Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TECZINIGAL FIELD AND PRiOR ART
.
This invention relates, in general, to warning systerns for
emergency vehicles alld, in particular, to an improved warning system
ernploying one or more flash tubes being tri~gered to produce two or
more light flashes in rapid succession.
More specifically, but Arithout restriction to the particular use
which is shown and described, this invention relates to a warning system
havirlg olle or more flash tubes which are flashed in rapid succession
for ~ duration of ~pproximately 30-90 milliseconds for greatly improving
0 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 obse~ver.
It is a well~nown objective in warning ~ystems to direct a
warning li~ht 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 warnirlg light producing a brief, but highly
intense flash. G;enerally, strobe lights are gas filled tubes which may
produce brief fk~shes having a dur{3tion of around 200 microseconds.
Despite the capability of known flash tube designs to produce a highly
intense ~sh, pri~r 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 l50 milliseconds, a duratioll 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 stimul~tes the eye of the observer has fln
ef~ect on the perceived brightness of light seen. 1'his condition has
become known as the Broca-Sulzer effect and demonstrRtes 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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laboratory instrument.
Subsequent studies have confirmed lhe Broca-Sulzer fllndings. In
one paper by M. S. Kat~, Vision Res., Yolume ~, Pages 361-373,
Pergamon Press 1964, and adaptation of several curYes from the Broca
and Sulzer papers dramaticaLly demonstrated the results of the
E3roca-Sulzer efEect. It was shown that a brief elash duration of .05
seconds for 170 lux flash appears to the human eyes five to six times
brighter than a steady 170 lux light. ThusJ hi~h 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, a fter which intervaI 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 su~cession to irnprove 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 ~ frequency higher than the
flicker fusion frQquency.
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 irnpro~ed flash tube
25 systern taking advantage of the Broca-Sulzer effect in a rnanner that
enhanced brightness of fl~sh is attained by increased awareness of a
warning light by an observer. The invention of the flpplication uses
two or more flflshes in rapid succession generated by a flash tube
having a flash duration o E 3U-90 milliseconds to conform to the
30 Broca-Sul~er effect. TIle 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 illumination9 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
35 frequency", the two ~lashes appear as a single flash. Thus, the
im~ention of the application is capable of attaining a greater
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perceptible brightness using a standard flash tube than
is possible in prior art devices using either multiple pulse
light flashes or moving reflectors.
Specifically, the invention relates to a multiple
flash strobe warning light system comprising, in combination,
flash lamp means, and circuit means coupled to the flash
lamp means for producing first and second flashes of light
at a critical predetermined interval so as to create the
appearance of a single flash and also greatly improve the
perception of brightness, the circuit means producing the
first and second flashes at an interval of between 30 and
90 milliseconds.
In its method aspect the invention relates to
a method of enhancing the perception of brightness of a
strobe warning light comprising the steps of producing first
and second light flashes having a critical time interval
of between 30 and 90 milliseconds so as to create the
appearance of a single flash having a duration equal to
the time interval.
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 per-
ceived brightness is attained of up to 5-6 times. Although
many similar circuits and arrangements may be employed, the
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clrcuit 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 utili~e 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 a~pears
to be approximately 5-6 times as bright as a liyht 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.
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Referring to ~igure 1 of the drawings~ flash lamp 10 is shown
therein comprising a flash tube 12, a trans~rmer 14, and a capacitor
16 mounted in conjunction with a contac$ base and body portion ~n~t
shown).
Flash tube 12 may eomprise a conventional Flash tube ha~ring 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 e~tends from metal trigger
band (not shown). Although no limitation is intended, flash ~ube 12
10 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 ~S-1062 transformer. Capacitor 16 is preferably a disc
ceramic capacitor and although no limitation is intended, capacitor 16
15 may comprise a Sprague 5CAS-S10 capacitor.
Electrical leRd 30 couples anode 20 to le~d 32 of capacitor 16,
while lead 34 of capacitor 16 is connected to one side 36 of
transforrner primary 38. Lead 4n connects the other side of
transformer primary ~0 to the ground contas~t of lamp 10 and to one
20 side of the transformer secondary 4~, while leud 44 connects trigger
electro~e 26 to the other side of the transformer secondary 48. Lead
45 connects the latter elements to the ground of the power supply
psl.
The cathodes of a pair of silicon controlled rectiiers SCR1 and
25 SCR2 are connected together by electrical leads 46 and 48 extending
from lead 30. The anodes of SCR1 and SCR2 are respectively
conneeted to a power supply PSI through leads 50 nnd 52 having diodes
CRl and CR2 in series with SCKI and SC:R2. Flash capacitors Cl and
C2, respectively, are connected between lead 50 and 52; and lead 45 by
30 leads 54a, b and 56 a, b. The gates 60 and 62 of SC:R1 and SCR2 are
each connected to a timing circuit G4 through transformer 66. T~le
timing circuit 64 can comprise any suitable device SUCIl as the timer of
National Semiconductor, Model LM555.
In operation, the power supply PS1 charges capacitor Cl and C2
35 to lhe desired energy level through diodes CR1 and C:R~ during a time
intervel, tl. At the end of time tl, a positive going edge occurs on
1~ ~ 1l'~2 ~ O
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terminal 1 of the tin ing circuit 64 causing SCR1 to conduct. When
SCR1 goes into conduction, a positive pulse appears on the trigger
cap~citor lfi causing fl~sh tube 12 to fire, discharging capacitor Cl~
After time t2 (the Broca-Sulzer interval), a negative gGing edge occurs
5 Oll terminal 1 of the timing circuit 1g. causing SCR2 to conduct. Flash
tube 12 atgain fires discharging capacitor C2. G~pacitors Cl and C2
discharge in approximately 2 milliseconds, thereby limiting the minimum
Yalue of time interval t2.
For purposes of illustration, a timing graph is shown providillg
10 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, tl and t2, may be employed, by which the flash tube 12 is
fLashed sequentially within an interval equal to the critical ranges oî
approximately 30-90 milliseconds in accordetnce with the invention,
15 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 Cl and C2 may be
charged to a voltetge of 450 volts through diodes CR1 etnd CR2. The
circuit then applies as voltage across capacitor 16 of 450 volts for a
20 period to produce ltwo successive flashes of about 2 milliseconds spaced
by a time period OI abo-ut 75 milliseconds within the critical range. The
flashes then occur a$ a frequency greater than "flicker fusion
frequency" to appear as a single flash OI light having a duration of 75
milliseconds and perceived brightness of 5-6 tirnes normetl brightness
25 and, thus, increased warning light conspicuity.
It should be apparent that the flash la mp 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
30 flashing a strobe light for more than two successive ~lashes as long AS
tile time between flashes is within the separation Or 30-90 milliseconds.
While the in~rention has been described Witil 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
35 for elements thereof without departing from the scope of the
invention. In addition, many modifications may be made to adapt a
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particular situation or material to the teachings o~ the invention
without departing from the essential scope thereof. ~herefore, it is
intended that the invention not be limited to the particul~r embodiment
disclosed as the best mode contemplated ~or carrying out this
5 invesltion, but that the invention will include all embodiMents ~alling
within the scope of the appended claims.
