US 3873882 A
An emergency or auxiliary lighting system for a gaseous discharge lamp is provided with an auxiliary lamp controlled by a switch which is biased to remain in a closed position. A control circuit, responsive to the voltage across the gaseous discharge lamp, produces a voltage proportional thereto which is opposed to the biasing control. During any time that the gaseous discharge lamp provides more than a minimum adequate light output, the control circuit voltage becomes greater than the biasing control to open the switch. Also, in the event of a power interruption, the control circuit closes the switch.
Claims available in
Description (OCR text may contain errors)
United States Patent Gershen AUXILIARY LIGHTING SYSTEM FOR A GASEOUS DISCHARGE LAMP Bernard J. Gershen, Centerport, N.Y.
Assignee: Leviton Manufacturing Co., Inc.,
Little Neck, NY.
Filed: Oct. 5, 1973 Appl. N0.: 403,948
u.s. c1 315/92, 315/91, 315/120, 315/135 1m. (:1. H05b 41/46, H05b 37/04 Field of Search 315/88, 91, 92, 119, 120, 315/121,127,129,130,131, 135,178,182
3,783,332 l/1974 Peterson ct al. 3l5/9l Primary ExaminerR. V. Rolinec Assistant Examiner-E. R. LaRoche Attorney, Agent, or Firm-Hanse l-l. Hamilton  ABSTRACT An emergency or auxiliary lighting system for a gaseous discharge lamp is provided with an auxiliary lamp controlled by a switch which is biased to remain in a closed position. A control circuit, responsive to the voltage across the gaseous discharge lamp, produces a voltage proportional thereto which is opposed to the biasing control. During any time that the gaseous discharge lamp provides more than a minimum adequate light output, the control circuit voltage becomes greater than the biasing control to open the switch. Also, in the event of a power interruption, the control circuit closes the switch.
6 Claims, 4 Drawing Figures AUXILIARY LIGHTING SYSTEM FOR A GASEOUS DISCHARGE LAMP BACKGROUND OF THE INVENTION This invention relates to anemergency lighting system, and more particularly to an auxiliary lighting circuit for use with a primary lighting system.
Gaseous discharge lamps, such as mercury arc lamps, metal are lamps and similar type lamps, have long been used in industrial lighting facilities as well as on highways because of their extremely high efficiency when compared to other sources of light. This type of lamp has the property of requiring a relatively high voltage for striking the arc to light the lamp, and requires a relatively lower voltage for maintaining the arc. These requirements are handled by various types of ballasts which are commercially available.
One of the problems in using such gaseous discharge lamps resides in the fact that, upon interruption of power for a few cycles, the lamp will become extinguished andrestriking of the are within the lamp will not occur immediately upon restoration of the power source. One reason for this is that the striking potential of a hot lamp is much higher than the striking potential when the lamp is cool. Thus, when the gaseous discharge lamp is initially turned on while in a cool state, the ballast will provide sufficient voltage to strike an arc in the lamp. After the lamp has been operating for a length of time, it heats up and should a power interruption occur, a return of power to the line of the hot lamp will require a greater striking potential than the ballast is capable of providing. The lamp will therefore not immediately strike and may require as much as fifteen minutes to cool sufficiently before the ballast voltage will restrike the are. If this should occur in a factory or office, a safety hazard may very well result. Similarly, when used in highwaysthe absence of sufficient lighting for a length of time may contribute to the occurrence of accidents or other resulting emergencies.
An additional problem which occurs when using gaseous dischargelamps resides in the fact that once the arc is struck there is an initial warmup of the gaseous discharge until the potential across the lamp provides adequate lighting output.
To facilitate the use of gaseous discharge lamps it is desirable to provide an emergency or auxiliary lighting circuit in conjunction with the gaseous discharge lamp to provide illumination during the off and warm-up periods ofthe lamp. While various circuits have been suggested in the past for providing such emergency illumination, such circuits have in general been relatively complicated, expensive, inefficient, and have employed many components.
Many of the circuits available in the prior art only provide auxiliary lighting which will solve the first of the aforementioned problems. Namely, the auxiliary lighting circuits will be only turned on after a power interruption while the gaseous discharge lamp is cooling off awaiting restriking by the ballast output voltage. However, these prior art circuits will turn off as soon as the gaseous discharge lamp has been restruck. Therefore, during the period of time that the gaseous discharge lamp has not reached sufficient illumination to provide normal desired lighting output, the auxiliary circuit will not provide any assistance to compensate for such lack of proper illumination.
