Photoflash lamp including improved ignition means

An electrically-activated, subminiature photoflash lamp including a glass envelope, a quantity of combustible shred material (e.g., zirconium or hafnium) for providing high intensity light output upon ignition thereof, and an ignition means for igniting the combustible upon application of a suitable pulse such as typically provided by a piezoelectric element utilized in many of today's pocket-type cameras. The ignition means includes a first quantity of primer material located within a buttom of the lamp's envelope, a pair of lead-in wires secured within the bottom end of the envelope and in electrical contact with the primer, and a thin member located at an opposite end of the envelope from the first primer and having thereon a second quantity of primer material. The first primer, when ignited, thus serves to ignite a first end portion of the combustible shred material while substantially simultaneously igniting the spaced, second primer. This second primer in turn ignites the opposing end portion of the shred material such that this material burns from the opposing ends thereof toward the center to in turn assure both uniformity of burn and an accelerated rate thereof. In one example, the thin member comprised a cylindrical-shaped mica disk.

DESCRIPTION 
TECHNICAL FIELD 
The present invention relates to photoflash lamps and particularly to 
photoflash lamps which are electrically activated. Even more particularly, 
the invention relates to improved means for igniting such lamps. 
BACKGROUND 
Lamps of the above type are generally classified into two varieties: 
low-voltage and high-voltage. Low-voltage photoflash lamps typically 
include a glass envelope with a combustion-supporting gas (e.g., oxygen) 
and a quantity of filamentary, combustible material (e.g., shredded 
hafnium or zirconium) therein. A pair of electrically conductive lead 
wires are usually sealed in one end of the envelope and extend therein. A 
filament is utilized and interconnects the extending ends of the wires. 
When the filament is heated by a firing current usually generated from a 
low-voltage source such as battery or charged capacitor (e.g., having a 
voltage of from about 1.5 to 15 volts), it ignites a primer material which 
then ignites the combustible material to produce a flash of light. 
Naturally, the oxygen gas aids in the above ignition. In high-voltage 
lamps, the use of a filament is usually excluded by the provision of a 
glass or ceramic bead in which are located the extending ends of the 
lamp's conducting wires. The combustible-igniting primer material serves 
to bridge the portions of these ends which project through the bead. 
High-voltage lamps also include the aforedescribed filamentary material 
and combustion-supporting gas. Flashing is accomplished by a firing pulse 
approaching a few thousand volts and usually provided by a piezoelectric 
element. In another type of high-voltage lamp, the primer is located 
within an indentation in the bottom of the lamp and the conductive wires 
extend therein. 
The teachings of the instant invention are particularly concerned with high 
voltage lamps, although it will be understood from the following that said 
teachings may be readily extended to lamps of the earlier generation, low 
voltage variety. Even more particularly, the teachings as provided herein 
are especially concerned with high voltage lamps wherein the primer 
material is located in the bottom of the lamp (e.g., along a bottom 
surface thereof). 
Locating the lamp's primer material within a recess, cavity, indentation, 
etc. at the bottom end (that containing the lamp's two lead-in wires) of 
the envelope is particularly desirable in photoflash lamps of the 
subminiature variety (e.g., those having an internal volume of less than 
about 0.2 cubic centimeters) in view of the relatively large space 
required for occupancy by the lead-in wires which form part of the lamp's 
ignition structure (the primer material typically forming the remaining 
part). While this arrangement allows for the saving of precious internal 
volume of the lamp's envelope to thereby enable relatively larger volumes 
of shredded combustible therein, uniform ignition of the combustible 
shreds can prove somewhat difficult in that the shred mass typically burns 
from one end of the envelope to the other when ignited. Accordingly, 
various factors such as extent of compaction and final shred mass location 
can adversely affect the combustion rate of this mass. This in turn can 
adversely alter (e.g., extend) the peak output time for the ignited lamp 
as well as the total light output. With particular regard to peak output 
time, it is understood that this parameter is critical in view of the 
requirement that the lamp's peak output must coincide with the shutter 
operation of the corresponding camera utilizing a photoflash lamp of this 
variety. 
The present invention, as will be defined, describes a photoflash lamp 
including a novel means of ignition for the lamp's shredded combustible 
material such that the combustion rate of this material is substantially 
increased. The invention also enables the shredded combustible material to 
burn in a substantially more uniform manner than typical photoflash lamps 
of the prior art. Although the teachings as provided herein are 
particularly adaptable to photoflash lamps of the electrically-activated, 
subminiature variety, it is understood that these teachings are also 
applicable to other varieties of high voltage photoflash lamps, including 
those containing the aforementioned ignition structure wherein a glass 
support bead or similar component is also used. 
It is believed, therefore, that a photoflash lamp possessing the unique 
features as stated above would constitute a significant advancement in the 
art. 
