 3,033,988.

These'known devices, which can only operate in an automatic manner, i.e., by being coupled permanently to a sensor, always have two or more switches. The switch of the second U.S. Pat. No. (3,350,604) is a xenon gas-filled discharge tube, a variant of the wellknown xenon gasfilled photoflash tube, equipped with an internal firing electrode and having a pressure of about I mm Hg. The internal resistance of this tube is mentioned as being 0.1 ohm.

SUMMARY OF THE INVENTION According to the present invention, an improved control is achieved by a control device serving to arrest the discharge of a capacitor, and thus extinguish the flash tube.

A modified embodiment of the invention involves a control device which is used only to extinguish the flash tube. In this case, we use only one electronic switch or a gas-filled switching tube of new design, which relies on an arc operation and is thus different from the gas discharge tubes of the two U.S. patents discussed above, and which consumes the residual electrical energy of the capacitor, not used by the flashtube, the switch then being in a bypass circuit. In addition, we use at least one important complementary device or circuit, such as a special electronic gate, a device for the regulation of the sensitivity, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram of a control circuit according to the invention.

FIG. 2 is a view similar to that of FIG. 1 of another form of construction of a control device according to the invention.

FIG. 3 is a view similar to that of FIG. 1 of a further control device according to the invention.

FIG. 4 is a view similar to that of FIG. 1 of still another control device according to the invention.

FIG. 5 is a schematic circuit diagram of a modified type of control circuit according to the invention.

. other embodiment of the modified type of control circuit according to the invention.

FIG. 9 is a view similar to that of FIG. 5 of a still further embodiment of the modified type of control circuit according to the invention.

FIG. 10 is a view similar to that of FIG. 5 of yet another embodiment of the modified type of control circuit according to the invention.

FIG. 1 l is a view similar to that of FIG. 5 of yet a further embodiment of the modified type of control circuit according to the invention.

FIG. 12 is a view similar to that of FIG. 5 of a further embodiment of the modified type of control device according to the invention.

FIG. 13 is a view similar to that of FIG. 5 of another embodiment of the modified type of control device according to the invention.

FIG. 14 is a view similar to that of FIG. 5 of a further embodiment of the modified type of control device according to the invention.

FIG. 15 is a view similar to that of FIG. 5 of a further I FIG. 20 is an elevational view of one embodiment of a novel arc-operated switch according to the invention.

FIG. 20a is a cross-sectional view of the embodiment of FIG. 20.

FIG. 21 is a view similar to that of FIG. 20 of another embodiment of the switch according to the invention.

FIG. 21a is a cross-sectional view of the embodiment of FIG. 21.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention concerns devices and circuits for controlling impulses generated by the discharge of a capacitor. These impulses are controlled by components placed in series and/or parallel withthe load and including an integrator which receives the energy of the impulses. This control device may be operated in a manual and/or an automatic manner. All these devices are combined preferably with several other devices and circuits. The invention is especially related to electronic photoflashes,stroboscopes,.lasers and the like, the reflected light of which is to be received by a light sensor whose output signal is to be integrated. When the light sensor has received a predetermined quantity of light, a threshold amplifier consisting of a unijunction transistor, a four-layer diode or any other suitable component and placed after the integrator generates impulses which control one or several semiconductor switches and/or one or several gas-filled tubes and/or one or several lightning arresters preferably of the gasfilled type, and/or, most particularly, one or several gas-filled arc arresters of special construction to be described later in a detailed manner, and/or other similar components.

These components control the electrical supply of a flash tube, the impedance of which is higher than that of the switch, with or without arresting the discharge of the photoflash capacitor. Another essential element of this invention is the above-mentioned new type of arc arrester component of the gas-filled type, having an impedance of about 0.0] ohm when in its conduction state, fitted with at least two electrodes, preferably un polarized and even of identical size, and internally or externally completed with a firing electrode. This new type of gas-filled switching tube differs from other gasfilled switching tubes above all because it functions on the basis of an arc and not as a gas-discharge tube of the type used in the prior art. The tube according to the present invention has the following advantages over all other gas-filled switching tubes, such as those of the two above-cited U.S. patents: lower impedance; larger range of current intensities and voltages; higher resistance to overloads; easier firing, and this over a more extended range; lower light emission; possibility of utilization at faster switching rates; increased ruggedness; extended lifetime, smaller sizes; and lower cost.

