WO1985000950A1

WO1985000950A1 - Flash tube employing multiple flashes

Info

Publication number: WO1985000950A1
Application number: PCT/US1984/001129
Authority: WO
Inventors: Michael V. Mcconnell; Frederick W. Eggers
Original assignee: Federal Signal Corporation
Priority date: 1983-08-16
Filing date: 1984-07-18
Publication date: 1985-02-28
Also published as: KR890003061B1; EP0153345A1; JPS61500086A; GB2155710B; GB8506902D0; GB2155710A; CA1235210A; EP0153345A4; KR850001654A

Abstract

A warning system for emergency vehicles having one or more flash tubes (12) which are flashed in rapid succession during an interval of 30-90 milliseconds to appear as a single flash. A pair of silicon controlled rectifiers (60, 62) are rendered successively conductive to discharge a pair of capacitors (C1, C2) for causing the flashes of the flash tube. The interval between the conduction periods of the silicon controlled rectifiers is controlled by a timer device (64).

Description

FLASH TUBE EMPLOYING MULTIPLE FLASHES TECHNICAL FIELD AND PRIOR ART This invention relates, in general, to warning systems for emergency vehicles and, in particular, to an improved warning system employing one or more flash tubes being triggered to produce two or more light flashes in rapid succession.

More specifically, but without restriction to the particular use which is shown and described, this invention relates to a warning system having one or more flash tubes which are flashed in rapid succession for a duration of approximately 30-90 milliseconds for greatly improving the perception of brightness and the warning light conspicuity. Because the two or more light flashes are closely spaced, they appear as a single flash of light to the observer.

It is a well-known objective in warning systems to direct a warning light in a manner to be optimumly conspicuous to as many observers as possible in a given area. A flash tube has been found to be a greatly effective warning light producing a brief, but highly intense flash. Generally, strobe lights are gas filled tubes which may produce brief flashes having a duration of around 200 microseconds.

Despite the capability of known flash tube designs to produce a highly intense flash, prior techniques have failed to be able to increase their perception of brightness in an effective and readily attainable manner.

In the past, brief flashes of a flash tube have been generated in succession in an attempt to enhance the conspicuity of the warning lights. These systems have failed to significantly increase brightness because the interval between flashes did not affect perceived brightness in any significant manner. It is common in the prior art to utilize two flashes spaced by approximately 150 milliseconds, a duration far longer than the critical interval discovered in conjunction with the invention of the application. In 1902, the subject of brief flash brightness was discussed in a series of papers by Broca and Sulzer in which it was observed that the time during which light stimulates the eye of the observer has an effect on the perceived brightness of light seen. This condition has become known as the Broca-Sulzer effect and demonstrates that there is a critical flash duration at which light flashes appear to the observer to be brighter than may be otherwise measured by a

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OMPI laboratory instrument.

Subsequent studies have confirmed the Broca-Sulzer findings. In one paper by M. S. Katz, Vision Res., Volume 4, Pages 361-373, Pergamon Press 1964, and adaptation of several curves from the Broca and Sulzer papers dramatically demonstrated the results of the Broca-Sulzer effect. It was shown that a brief flash duration of .05 seconds for 170 lux flash appears to the human eyes five to six times brighter than a steady 170 lux light. Thus, high intensity light can be made to appear more intense and brighter if two flashes of light are flashed at a critical range of short duration, after which interval the light loses its appearance of enhanced brightness.

It is therefore an object of this invention to use two or more flashes of light in rapid succession to improve perception of brightness.

Another object of this invention is to create two or more strobe flashes at the Broca-Sulzer duration to enhance appearance of brightness and warning light conspicuity.

It is further an object of this invention to drive a flash tube to produce two or more successive flashes at a frequency higher than the flicker fusion frequency. Still another object of this invention is to enhance apparent brightness of a warning system and to create more visible light to the observers.