Other known devices do provide auxiliary lighting which will respond to both aforementioned problems. Namely, in addition to the auxiliary lighting being turned on following a power interruption, this auxiliary lighting will also remain on during the warm-up period until the gaseous discharge lamp reaches the normal desired illumination output level. However, most of these circuits make use of relays involving a relay coil in series or in parallel with the ballast output. This requires stringent manufacturing restrictions on the design of the relay coil such that it will not have an adverse effect on the gaseous discharge lamp wattage. Furthermore, the use of relay coils necessarily involves an electromechanical device which is not always reliable. In addition, these prior art circuits generally require two switching devices wherein oneof the switching devices controls the turning on of the auxiliary lighting during the initial warm-up period, while the second switching device serves to disconnect the first switching device during power interruption such that the auxiliary lighting will remain turned on.
SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel emergency or auxiliary lighting system for gaseous discharge lamps which avoids the aforementioned problems of the prior art devices.
Another object of the invention is to provide an emergency lighting circuit for gaseous discharge lamps which does not contain relay switches.
Yet another object of the invention is to provide an emergency lighting system for gaseous discharge lamps which uses a single switching element to provide auxiliary illumination both during initial warmup of the gaseous discharge lamp as lamp as during the cooling off period required after a power interruption of the gaseous discharge lamp.
Still a further object of the invention is to provide an emergency lighting system for gaseous discharge lamps which is relatively inexpensive and uncomplicated as well as highly efficient.
These and other objects of the present invention will be apparent from a reading of the following description and accompanying drawings. In accordance with one aspect of the present invention an emergency or auxiliary lighting circuit is provided in conjunction with a gaseous discharge lamp which includes a single switch means characterized by the absence of solenoid operated contacts. The switch is biased in a normally closed position. A control circuit is provided for the switch which operates in opposition to the bias means. The output voltage of the control circuit is proportional to the voltage across the lamp and thus increases as the lamp warms up. As this output voltage reaches a predetermined value, corresponding to the voltage across the gaseous discharge lame when the lamp reaches the desired output illumination, the control circuit dominates over the biasing means and opens the switch means, thereby turning off the auxiliary light sourse. The control circuit senses the high voltage output of the ballast which occurs when power is restored after an interruption and the gaseous discharge lamp is cooling off prior to being restruck by the voltage output from the ballast. This insures that the auxiliary light device will remain on during the cooling off period until the gaseous discharge lamp is restruck. lmmediately following the restriking of the lamp, however, as the gaseous discharge lamp again warms up to provide the desired illumination output, the auxiliary lighting circuit will also remain on under control of the biasing means.
In a preferred embodiment of the invention the switch means is a reed switch controlled by an electromagnetic coil and includes a permanent magnet biasing the reed switch into closed position. The flux from the electromagnetic coil is fixed to operate in a direction opposite to that of the magnetic field provided by the permanent magnet.
In a second embodiment the switch is an SCR having its gate positively biased and having the voltage across the gaseous discharge lamp transformer coupled, recti tied and inverted to serve as a negative control voltage acting in opposition to the positive bias on the gate. A unidirectional switch is used as the high voltage sensing device which overrides the negative control voltage, thereby permitting the biasing voltage to hold an SCR in a conducting state until after the striking of the arc in the gaseous discharge lamp has occurred.
BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more clearly understood by referring to the drawings wherein similar reference characters denote similar elements throughout the views, and in which:
FIG. 1 is a graph illustrating the voltage across the gaseous discharge lamp as a function of time.
FIG. 2 shows the on and off state of the auxiliary lamp device as a function of time.
FIG. 3 is a schematic diagram illustrating one embodiment of the emergency lighting system in accordance with the present invention.
FIG. 4 is a schematic diagram of an emergency lighting system in accordance with another embodiment of the present invention.