Furthermore, this new component is suitable for use in fields where thyratrons and thyristors are presently used or where no convenient component is available.

We remark that our control device, when using only one electronic switch or the gas-filled, arc-operation tube according to the invention is considerably smaller than all other similar devices, which is of the greates importance in the case of portable devices.

We describe the supplementary devices and circuits intended to be combined with the control device.

The control device may be completed by one or scvcral electronic gates. The function of the electronic gate is to conduct current from the electric supply of the control device only during the period of the flash discharge. The supply current is initiated by the discharge of a capacitor. associated with the electronic gate. This capacitor was previously charged by the photoflash discharge capacitor through a resistive, inductive, semiconductor, or other element. The supply voltage is controlled by a Zener diode, a gas-filled tube, a capacitor, a resistance, or another element.

It is the electronic gate which starts and maintains this control device for the duration of each flash of the photoflash and which sets the control device back to its starting point right after the flash is terminated. Thus, it is not possible for the control device to be actuated by any other source of light.

On the other hand, the control device may be completed with a device that regulates its own sensitivity, namely, by an adjustable optical device, such as a diaphragm, a set of filters, or others, placed in front of the light sensor of the control device, or by an adjustable electric or electronic device, such as fixed and/or variable capacitances, resistances and inductances.

These controls can be operated manually or else by coupling to a part or accessory of the camera, such as to the diaphragm, the film cassette, e.g. a coded Kodapak cassette, etc. Of course, in the case of a control coupled to the camera, both apparatuses should be constructed together.

The regulating components, being designed to be manipulated by the user, are completed with scales graduated in film sensitivities and/or in diaphragm apertures. The selected positions could be ratcheted or locked. The components to be manipulated and the scales are preferably interchangeable and reversible. This same device could be completed by a focal lengthaperture calculator. This same device and its scales can be lighted.

Another mode operation consists of controlling the quantity of light produced by the flash tube by a manual regulation of the control device of the integrator, without intervention by'a light sensor, i.e., without taking into account the quantity of reflected light, based on the camera-to-subject distance, the film sensitivity, etc. In this case, the lightsensor of the control device is replaced by at least one adjustable component, e.g. the setting element of the threshold amplifier of the integrator, etc. The controls of this device may be graduated in distance, flash-duration, guide-numbers, etc.

Another control function is a determination of whether the operation of the control device was completed or not. This control consists of a suitable electric or electronic circuit or else a light sensor, such as a photosensitive element, etc., or a conductor of visible or nonvisible light, such as fiber optics, transparent material, etc., or a heat conductor, i.e., responsive to infrared radiation, used in conjunction with a gas-filled switching tube, or'with any other component of the control device havingthe kind of emission as described above.

The control device can be completed with a circuit having an electric or electronic measuring instrument which allows the light integrator to function as a photometer, a chronometer, etc., and thus to execute different measurements, such as the amount of light reflected, the duration of the flash, etc.

A photoflash equipped with a control device may be advantageously completed with a compensation device, e.g. an induction coil and/or a suitable circuit, connected in series with the flash tube to modify the discharge impulses to the flash tube, for instance to slow down the discharge of the capacitor, which means to reduce the rate of increase of the current density of the capacitor discharge. FIG. 1 shows the circuit of an electronic photoflash equipped with a control device having only one switch whose purpose is to arrest the capacitor discharge when a predetermined amount of light has been produced.

The arrangement of such a unit is as follows:

An energy storage capacitor 100 is charged through a voltage source 101. A flash tube 102 of the usual type is connected to the capacitor terminals through a switch 103 which is preferably a gate-turn-out thyristor or thyratron, etc., provided, if necessary, with suitable supplementary circuitry. A light sensor 104, composed of a photodiode, phototransistor, photoresistance, or other, is connected to an integrating circuit 105 of any well-known type. A firing circuit 106 triggers the firing of the flash tube 102. This device works as follows:

The capacitor 100 having been charged by the source 101, the ionization of the flash tube 102 is induced by the action of the firing circuit 106. The light sensor 104 supplying an instantaneous current proportional to the illumination on subject 107, to the integrating circuit 105, the latter, when the total amount of light received by the light sensor 104 reaches a predetermined value, causes a circuit to swing," thus supplying an impulse to the switch 103 which then interrupts the discharge of the capacitor 100. A

Thus, the light emission of the flash tube is arrested after producing the requisite amount of light, without any energy being withdrawn from the capacitor other than that used for producing the light, and possibly for commutating the circuit.