These and other objects are attained in accordance with the present invention wherein there is provided an improved flash tube system taking advantage of the Broca-Sulzer effect in a manner that enhanced brightness of flash is attained by increased awareness of a warning light by an observer. The invention of the application uses two or more flashes in rapid succession generated by a flash tube having a flash duration of 30-90 milliseconds to conform to the Broca-Sulzer effect. The two flashes create an apparent brightness in accordance with the present invention of 5-6 times what is possible with a steady light of similar illumination, because the time interval between the two or more pulses is within a critical range. Because the frequency of the flashes is higher than the so-called "flicker fusion frequency", the two flashes appear as a single flash. Thus, the invention of the application is capable of attaining a greater perceptible brightness using a standard flash tube than is possible in prior art devices using either multiple pulse light flashes or moving reflectors.

BRIEF DESCRIPTION OF THE DRAWINGS A further object of the invention, together with additional features contributing thereto and advantages accruing therefrom, will be apparent from the following description of a preferred embodiment of the invention which is shown in the accompanying drawing with like reference numerals indicating corresponding parts throughout, wherein: Figure 1 is an electrical circuit diagram of one embodiment of the invention of the application for a double flash flash tube; and

Figure 2 is a timing chart showing representative operation of the circuit of Figure 1.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT

In the following description, there is illustrated an embodiment of the circuit and method for operating one or more flash tubes in a manner that an enhancement of perceived brightness is attained of. up to 5-6 times. Although many similar circuits and arrangements may be employed, the circuit shown in Figure 1 is illustrative of one technique of attaining the objects of the invention. It is within the scope of the invention to utilize other circuits and systems to attain the improved results of the invention, such that two or more brief flashes produced by a flash tube are created during a selected time interval for enhanced brightness appearing as a single flash.

In accordance with the invention as provided by the circuit of Figure 1, the flash tube of Figure 1 is arranged to create two or more flashes spaced by successive intervals of 30-90 milliseconds. It is found that a warning light system employing the technique in the invention appears to be approximately 5-6 times as bright as a light of equal lumens having a steady output, dependent on the magnitude of the duration in the approximate range of 30-90 milliseconds. Because the flashes from the flash tube of the invention are so closely spaced, they appear as a single flash of light having a duration approximately equal to intervals between flashes. Referring to Figure 1 of the drawings, flash lamp 10 is shown therein comprising a flash tube 12, a transformer 14, and a capacitor 16 mounted in conjunction with a contact base and body portion (not shown). Flash tube 12 may comprise a conventional flash tube having a first electrode 20 which, for convenience, will be designated an anode; a second electrode 22 which, for convenience, will be designated a cathode; and a trigger electrode 24 which extends from metal trigger band (not shown). Although no limitation is intended, flash tube 12 may be General Electric Model FT-106C.

Transformer 14 is generally a miniature transformer and although no limitation is intended, transformer 14 may comprise a Siemens ZS-1062 transformer. Capacitor 16 is preferably a disc ceramic capacitor and although no limitation is intended, capacitor 16 may comprise a Sprague 5GAS-S10 capacitor.

Electrical lead 30 couples anode 20 to lead 32 of capacitor 16, while lead 34 of capacitor 16 is connected to one side 36 of transformer primary 38. Lead 40 connects the other side of transformer primary 40 to the ground contact of lamp 10 and to one side of the transformer secondary 42, while lead 44 connects trigger electrode 26 to the other side of the transformer secondary 48. Lead 45 connects the latter elements to the ground of the power supply PSx.

The cathodes of a pair of silicon controlled rectifiers SCRi and SCR2 are connected together by electrical leads 46 and 48 extending from lead 30. The anodes of SCRi and SCR are respectively connected to a power supply PS through leads 50 and 52 having diodes CRi and CR2 in series with SCRi and SCR2. Flash capacitors Ci and C2, respectively, are connected between lead 50 and 52; and lead 45 by leads 54a, b and 56 a, b. The gates 60 and 62 of SCRi ^and SCR2 are each connected to a timing circuit 64 through transformer 66. The timing circuit 64 can comprise any suitable device such as the timer of National Semiconductor, Model LM555.