DESCRIPTION OF THE INVENTION FIG. 1 illustrates a graph of the lamp voltage plotted as a function of time which will be useful in understanding the present invention. It is assumed, by way of example, that the circuit contains a gaseous discharge lamp with a ballast providing voltage there-across with a maximum voltage of approximately 250 volts. When the lamp is initially turned on at time T1, the ballast provides 250 volts to strike an arc in the cold lamp. The ballast provides its full output voltage at this point which, in turn, ionizes or breaks down the are, causing it to strike. As soon as the arc is struck the voltage across the lamp drops to approximately 25 volts. As the arc heats up between times T1 and T2, there is a relatively low light output as the voltage increases across the lamp to approximately 85-90 volts at the time T2. At this point there is a minimum acceptable light output from the lamp. However, the light intensity, as well as the voltage, continues increasing until time T3 at which time the normal operating condition for the lamp is reached. At time T3 the voltage across the lamp is approximately 135 volts with the lamp in a normal fully on condition.
Assume next that a power interruption occurs at time T4. This interruption may result from an opening of the power source by tripping of a circuit breaker due to momentary overloading conditions, etc. Assume further that the power is turned on again at T5 following the interruption which occurred at T4. Immediately the ballast potential rises to 250 volts. The lamp however does not light because it is still in a hot condition and its hot striking potential is higher than 250 volts. The unlit lamp therefore begins to cool and after a certain length of time, until T6, the lamp has cooled sufficiently for the 250 volts provided from the ballast to restrike the are. When this occurs, the operation of the lamp repeats similarly to that described for a cold start wherein the time interval from T6 to T7 reflects the warmup time required for the lamp voltage to rise to approximately volts. During the time interval from T7 to T8, there is minimal desired or acceptable light output until the normal operating condition for the lamp is reached.
As is evident from the graph of FIG. 1, during the time interval between T1 and T2, although the lamp is struck, there is in fact insufficient light output from the lamp. Furthermore, following a power interruption such as that illustrated during the time interval between T5 to T6, the lamp will remain totally in an off state without providing any light. Thereafter, again, an insufficient illumination will be provided by this lamp between times T6 and T7.
In order to alleviate the problem resulting from the use of gaseous discharge lamps it would be beneficial and it is within the scope of this invention to provide an auxiliary lighting system which is capable of turning on during the time following a power interruption. As is generally well known in the art, an incandescent lamp has been typically used for auxiliary systems, since such lamps can be turned on immediately without any delay. It is therefore necessary to provide a switch for use in conjunction with the incandescent lamp in a configuration wherein the switch operates during the required time periods. Referring now to FIG. 2, it can be seen that it is necessary that the switch operate in an on state between times T1 and T2 during the warmup time of the gaseous discharge lamp when there is insufficient light output. Similarly, between times T5 and T6 following power interruption the incandescent lamp should remain on and should continue in this on state until time T7 when the gaseous discharge lamp has reached its minimal acceptable light output and whereupon the incandescent lamp can then turn off.
Referring to FIG. 3, a schematic diagram is shown illustrating one embodiment of the emergency lighting system in accordance with the present invention. The main lighting system includes a gaseous discharge or are lamp 10 connected to the output terminals of a ballast 12 which is, in turn, supplied with a source of power from an AC (alternating current) supply 14. The ballasLneed not be of any special type such as a lead or lag type ballast device, but any standard ballast can be used. The voltage across the gaseous discharge is also placed across a rectifier 16 which is shown by way of example as a diode bridge rectifier. Capacitor 18 in series with the rectifier l6 acts as a voltage limiting device. While the diode bridge rectifier has been shown, it is to be understood that other types of devices coming within the scope of this invention may be used, such as, for example, a transformer with a pair of appropriately poled diodes in its secondary circuit.
The output from the rectifier is applied to the electromagnetic coil 20 of a reed switch shown generally at 22. Capacitor 24 is connected in paralled relationship with respect to the rectifier output to filter the rectifier output.
One contact of the reed switch 22 is connected to the gate electrode of triac 30. A triac, ,as is well known, is an alternating current semiconductor controlled switch having a single control or gate electrode and a proper signal when applied to the gate causes the triac to conduct current. As long as the signal is present feeding the gate, the triac will remain in a conducting condition. A
resistor 32 is connected in series with the gate of the triac and limits the gate current to a safe value.