The arrangement of FIG. 1 may be completed in the following manner: by connecting a voltmeter 108 to the terminals of the integrator circuit 105, which is designed for such a connection, an integrating photometer, or chronometer, can be produced, which device has scales in different measuring units.

Another variant is illustrated in FIG. 2 in which we describe a control device connected both in series and parallel with the load and combined with a compensating device, capable of also being used with the preceding embodiment, constituted by an induction coil.

The discharge capacitor 200 is charged through the voltage source 201. The flash tube 202 is connected to the terminals of the capacitor 200 through the intermediary of the induction coil 203. A thyratron 204 is connected in parallel with the flash tube 202. A light sensor 205 is coupled to the integrating circuit 206, receives reflected light from subject 209 and controls the firing electrode 207 of the thyratron 204. A firing circuit 208 acts to fire the flash tube 202. Meter 210 is connected to circuit 206.

The operation of the circuit of FIG. 2 differs from that of FIG. 1 as follows:

After reaching the predetermined signal value, the circuit of the integrator 206 triggers the firing electrode 207 of the thyratron 204 in parallel with the flash tube 202. The induction coil 203 allows for a short period during which the thyratron is practically in shortcircuit. Consequently, the flash tube 202 has enough time to deionize, and hence to become extinguished.

A modification is illustrated in FIG. 3. This control device is combined with both an electronic gate and an optical device of regulation of the sensitivity.

The control device consists of an electronic device 30 which is identical with the device 50 of FIG. 5, of

the-photoflash unit 31 and of an electronic switch 32.

In this device, a light sensor 301 generates a current proportional to the reflected light from the subject. This current is integrated by a capacitor 302 to give a voltage proportional to the amount of the reflected light. This voltage is applied to a unijunction transistor 304 or to a four-layer diode or to some other element or device which would serve as suitable substitute, which develops a positive impulse in the resistance 305 as soon as the threshold swing orswitching level, of this component 304 has been reached.

This impulse is conducted by the capacitor 306 to open a semiconductor switch, or other gate element, 308 by means of its firing circuit which controls the electronic switch 32 so as to terminate the capacitor discharge and thereby extinguish the flash tube of the photoflash 31. I

As soon as the cycle is ended, the voltage across a resistance 303 sets the system back to its initial condition. A resistance 307 prevents a premature opening of the semiconductor switch 308. The unit 31 contains the elements of the photoflash which are not individually referenced. The electronic device 30 contains as its principal element a semiconductor switch, such as a thyristor (SCR), or else a gas-filled switching tube, preferably of the arc arrester type or a special arc arrester, or another suitable component.

An improvement of the flash control device consists in equipping this device with a voltage applying circuit for the reflected light sensor circuit.

FIG. 3 also illustrates this circuit arrangement. When the flash tube is fired, the voltage at the flash tube terminals decreases sharply. This results in a current in the circuit of the capacitor 309, the resistance 310 and the diode 311. A voltage equal to that across the zener diode appears at the terminals of the light sensor circuit so as to place it in operation. The current intensity depends on the resistance value of resistor 310. The period voltage is applied to the light sensor circuit is on the value of the capacitor 309.

The regulation of the sensitivity of the control device is effected by the user with the help of an adjustable optical device 315 composed of a diaphragm, a set of filters, or others, placed in front of the light sensor301 of the control device.

A further explanation is given with reference to FIG. 4 which shows a light control device for the flash of an electronic photoflash, consisting of the electronic device 40, which is similar to the device 30 of FIG. 3 and the device 50 of FIG. 5 and which is therefore only partially shown, of the photoflash 41, which is similar to the device 31, and of an electronic switch 42, which is similar to the device 32, connected in series with the flash tube circuit.