DISCLOSURE OF THE INVENTION 
It is a primary object of the present invention to provide an 
electrically-activated photoflash lamp wherein ignition of the combustible 
material therein is accomplished at a substantially increased rate over 
typical photoflash lamps of the prior art and wherein the combustible 
material burns substantially more uniformly than said prior art lamps. 
It is also another object of the present invention to provide a photoflash 
lamp possessing the aforementioned advantageous features yet which can be 
readily produced on a mass production basis and therefore at relatively 
low cost. 
In accordance with one aspect of the invention, there is provided a 
photoflash lamp comprising an elongated, light-transmitting envelope, a 
quantity of combustible, light-producing material located within the 
envelope, and an ignition means for igniting the combustible, said 
ignition means including a first quantity of primer material located 
within a first end of the envelope adjacent part of the combustible 
material for igniting this part upon ignition thereof, a pair of lead-in 
wires secured within the envelope and connected electrically to the first 
primer for providing ignition thereof upon application of a suitable pulse 
(e.g., such as provided by a typical piezoelectric element presently 
utilized in the art) across the lead-in wires, a thin member oriented at 
an opposing end of the envelope from the first primer and having 
positioned thereon a second quantity of primer material adjacent a second 
part of the combustible material for igniting said second part upon being 
ignited by the first primer material.

BEST MODE FOR CARRYING OUT THE INVENTION 
For a better understanding of the present invention, together with other 
and further objects, advantages, and capabilities thereof, reference is 
made to the following disclosure and appended claims in connection with 
the above-described drawings. 
With particular attention to FIG. 1, there is shown a photoflash lamp 10 in 
accordance with a preferred embodiment of the invention. Lamp 10 comprises 
an elongated, light-transmitting envelope 11, a quantity of combustible, 
light-producing material 13 positioned within the envelope, and an 
ignition means 15 for igniting the combustible 13. Envelope 11 is 
preferably of glass (e.g., lime glass), but may also be of a suitable 
plastic or similar insulative material. By the term light-transmitting is 
meant any material which permits passage of the high intensity light as 
typically provided from a photoflash lamp therethrough without 
substantially altering said output. Envelope 11, in cross-section, is 
preferably of substantially cylindrical configuration having an external 
diameter of about 0.210 inch. Each of the longitudinal side walls 17 of 
the envelope possess a thickness of about 0.020 inch. The total internal 
volume of envelope 11 is somewhat less than about 0.200 cubic centimeter, 
specifically, about 0.175 cubic centimeter. As stated, envelope 11 is of 
substantially elongated shape. In one specific example, the finished 
envelope (as shown in FIG. 1) possessed a total length of about 0.650 
inch. This length understandably is about three times the envelope's 
external diameter. 
Combustible, light-producing material 13 is preferably zirconium or hafnium 
and more preferably of shredded configuration. That is, material 13 is 
comprised of several individual shreds of the stated metal wherein these 
shreds are sheared from a sheet of thin foil. Use of shredded combustible 
material of the variety described is well known in the art and further 
description is not believed necessary. In one example of the invention, a 
total of approximately 12 milligrams of zirconium shreds was utilized 
within the lamp vessel. 
Ignition means 15 comprises a first quantity of primer material 19 located 
within a first, bottom end 21 of envelope 11. As shown, first primer 
material 19 is positioned along the bottom wall 23 of end 21. In one 
example, a total of from about 0.500 to about 0.750 milligrams of primer 
was used. First primer material 19 comprised a mixture of about 80 percent 
by weight zirconium and about 20 percent by weight potassium perchlorate. 
With regard to the invention, it is to be understood that other materials 
such as are known in the art may be utilized. It is also within the scope 
of the invention to modify the percentages of those materials as defined 
without adversely affecting the performance of the invention. As shown in 
FIG. 1, ignition means 15 further includes a pair of lead-in wires 25 
which are secured within the bottom end of envelope 11 in electrical 
contact with the first primer material 19. Sealing of each of the lead-in 
wires 25 can be accomplished using techniques well known in the art and 
further description is therefore not believed necessary. Each wire 25 is 
preferably of a nickel-iron alloy and possesses an external diameter of 
about 0.015 inch. Wires 25 are spaced apart within the bottom end 21 of 
envelope 11 a total distance of about 0.040 inch. Application of a 
suitable pulse (such as a high voltage, low energy pulse as provided by a 
piezoelectric element typically utilized in many of today's pocket-type 
cameras) results in generation of a spark between the ends of each wire 
which are in contact with first primer material 19. Passage of this spark 
through the first primer material 19 results in ignition thereof to in 
turn ignite the portion of the shredded combustible material 13 located 
immediately adjacent primer material 19. As shown, the end portions of 
lead-in wires 25 which contact primer material 19 are flush with interior 
surface 23. 