In operation, the power supply PSi charges capacitor Ci and C2 to the desired energy level through diodes CRi and CR2 during a time interval, tj. At the end of time ti, a positive going edge occurs on terminal 1 of the timing circuit 64 causing SCRi ^to conduct. When SCRi goes into conduction, a positive pulse appears on the trigger capacitor 16 causing flash tube 12 to fire, discharging capacitor C - After time t2 (the Broca-Sulzer interval), a negative going edge occurs on terminal 1 of the timing circuit 14 causing SCR2 to conduct. Flash tube 12 again fires discharging capacitor C2. Capacitors C and C2 discharge in approximately 2 milliseconds, thereby limiting the minimum value of time interval t2«

For purposes of illustration, a timing graph is shown providing an example of energy levels and time intervals provided by the circuit of Figure 1. It should be understood that other energy levels and time intervals, ti and t2, may be employed, by which the flash tube 12 is flashed sequentially within an interval equal to the critical ranges of approximately 30-90 milliseconds in accordance with the invention, where optimum brightness generally occurs in the mid portion of this range. In Figure 2, timer 64 produces an output of 5 volts during interval t2 of 75 milliseconds. Both capacitors Ci and C2 may be charged to a voltage of 450 volts through diodes CRi and CR2. The circuit then applies as voltage across capacitor 16 of 450 volts for a period to produce two successive flashes of about 2 milliseconds spaced by a time period of about 75 milliseconds within the critical range. The flashes then occur at a frequency greater than "flicker fusion frequency" to appear as a single flash of light having a duration of 75 milliseconds and perceived brightness of 5-6 times normal brightness and, thus, increased warning light conspicuity.

It should be apparent that the flash lamp 12, operated in accordance with the invention, may be used with other similar flash lamps in a warning system of any appropriate design. The invention herein disclosed may also accomplish the objects of invention by flashing a strobe light for more than two successive flashes as long as the time between flashes is within the separation of 30-90 milliseconds.

While the invention has been described with reference to the preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A flash lamp system comprising flash lamp means; circuit means coupled to said lamp means triggering flash for flashes of light of short duration; and said circuit means including means for causing said flash lamp means to trigger at least two successive flashes during a time interval of approximately 30-90 milliseconds.

2. The flash lamp system according to Claim 1 wherein said flash lamp means has a flash tube with an anode, a cathode and a trigger electrode.

3. The flash lamp system according to Claim 1 wherein said circuit means includes timer means for triggering said successive flashes.

4. The flash lamp system according to Claim 1 wherein said circuit means includes a pair of capacitors connected to said flash lamp, said capacitors being successively discharged to trigger said successive flashes.

5. The flash lamp system according to Claim 4 wherein said circuit means further includes a pair of silicon controlled rectifiers respectively connected to said capacitors, said rectifiers becoming successively conductive to discharge said capacitors on a successive basis.

6. The flash lamp system according to Claim 5 wherein said circuit means includes timer means for controlling the conductive periods of said rectifiers.

7. A flash lamp comprising a flash lamp having a flash tube for producing flashes of light; and

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OM means coupled to flash lamp for producing two or more successive flashes of light during a time interval of approximately 30-90 milliseconds.

8. The flash lamp according to Claim 7 wherein said successive flashes appear as a single flash.

9. The flash lamp according to Claim 7 further comprising circuit means for producing a series of two or more of said successive flashes.

10. A method of enhancing the appearance of brightness of a flash tube comprising the steps of producing flashes of light of a short duration from a flash tube and causing some of said flashes of light to be flashed as two or more successive flashes during intervals of approximately 30-90 milliseconds between successive flashes.

11. The method according to Claim 10 including the step of generating said successive flashes at equal intensity of brief duration.