This device and its operation are essentially identical to those described and illustrated previously, namely:

The thyristor 421, which is tired upon closing of the camera synchronization contacts,applied the voltage of the discharge capacitor 411 across the flash tube 412, the latter having received previously a fraction of this voltage, the value of which fraction is determined by the

resistances

404 and 423, and to the tube firing circuit consisting of a capacitor 413 and a transformer 414, thus firing the flash. When the thyristor 401 becomes conductive due to the subject having been sufficiently illuminated, it discharges the capacitor 402, which was previously charged, into the thyristor 421, which results in reversing the anode voltage of the thyristor for a short period so as to cause it to block and thus arrest the'discharge of the capacitor 411. The capacitance value of the capacitor 402 is selected so as to obtain an impulse of sufficient duration to allow the extinction, or blocking, of the thyristor 421. The capacitance value of the capacitor 422 is selected so as to obtain the shortest possible impulse so that the extinction of the thyristor 421 may occur as rapidly as possible. The

resistances

424 and 425 are used to polarize the capacitor 422. The value of resistance 403 must be selected in order to give a current lower than the maintenance current of the thyristor 401 so as to prevent the capacitor 411 from continuing to discharge itself through the thyristor 401. A compensation device, such as an induction coil, 415 modifies the discharge impulse in the flash tube. Among other things, it lengthens the discharge duration, etc.

FIG. shows a control device combined with an electronic gate and with an optical device for the regulation of sensitivity. This control device consists of an electronic device 50 and the photoflash 51.

The components and operation of this device are identical to those described with reference to FIG. 3, with the difference that an impulse transmitted by the capacitor 506 opens a semi-conductor switch, or a special arc arrester, etc., 508, via its firing circuit and thereby extinguishes the flash tube 512 of the photoflash while discharging the capacitor 513 of the latter.

In FIG. 6, we describe another embodiment equipped with a special arc arrester combined with an electronic gate and with an electric device having several capacitors for the regulation of sensitivity. A special arc arrester 611 and its firing device, which consists of the thyristor606, the

resistances

607 and 608, the capacitor 609 and-the transformer 610, serve as a substitute for the thyristor 508 of FIG. 5. Here, we make use of an electric circuit for adjusting the sensitivity, the circuit consisting of a switch 615 connected to select one of the capacitors 603 and 604 having different capacitance values.

In FIG. 7 there is shown another embodiment in which the photodiode is replaced by a phototransistor 702 in order to give a higher sensitivity to the light integrator than .is possible with the photodiode. In FIG. 8 the photodiode 802 has an amplification circuit composed essentially of an npn transistor 803 which allows the selection of a very high sensitivity, as a function of the gain of the transistor.

In FIG. 9 a pnp transistor 903 replaces the npn transistor.

In FIG. 10 the light sensor is a photovoltaic cell, such adjusted by selecting suitable values for the

resistances

1215 and 1203.

In FIG. 13 we use a circuit with a four-layer diode constituting a unilateral, bilateral switch, etc. as the level detector and at the same time as the firing impulse generator for the thyristor 1306.

In FIG. 14 the control device contains a voltage divider circuit which consists of the

capacitors

1401 and 1403 instead of a Zener diode, a capacitor and a resistance as in the previous arrangements.

In FIG. 15 the control circuit contains a phototransistor 1502 and an electric device for regulating the sensitivity. The latter device consists of a switch 1516 which permits a selection of either one of the

resistances

1503 and 1504, the value of the resistance selected determining the effective sensitivity of phototransistor 1502 and, therefore, the device sensitivity.

In FIG. 16 there is shown a scale device intended for permitting an external regulation of the sensitivity, i.e., related to focal distance, or range, and/or diaphragm apertures. Moreover, we have combined this device with the usual focal distance aperture calculator of electronic photofiashes and with other improvements as well. This regulating device consists of a fixed interchangeable disc 1601 and a rotatable and selflocking disc 1604 coupled to the device for regulating the sensitivity of the control device.

Graduated in degrees DIN, scale 1603 on disc 1601 is provided for setting'the film sensitivity, and graduated in meters, scale 1602 is provided for setting distances. In the case of a photographic camera fitted with an adjustable diaphragm, the disc 1604 is to be rotated so as to bring the desired aperture indication on scale 1607 right opposite the sensitivity figure on scale 1603 for the film being utilized. The zone 1605 of disc 1604 shows on scale 1602 the range of distances for which the control device will work accurately.

Another way of using this same device is to select the focal distance, or range, and read the aperture to be used opposite the sensitivity figure for the film being used.