The auxiliary lamp 34 is connected in series with the triac 30 to one side of the AC supply. Thus, when the triac is in a conductive condition, the auxiliary lamp will be turned on. This condition will exist whenever the reed switch is closed.
The reed switch 22, as is well known, usually contains two opposing flat reeds A and 20B of magnetic material which are supported as cantilevers with their free ends overlapping and separated by a small gap. Surrounding the reeds 20A and 20B is the electromagnetic coil 20 so placed that the magnetic field of the coil encloses the reeds. When the coil 20 is energised, its magnetic flux pulls the reeds 20A and 20B together bringing them into contact and completing thecircuit to the gate of the triac 30. The flux can be in either direction but must be of sufficient magnitude to cause the reeds to close. As shown in FIG. 3, a permanent magnet 36 is located adjacent to the reed switch structure and provides a fixed magnetic bias, thereby keeping the reed switch in a closed condition. Thus, in the presence of low voltage across the arc lamp terminals, the reed switch will remain in a closed condition and the auxiliary lamp will be turned on. The electromagnetic coil 20 is in such a position, and is connected in such a direction, that the magnetic field produced by it opposes the permanent bias magnet field.
in operation, during the time period from T1 to T2, as the voltage is increasing across the gaseous discharge lamp, the electromagnetic coil 20 is energized and produces a flux opposing the permanent bias magnet field. However, voltage is low and the resulting electromagnetic field is insufficient to overcome the field of the permanent magnet. Therefore, the reeds in the switch remain closed and the auxiliary lamp remain, on. At time T2, however, a sufficient voltage is present across the gaseous discharge lamp to cause the coil 20 to produce a field which balances the field produced by the permanent bias magnet 36, but which is in an opposite direction. As a result, there is no net magnetic field enclosing the reeds and the contacts of the reed switch 22 open. From time T2 to T3, the voltage continues to increase across thegaseous discharge lamp and the magnetic field from the electromagnetic coil 20 continues to increase in a direction opposite to that of the permanent bias magnet. However, the total net field produced in a single direction acting upon the reed switch contacts is insufficient to cause them to close. The reed switch therefore remains open and the auxiliary lamp remains in an of condition. This phenonenon continues from time T3 to T4 wherein the electromagnetic field remains constant but yet sufficient to cause the reed switch to close.
At time, T4, we can assume for purposes of illustration that the power is interrupted and the electromagnetic field produced by the coil 20 will be reduced to zero, permitting the permanent bias magnet to take over closing the reed switch. However, at T5, if the power is restored, although the gaseous discharge lamp remains off, the ballast voltage is relatively high (250 volts), and as a result, the field produced by the electromagnetic coil 20 is high enough to overcome the permanent bias magnet field and to reclose the reed switch. It is to be remembered that the reed switch will close with a flux in either direction. Thus, even though the flux in this case is opposite to that of the flux from the permanent bias magnet, the reed switch responds to a sufficient difference in the magnetic flux and will close in response thereto. The reed switch remains closed and the triac conducts current from time T5 until time T6 when the gaseous discharge lamp is restruck. At that time, the voltage across the gaseous discharge lamp is suddenly reduced to a very low value (30 volts). The field from the electromagnetic coil 20 is therefore also reduced to a low value. However, at this time the flux from the permanent bias magnet controls and the reed switch will remain closed under the influence of the permanent bias magnet. As the control of the switch transfers from the flux in one direction from the electromagnetic coil to the flux in opposite direction from the permanent bias magnet, a flicker of the incandescent lamp 34 may occur. The slight flicker however can be reduced by increasing the size of the filter capacitor 24 thereby increasing its energy storage capability to prevent noticeable flicker of the auxiliary lamp 34. The auxiliary lamp remains in its on state until time T7 when the gaseous discharge lamp has sufficient voltage across it to provide acceptable illumination.
Although the circuit has been shown including the triac 30, it is to be understood that the triac 30 may be eliminated and the current flowing through the reed switch may feed directly to the auxiliary lamp. However, because of the restricted current carried by the reed switch 22, this could restrict the voltage of the auxiliary lamp 34. It is nevertheless seen however, that a single switch element, namely the reed switch 22, can be used to detect both the conditions of high voltage and low voltage across the gaseous discharge lamp which occur, during its operation.