In accordance with the unique teachings herein, ignition means 15 further 
comprises a second quantity of primer material 19' which is located on a 
thin member 27 which in turn is positioned at an opposing, second end of 
envelope 11 from the aforedefined bottom, sealed end 21. In one example of 
the invention, the second primer material 19' was of the same composition 
as that of first quantity 19. A similar amount (weight) was also utilized. 
As shown in FIG. 1, the second quantity of primer material is positioned 
immediately adjacent (and in physical contact with) the shredded 
combustible 13 but on an opposing end (31) thereof from the first quantity 
19. This material, when ignited by the first primer material 19, in turn 
serves to ignite the portion of shredded combustible located adjacent 
thereto. It can be seen, therefor, that first primer 19 almost 
simultaneously serves to ignite the lowermost portion of shredded 
combustible as well as the spaced, second quantity of primer material 19'. 
The second quantity in turn almost instantly serves to ignite the 
opposing, non-ignited portion of combustible material 13 such that this 
material burns from opposing ends thereof toward the center and therefor 
at an accelerated rate over ignition means as typically found in the prior 
art. This results in an advantageous earlier peak output (see FIG. 2) over 
a similar lamp not including a second quantity of primer material in the 
arrangement depicted in FIG. 1. The relative light output (in footcandles) 
in comparison to the output time (in milliseconds) for the invention is 
represented by the curve "I". The corresponding relative light output of a 
similar electrically-activated photoflash lamp not possessing a second 
primer is represented by the dashed curve "P". In making these 
comparisons, similar quantities of shredded combustible and first primer 
material were utilized. In addition, each of the glass envelopes used 
possessed the same internal volume. It can be readily seen from the graph 
in FIG. 2. that the relative light output of the instant invention peaks 
at a substantially earlier period from that of the control model. In 
addition, photographic prints as produced from cameras utilizing the 
invention typically possessed fewer, if any, "hot spots" than prints 
exposed using photoflash lamps such as the control model described above, 
thus indicating that the resulting light output from the invention is more 
uniformly distributed over the subject matter being illuminated during 
exposure of the print negatives. 
The thin member 27 used in the invention comprises a substantially 
cylindrical 0.002 inch thick mica disk having an external diameter of 
about 0.160 inch. Because this external diameter was about 0.010 inch less 
than the corresponding internal diameter for the cylindrical envelope 11, 
disk 27 was substantially loosely positioned atop combustible material 13. 
The disk was also prevented from upward displacement by the tipped, 
opposing second end portion 31 of envelope 11. In producing the invention, 
it is understood that the tipped end 31 is achieved subsequent to 
insertion of disk 27 and the corresponding second primer 19' within the 
open second end of the glass tubing which eventually constitutes envelope 
11. The first quantity of primer 19 and shredded combustible 13 are 
previously positioned within this open end, said positioning occuring 
after the aforementioned sealing of the two lead-in wires 25 within first 
end 21. Tipping of the glass tubing to provide end 31 can be accomplished 
using techniques known in the photoflash lamp art. One distinct advantage 
of the instant invention is that utilization of disk 27 substantially 
eliminates the possibility of combustible shred material being captured 
within tip portion 31 during sealing thereof, a common occurrence when 
tip-sealing subminiature lamp envelopes. Shred material within the second 
end can adversely affect the seal formed thereat. Understandably, 
positioning of disk 27 prior to forming the second sealing operation 
forces substantially all of the shred material downwardly within envelope 
11, thus preventing the above undesirable occurrence. 
It is within the scope of the invention to utilize a material other than 
mica for disk 27. For example, it is possible to use an aluminum disk with 
equal success, said disk possessing substantially the same configuration 
and dimensions described above. It is also within the scope of the 
invention to provide a disk of a different configuration than stated, 
suitable examples being either square or rectangular. A cylindrical 
configuration is preferred when a corresponding cylindrical-shaped glass 
envelope is employed. It is even further within the scope of the invention 
to frictionally insert the primered disk 27 within envelope 11 to provide 
a more stationary means of positioning said component. This is not 
necessary in the invention, however, in that the primer and disk members 
can be loosely positioned as indicated. 
Thus there has been shown and described an electrically-activated 
photoflash lamp including a novel ignition means for providing accelerated 
ignition of the combustible shred material utilized in the lamp. The 
improved ignition means further assures more uniform burning of the 
combustible material to thus provide greater uniformity of output 
therefrom. 
While there have been shown and described what are at present considered 
the preferred embodiments of the invention, it will be obvious to those 
skilled in the art that various changes and modifications may be made 
therein without departing from the scope of the invention as defined by 
the appended claims.