' For use with a photographic camera fitted with a fixed diaphragm, as for example the Minox camera with a 3.5 aperture, the disc 1604 is rotated so as to bring the Minox" pointer 1609 oppositethe sensitivity for the film being used on scale 1603. The zone 1605 of the disc 1604 shows on scale 1602 the range of distances for which the control device can work accurately.

If the control device is not to be used, one must rotate the disc 1604 so as to bring the NA pointer (=nonautomatic) 1606 opposite the sensitivity figure of the film used on scale 1603.

The

scales

1608 and 1602 are used in the same manner as those of a customary distance aperture calculator. This operation results in'setting the control device sensitivity to the starting, or zero point, which means that it is out of action.

This device may advantageously be combined with a light source 1610 which allows easier use and reading.

The same device may also be combined with the following luminous indicators:

for the charge of the photoflash capacitor 1611;

for the control device, to indicate whether it functions or not, (functioning 1612, not functioning 1613);

for the achievement of the functioning of the control device 1614.

FIG. 17 shows essentially the same device as FIG. 16, but the device of FIG. 17 is in the shape of a fixed and interchangeable guide strip 1701 and a sliding and selflocking slider 1704.

In FIG. 18 there is shown a control device which is fundamentally identical to that of FIG. 15, but equipped for manual regulation. In this case, the light sensor is replaced by a variable resistance 1801 whose setting determines the period required for the capacitor 1802 of the integrator to reach its triggering charge.

In FIG. 19 there is shown an optical control and indicator device for operating the control device. This optical device consists of a fiber-optic element 1902 one end of which is placed on the special arc arrester 1901 which emits light when actuated. The other end of the I regulation scale unit.

Possibly, a complementary optical system 1904 can be used to further increase the visibility of this indicator.

In FIG. 20 there is .shown one embodiment of the above-mentioned special gas-filled tube of the arc arrester type. This consists of an electrically isolating enclosure 2003, which can be transparent, translucent or opaque, whose interior 2005 is filled with a gas, preferably argon and contains two preferably identical and

unpolarized electrodes

2001 and 2002. A third firing electrode 2006 is arranged outside the enclosure 2003 and is extended by the connecting wire 2007. The

electrodes

2001 and 2002 are located and formed in such a way, and the filling and the pressure of the gas are chosen in such a manner, that this tube will function to perform an arc operation. The modified embodiment of FIG. 21. has a firing electrode 2106 which protrudes into the gas-filled interior 2105 of the enclosure 2103.

As can be seen from FIGS. 20a and 21a, which show modified embodiments of the devices of FIGS. 20 and 21, the

enclosures

2003 and 2103 are formed in the shape of tubes and are delimited by two electrodes of the socket" type, and oflarge surface area. The length of this tube is about the same as its diameter.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

I. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a controlsignal representing the time integral of the received light intensity, the improvement comprising an electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor for generally conserving energy from said capacitor when the control signal from said integrator reaches a predetermined value.

2. In adevice for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising an electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, said electronic switch being conducting when an electric current is flowing through the element, and the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor for generally conserving energy from said capacitor when the control signal from said integrator reaches a predetermined value.

3 An arrangement as defined in claim 2 wherein said electronic switch is composed of a semiconductor element. r I

4. An arrangement as defined in claim 3 wherein said semiconductor element is constituted by a gate turn off switch.

5. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising a normally conducting electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected tosaid integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor when the control signal from said integrator reaches a predetermined value.

6. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected.

from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the out-' put from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising an electronic gate turn off switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor when the control signal from said integrator reaches a predetermined value.

7. A control circuit for controlling the operation of flash tube means wherein electrical energy is supplied to said tube means from a supply source for causing said tube means to emit a light flash and wherein the passage of current through said tube means is controllable for conserving energy of the supply source, said control circuit comprising a supply source,

electronic switch means having a pair of main current carrying electrodes, and having a control electrode for receiving an electrical signal for rendering said switch means conductive,

biasing means connected to normally apply a biasing voltage across said switch means when said switch is in its nonconductive state, circuit means coupling the main electrodes of said switch means in series with said tube means and said supply source to enable, when said switch means is rendered conductive, passage of current between said pair of main current carrying electrodes to cause ionization of said tube means whereby generation of a light flash therefrom occurs, and

control means coupled with said electronic switch means and responsive to light sensing means to render said electronic switch means nonconductive and cause termination of said light.