Referring now to FIG. 4, there is shown another embodiment of this invention where the gaseous discharge lamp 40 is placed across the output of the ballast 42 which is, in turn, energized by an AC source 44. Connected to the output of thegaseous discharge lamp 40 is a transformer 46 having a primary 46a and a secondary 46b with appropriately poled diodes 48, 50 connected to the secondary. If desired, a current limiting resistor 47 may be connected in series with the primary 46a. Although a transformer is shown it is to be understood that a rectifier diode bridge may also be used as well as an auxiliary winding on the ballast to monitor the lamp voltage. The ends of the secondary of the transformer are interconnected at terminal 52 and the output is connected through limiting resistor 54 to one side of capacitor 56. The other side of capacitor 56 is connected to a tapped mid-point 58 of the secondary of the transformer 46. Thus, the voltage at point 60 will be negative with respect to the voltage at point, 62. A resistor 64 is connected to the resistor 54 and to the capacitor 56 to filter the output from the diodes 48 and 50. The magnitude of the voltage across the capacitor 56 will be proportional to the voltage across the gaseous discharge lamp, but will be a negative voltage.
The AC source 44 is also connected across opposite terminals of a rectifier containing a diode bridge arrangement 66. The opposite arms of the'diode bridge are connected to a series circuit containing a quick starting auxiliary lamp 68 in series with the anode and cathode of an SCR 70. The gate of the SCR is connected through a resistor 72 to a positive voltage from the diode bridge 66. it is also coupled to the negative voltage signal from the capacitor 56 through a resistor 74 and an additional capacitor 76. A unidirectional switch 78 is also connected in parallel across the capacitor 56 and the resistor 64 and receives the negative voltage therefrom.
As is well known in the art, the unidirectional switch 78 operates such that for voltages lower than its breakdown voltage, the switch does not conduct and thus for all practical purposes is not seen by the circuit. When the breakdown voltage of the switch 78 is reached, the device goes into an avalanche mode of operation and can support only a relatively low voltage across it. When it is in the avalanche mode of operation, should current through the device drop below a specified holding current, the device reverts back to its nonconducting state.
In operation, from the time T1 to T2, when the gaseous discharge lamp is in the warmup stage, there is a relatively low voltage across the lamp, Thus, the magnitude ofthe negative voltage feeding the gate of SCR 70 will be less than the positive bias-voltage from the resistor 72 and the SCR will be in a conducting state, thereby keeping the auxiliary lamp 68 on. As the voltage across the gaseous discharge lamp continues to increase between time T2 and T3, the magnitude of the negative voltage feeding the gate of SCR 70 increases greater than the positive bias from the resistor 72 and will turn off the SCR 70, thereby extinguishing the auxiliary lamp 68. The auxiliary lamp 68 will remain off be- .tween times T3 and T4 or until a power interruption occurs.
At time T4, when the power is momentarily interrupted, the entire system is in off or a dark state. However, at time T5 when the power is restored, the gaseous discharge lamp will not restrike immediately, but there is a very high voltage (approximately 250 volts) across it. Normally, the high voltage should cause the negative voltage feeding the gate of the SCR to be much greater than the positive bias voltage and should turn the SCR off. Howeventhe voltage from the transformer is now greater than the breakdown voltage of the unidirectional switch 78 and causes it to breakdown and go into its avalanche mode of operation whereby only a low voltage can be supported across it. Thus, there will only'be a low negative voltage feeding the gate of the SCR 70 and the positive bias voltage from resistor 72 will in fact control the SCR. This keeps the SCR in a conducting state and causes auxiliary lamp 68 to remain on.
The various resistors in the circuit are set at specific values to proportionately relate the voltage across the gaseous discharge lamp to appropriate voltages for the various circuit elements such as the SCR 70 and the unidirectional switch device 78. It is to be noted, while generally SCR circuits are triggered by a pulse, the present circuit does not use a trigger pulse but rather a constant DC bias on the gate. When using a trigger pulse the appropriate timing of the trigger pulse is of critical importance. In the present case, however, such timing is not necessary since the constant DC bias on the gate no longer makes the timing a critical factor.