8. A circuit as in claim 7 wherein said biasing means includes voltage divider means coupled with said switch means for normally applying a biasing voltage across the main electrodes of said switch means.

9. A circuit as defined in claim 7 wherein said control means includes a second electronic switch means coupled with said first-named electronic switch means and coupled with light sensing means for sensing light emitted by said lamp means for causing reversal in the polarity of the voltage across the main electrodes of said first-named switch means upon receipt by said light sensing means of a predetermined amount of light.

10. A circuit as in claim 9 wherein said second switch means comprises a gas-filled tube having two main electrodes and'a firing electrode, said firing electrode being responsive to said light sensing means.

11. A circuit as in claim 9 wherein each of said electronic switch means comprises a thyristor.

12. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

electronic switch means having a pair of main current carrying electrodes by which it is connected in se ries between the load element and the supply source, said switchmeans being electrically coupled with triggering means of said load element and having a controlelectrode for receiving an electrical signal which renders said switch means conductive for passing current therethrough to said triggering means .to cause said load element to ionize whereby a light flash is produced; and flash terminating means connected between said sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said sensing means, to cause termination of the light flash and generally conserve energy of said supply source. 7 13. An arrangement as defined in claim 12 wherein said triggering means comprises a trigger transformer and energy source electrically connected to said switch means.

14. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is'operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means being electrically connected with triggering means of said load element for passing current to said triggering means for ionizing said load element whereby a light flash is produced by said load element; and

flash terminating means connected between said sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said sensing meansto terminate the light flash and generally conserve energy of said supply source.

15. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in c0mbination:

a load element comprising a flash lamp and trigger means therefor;

electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means being electrically coupled with said flash lamp and said trigger means, and the conduction of current through said switch means causing both said trigger means to ionize said lamp and said lamp to generate a light flash; and

flash terminating means connected with light sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said light sensing means to terminate the light flash from said lamp and enableconservation of energy of said supply source.

16. A circuit for controlling the operation of a load element which'converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means having biasing means coupled therewith to apply voltage across the switch means when said switch means is nonconductive, and having a control electrode for receiving an electrical signal for rendering said switch means conductive for passing electrical current therethrough to ionize said load element whereby said load element produces a light flash;

second electronic switch means having two main electrodes and a control electrode; means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source; and v said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source. 17. A circuit as defined in claim. 16 wherein said second electronic switch means is constituted by a gasfilled tube having two main electrodes and one firing electrode and constructed to operate by producing an arc.

18. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, means establishing a voltage across said switch means when said switch means is nonconductive, and said switch means having a control electrode coupled in series with a voltage source and synchronization contact means for receiving an electrical signal which renders said switch means conductive for applying electrical energy to said load element for producing a light flash;

second electronic switch means having two main electrodes and a control electrode;

means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source;

said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source; and

inductance means in series with said load element and said first electronic switch means for modifying the current impulse to said load element. 19. A circuit as defined in claim 18 wherein said second electronic switch comprises a gas-filled tube having two main electrodes and a firing electrode, said firing electrode being responsive to said light sensing means.

20. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source and having a control electrode for receiving an electrical signal which renders said switch conductive for applying electrical energy to said load element for producing a light flash;

second electronic switch means having two main electrodes and a control electrode; and

means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source; said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source;

said load element having a trigger input which initiates the converting of an electric current from the supply source into a light flash when a signal is applied to the trigger input, and said first electronic switch means being connected with both the load element and said trigger input for enabling current flow through the first electronic switch means to cause the trigger input to ionize the load element and enable the load element to generate a light flash.

circuit means connecting said electronic switch I means with said flash tube means and said supply source, said circuit means connecting the main 1 electrodes of said switch means in series with said tube means and said supply source and including biasing means for establishing a voltage across said switch means when said switch means is nonconductive, and including means for applying a signal to said control electrode to render said switch means conductive for (a) enabling current flow between said pair of main current carrying electrodes before said flash tube means ionizes and (b) causing a light flash to be' generated by said tube means, and

control means coupled with said electronic switch means and responsive to light sensing means to render said electronic switch means nonconductive and cause termination of said light flash.