When the auxiliary light is no longer required. the DC bias is simply removed and the lamp cxtinguishes.
it is therefore seen that in the present invention a single switch element is used to detect both the very low voltage during the warmup period of the gas discharge lamp to turn the auxiliary lamp on, as well as the very high voltage after a power interruption to turn the auxiliary lamp on. No electromechanical relays are employed and no additional parallel circuitry is necessary to shortout or disconnect the main switch element by means of a secondary switching element. In addition, no special ballasts are required for operation in connection with the circuit. In each case, the single switching element is biased to keep the suxiliary lamp on and the gaseous discharge lamp voltage is used to provide a voltage opposite to the biasing voltage to turn off the auxiliary lamp during normal operation of the gaseous discharge lamp.
While the present invention has been described with reference to particular embodiments thereof. it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention.
What is claimed is:
1. An auxilairy lighting system for use with a primary lighting system having a gaseous discharge lamp and a ballast connecting the gaseous discharge lamp to an alternating current source of voltage for igniting and operating said gaseous discharge lamp, said auxiliary lighting system comprising:
a. an auxiliary light source;
b. switch means connected in series with said auxiliary light source and an output from a ballast;
c. said switch means comprising an SCR and a bridge rectifier;
d. biasing means connected in series with said switch means and said auxiliary light source for producing an output'voltage acting on said switch means and maintaining said switch means in a conductive condition;
c. said biasing means including a resistor connected between a gate electrode of said SCR and a source of positive voltage; and
f. control means responsive to a voltage across the discharge lamp for producing an output proportional to said lamp voltage and opposing the output voltage of the biasing means;
g. said control means includes a transformer and a rectifier connected across a gaseous discharge lamp for producing a negative output voltage proportional to the voltage applied to said discharge lamp;
h. said output voltage from the transformer and rectifier being connected to the gate electrode of the SCR;
i. said control means having an output voltage which is greater in magnitude than said output voltage from the biasing means during a period of time when said gaseous discharge lamp is operating at full illumination and said SCR is in a nonconductive condition, and causing said SCR to become conductive in response to application of a starting voltage to said gaseous discharge lamp;
j. said control means also including a filter circuit and a breakdown device connected between the output of the transformer and the rectifier and the gate electrode of the SCR;
k. said breakdown device producing a fixed low voltage after application of a high voltage thereto in response to the application of a starting voltage to the discharge lamp.
2. An auxiliary lighting system as defined in claim 1,
a. the bridge rectifier is connected to the alternating current source of voltage and produces a positive voltage applied at the resistor of the biasing means;
3. An auxiliary lighting system as defined in claim 1,
a. said transformer has a primary connected across the gaseous discharge lamp and a secondary having ends interconnected at a first terminal;
b. said secondary having an intermediate tap providing a second terminal;
c. said filter circuit comprising capacitors and resistlamp and to a source of alternating current voltage for igniting and operating said discharge lamp;
0. an auxiliary light source; 7
d. rectifier means connected across said gaseous discharge lamp;
c. said rectifier means producing an output;
f. reed switch means comprising an electromagnetic coil enclosing a pair of movable contact elements;
g. said electromagnetic coil being connected to the output from said rectifier means in parallel with a filter capacitor;
h. said movable contact elements being connected in series with a limiting resistor between an anode and a gate electrode of a semi-conductor switch;
i. said contact elements when closed supplying a voltage to said gate electrode and causing said semiconductor switch to become conductive; and
j. permanent magnet means positioned adjacent said electromagnetic coil and acting on the movable contact elements to hold the contacts closed;
k. said electromagnetic coil when energized producing a magnetic field in opposition to the magnetic field of the permanent magnet;
I. said coil and said permanent magnet having a net field holding the contacts in engagement after a power interruption and during a warm-up period of the lamp;
m. said net field permitting the contacts to separate under conditions when the lamp is operating and producing an acceptable level of illumination. l= l =l l =l= a UNIT D STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. I 3, 87 3; 882 Dated March 25, 1975 Inventor(s) I Bernard J. Gershen It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 2, line '35, change -1amp (second instance) to --well--.
Column 5, line 60, change "sufficient" to -'-insufficient--.
Signed and sealed this 20th day of May 1975.
(SEAL) Att St:
e C. MARSHALL DANN RUTH c. MASON Commissioner of Patents Attesting Officer and Trademarks FORM (9459) USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE 2 I959 O--3fi6-33l,