22. A control circuit as in claim 21 wherein said flash tube means includes a flash tube and trigger means therefor, and

said circuit means includes means coupling said switch means in series with both said tube and trigger means, and said biasing means includes voltage divider means coupled with the main electrodes of said switch means for establishing said voltage across said switch means.

23. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination:

first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, and having a control electrode for receiving an electrical signal which renders said switch means conductive for applying electrical energy to said load element for producing a light,

a gas-filled tube having two closely spaced main electrodes and one firing electrode and operative as a switch,

means connecting one main electrode of said gasfilled tube to one of said main electrodes of said first electronic switch means, and commutating capacitor means connected between said other main electrode of said gas-filled tube and the junction of said first electronic switch means and said load element;

an inductance coil connected in series between said source and said first electronic switch means and said gas-filled tube means for reducing current impulses thereto; and

said control electrode of said gas-filled tube being connected to light sensing means for receiving the electrical signal produced thereby to render said gas-filled tube conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash from said load element to generally conserve energy of said supply SOUI'CC.

Claims

1. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising an electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitOr for generally conserving energy from said capacitor when the control signal from said integrator reaches a predetermined value.

2. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising an electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, said electronic switch being conducting when an electric current is flowing through the element, and the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor for generally conserving energy from said capacitor when the control signal from said integrator reaches a predetermined value.

3. An arrangement as defined in claim 2 wherein said electronic switch is composed of a semiconductor element.

5. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising a normally conducting electronic switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor when the control signal from said integrator reaches a predetermined value.

6. In a device for controlling the operation of an element which converts an electric current into a light flash and including a storage capacitor storing energy for supplying the element, a light sensor arranged for sensing light produced by the element and reflected from an object and for producing an electrical output proportional to the intensity of the light which it receives, and an integrator connected to receive the output from the sensor and to produce a control signal representing the time integral of the received light intensity, the improvement comprising an electronic gate turn off switch having two main electrodes via which said switch is connected in series between said capacitor and said element, and having a control electrode connected to said integrator to receive the control signal from said integrator, the application of the control signal to said control electrode rendering said switch nonconductive and thus opening the circuit between said capacitor and said element and halting the discharge of said capacitor when the control signal from said integrator reaches a predetermined value.

7. A control circuit for controlling the operation of flash tube means wherein electrical energy is supplied to said tube means from a supply source foR causing said tube means to emit a light flash and wherein the passage of current through said tube means is controllable for conserving energy of the supply source, said control circuit comprising a supply source, electronic switch means having a pair of main current carrying electrodes, and having a control electrode for receiving an electrical signal for rendering said switch means conductive, biasing means connected to normally apply a biasing voltage across said switch means when said switch is in its nonconductive state, circuit means coupling the main electrodes of said switch means in series with said tube means and said supply source to enable, when said switch means is rendered conductive, passage of current between said pair of main current carrying electrodes to cause ionization of said tube means whereby generation of a light flash therefrom occurs, and control means coupled with said electronic switch means and responsive to light sensing means to render said electronic switch means nonconductive and cause termination of said light.

10. A circuit as in claim 9 wherein said second switch means comprises a gas-filled tube having two main electrodes and a firing electrode, said firing electrode being responsive to said light sensing means.

12. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means being electrically coupled with triggering means of said load element and having a control electrode for receiving an electrical signal which renders said switch means conductive for passing current therethrough to said triggering means to cause said load element to ionize whereby a light flash is produced; and flash terminating means connected between said sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said sensing means, to cause termination of the light flash and generally conserve energy of said supply source.

13. An arrangement as defined in claim 12 wherein said triggering means comprises a trigger transformer and energy source electrically connected to said switch means.

14. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means being electrically connected with triggering means of said load element for passing current to said triggering means for ionizing said load eleMent whereby a light flash is produced by said load element; and flash terminating means connected between said sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said sensing means to terminate the light flash and generally conserve energy of said supply source.

15. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: a load element comprising a flash lamp and trigger means therefor; electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means being electrically coupled with said flash lamp and said trigger means, and the conduction of current through said switch means causing both said trigger means to ionize said lamp and said lamp to generate a light flash; and flash terminating means connected with light sensing means and said switch means for rendering said switch means nonconductive upon the production of a signal by said light sensing means to terminate the light flash from said lamp and enable conservation of energy of said supply source.

16. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, said switch means having biasing means coupled therewith to apply voltage across the switch means when said switch means is nonconductive, and having a control electrode for receiving an electrical signal for rendering said switch means conductive for passing electrical current therethrough to ionize said load element whereby said load element produces a light flash; second electronic switch means having two main electrodes and a control electrode; means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source; and said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source.

17. A circuit as defined in claim 16 wherein said second electronic switch means is constituted by a gas-filled tube having two main electrodes and one firing electrode and constructed to operate by producing an arc.

18. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, means establishing a voltage across said switch means whEn said switch means is nonconductive, and said switch means having a control electrode coupled in series with a voltage source and synchronization contact means for receiving an electrical signal which renders said switch means conductive for applying electrical energy to said load element for producing a light flash; second electronic switch means having two main electrodes and a control electrode; means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source; said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source; and inductance means in series with said load element and said first electronic switch means for modifying the current impulse to said load element.

19. A circuit as defined in claim 18 wherein said second electronic switch comprises a gas-filled tube having two main electrodes and a firing electrode, said firing electrode being responsive to said light sensing means.

20. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source and having a control electrode for receiving an electrical signal which renders said switch conductive for applying electrical energy to said load element for producing a light flash; second electronic switch means having two main electrodes and a control electrode; and means connecting one main electrode of said second electronic switch means to one of said main electrodes of said first electronic switch means, and means connecting the other main electrode of said second electronic switch means to a voltage source; said control electrode of said second electronic switch means being connected to said light sensing means for receiving the electrical signal produced thereby to render said second switch means conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash for generally conserving energy of said supply source; said load element having a trigger input which initiates the converting of an electric current from the supply source into a light flash when a signal is applied to the trigger input, and said first electronic switch means being connected with both the load element and said trigger input for enabling current flow through the first electronic switch means to cause the trigger input to ionize the load element and enable the load element to generate a light flash.

21. A control circuit for controlling the operation of flash tube means wherein electrical energy is supplied to said tube means from a supply source for causing said tube means to emit a light flash and wherein the passage of current through said tube means is controllable for conserving energy of the supply source, said control circuit comprising a supply source, electronic switch means having a paiR of main current carrying electrodes and a control electrode, circuit means connecting said electronic switch means with said flash tube means and said supply source, said circuit means connecting the main electrodes of said switch means in series with said tube means and said supply source and including biasing means for establishing a voltage across said switch means when said switch means is nonconductive, and including means for applying a signal to said control electrode to render said switch means conductive for (a) enabling current flow between said pair of main current carrying electrodes before said flash tube means ionizes and (b) causing a light flash to be generated by said tube means, and control means coupled with said electronic switch means and responsive to light sensing means to render said electronic switch means nonconductive and cause termination of said light flash.

22. A control circuit as in claim 21 wherein said flash tube means includes a flash tube and trigger means therefor, and said circuit means includes means coupling said switch means in series with both said tube and trigger means, and said biasing means includes voltage divider means coupled with the main electrodes of said switch means for establishing said voltage across said switch means.

23. A circuit for controlling the operation of a load element which converts an electric current from a supply source into a light flash and which is operatively associated with means for sensing the light produced by the element and producing a signal when a predetermined quantity of light has been produced, said circuit comprising, in combination: first electronic switch means having a pair of main current carrying electrodes by which it is connected in series between the load element and the supply source, and having a control electrode for receiving an electrical signal which renders said switch means conductive for applying electrical energy to said load element for producing a light flash; a gas-filled tube having two closely spaced main electrodes and one firing electrode and operative as a switch, means connecting one main electrode of said gas-filled tube to one of said main electrodes of said first electronic switch means, and commutating capacitor means connected between said other main electrode of said gas-filled tube and the junction of said first electronic switch means and said load element; an inductance coil connected in series between said source and said first electronic switch means and said gas-filled tube means for reducing current impulses thereto; and said control electrode of said gas-filled tube being connected to light sensing means for receiving the electrical signal produced thereby to render said gas-filled tube conductive for supplying a voltage at a main electrode of said first switch means which reverses the polarity of the voltage across the main electrodes of said first switch means and thus renders said first switch means nonconductive to cause termination of the light flash from said load element to generally conserve energy of said supply source.