US3067601A - Photoflash lamp - Google Patents

Description

Dec. 11, 1962 F. ANDERSON EI'AL 3,

PHOTOFLASH LAMP Original Filed Oct. 21, 1957 Fly 2 'zoossc.

MEGALUMENS M ILLISECONDS LESTER F ANDERSON WILLIAM C. FINK INVENTORS ATTORNE United States Patent Ofifice 3,067,601 Patented Dec. 11, 1962 3,067,601 PHOTOFLASH LAMP Lester F. Anderson and William C. Fink, Williamsport,

Pa., .assignors to Sylvania Electric Products Inc., a

corporation of Delaware Continuation of application Ser. No. 691,298, Oct. 21,

1957; This application Sept. 29, 1960, Ser. No. 59,358

12 Claims. (Cl. 67--31) This invention relates to photofiash lamps and more particularly to photofiash lamps in which zirconium is employed as the combustible.

In the manufacture of photofiash lamps, it has been the general commercial practice in recent years to employ aluminum foil shredded to filamentary form as the combustible and oxygen as the combustion-supporting gas, with the ratio between combustible and weight of gas maintained at or near stoichiometric balance. The lamp envelope is provided with an external, and, on large lamps, an internal coating as a safety precaution to prevent fragmentation, since the pressure during combustion rises to values many times initial pressure because the heat developed expands the oxygen gas. Over the years, increases in the total light output per unit volume of the lamp envelope have been made possible by the use of stronger lamp envelopes, stronger coatings, and improved techniques in the dispersion and distribution of the filamentary combustible in the lamp envelope.

Concurrently with the efforts to achieve higher levels of light output per unit volume has been an attempt to develop photofiash lamps having a color temperature that would be equivalent to daylight in order to give perfect balance when used with daylight color film. The color temperature of the aluminum-oxygen reaction is approximately 380.0 K. Since the color temperature of daylight plus skylight, for which daylight color film is balanced, is about 6000 K., it has been the usual practice to introduce a blue dye into the exterior lacquer coating on the lamp envelope to act as a filter, thus effectively raising the color temperature from about 3800" K. to about 6000" K. Absorption of light by the filter coating on an aluminum-filled lamp is about 55%.

Although, as pointed out above, increases in the total light output per unit volume of the lamp envelope of an aluminum-filled photofiash lamp have been obtained by the use of stronger lamp envelopes and/ or stronger coatings, we have found that when zirconium foil, preferably reactor grade, shredded to filamentary form, is employed as the combustible, a substantial increase in the total light output per unit volume of the lamp envelope is obtainable without the necessity for using stronger lamp envelopes and/ or stronger coatings. We have also found that the color temperature of a photofiash lamp provided with a combustible of filamentary zirconium is approximately 300" K. higher than the color temperature of a photofiash lamp provided with a combustible of filamentary aluminum, thus making it possible to reduce the absorption of the blue filter coating employed to raise the color temperature to about 6000 K.

Other advantages and features of the photofiash lamp of our invention will be pointed out in connection with the description of the accompanying drawings in which:

FiGURE l is a plot of light output in terms of megalumens against time in terms of milliseconds.

FIGURE 2 is a plot of various camera shutter speeds.

FIGURE 3 is an elevational view partly in section of a photofiash lamp.

Curve A in FIGURE 1 illustrated the light output characteristic of photofiash lamps known in the trade as M2s. The M2 lamps used in this test were provided with about 15 milligrams of aluminum foil shredded to filamentary form as the combustible and oxygen at about cms. Hg, as the combustion-supporting gas, with the ratio between combustible and weight of gas at or near stoichiometric balance. The lamp envelope employed was a T6/: bulb having a cubical content of about 7.5 cc.

Curve B in FIGURE 1 illustrates the light output characeristic of photofiash lamps provided with about 48 milligrams of zirconium foil shredded to filamentary form as the combustible and oxygen at about 130 cms. Hg, as the combustion-supporting gas, with the ratio between combustible and weight of gas at or near stoichiometric balance. The lamp envelope employed was a T6 /2 bulb having a cubical content of about 7.5 cc.

Curve C in FIGURE 1 illustrates the light output characteristic of photofiash lamps known in the trade as Press 25 's. The Press 25 lamps used in this test were provided with about 33 milligrams of aluminum foil shredded to filamentary form as the combustible and oxygen at about 53 cms. Hg, as the combustion-supporting gas, with the ratio between combustible and weight of gas at or near stoichiometric balance. The lamp envelope employed was a B12 bulb having a cubical content of about 31 cc.

The filamentary aluminum used as the combustible in the M2 lamps and the Press 25 lamps had cross sections of about 0.4 10 and 0.65 10 sq. in. respectively. The cross section of the filamentary zirconium used in the lamps of Curve B was about 1.2 l0- sq. in.; however, satisfactory results may be obtained with cross sections between about O.4 10- to about 1.8 10 sq. in.

The lamp envelopes used in the manufacture of the amps of Curves A and C, as well as the aluminum fill, oxygen pressure and other structural characteristics, are identical to those presently employed in the commercial manufacture of M2s and Press 25s. The initial gas fill pressures with which these lamps were provided were determined primarily by safety considerations. The instantaneous peak pressures on firing of these lamps are as close to the maximum pressures, which the lamp envelopes can withstand without danger of explosion, as is practical and still provide a reasonable factor of safety.

Turning now to FIGURE 1, it will be noted that Curve B, representing the zirconium lamp, is flatter than either Curve A or Curve C, representing the present commercial, filamentary aluminum-filled M2 and Press 25 respectively. Apparently, for the cross sections selected, the zirconium ignites very rapidly but radiates useful energy for a longer time compared to aluminum. These combined characteristics enhance the adaptability of the zirconium lamp for use with both high speed synchronization in the more expensive cameras and the relatively slow speed synchronization of the fixed focus box camera.

Camera shutter speeds of sec., sec., sec., and box camera speed are illustrated schematically in FIGURE 2. In order to determine the light output that camera film will actually see, it is necessary to integrate that portion of each of the curves in FIGURE 1 for which the shutter is open. It will be noted that the peak of Curve A, the M2 lamps, occurs several milliseconds ahead of the opening of the shutter of the high speed camera, and, therefore, M2 lamps cannot be used for high speed synchronization at all. The M2 is designed to peak early in order to give maximum light output for box cameras. its peak characteristic is too sharp and total light output too low to attempt to design the lamp for satisfactory synchronization on both high speed and box cameras.

Total integration of the lamps illustrated gives about 7200 lumen seconds for the M2 lamps, about 20,000 lumen seconds for the Press 25 lamps, and about 18,000 lumen seconds for the zirconium lamps.

For high speed synchronization, the following useful light outputs are obtained:

For the fixed focus box camera, assuming second Opening, the following useful light outputs are obtained:

Lamp: Lumen seconds M2 7,000 Press 25 12,000 Zirconium 13,000

Thus it can be seen that, at high speed synchronization, the small zirconium lamp is virtually the equivalent of the aluminum-filled Press 25. Since, as was noted above, the cubical content of the zirconium lamp used was about 7.5 cc., and the cubical content of the Press 25 lamp used was about 31 cc., the zirconium lamp gives substantially the same light output with one fourth the envelope volume.

As was mentioned above, the color temperature of the aluminum-oxygen reaction is about 3800 K., and a blue dye is usually introduced into the lacquer coating on the lamp envelope to act as a filter and thus effectively raise the color temperature to about 6000 K. Since the color temperature of the zirconium lamp is about 300 K. higher than the aluminum lamp, the absorption of the blue filter may be reduced, and thus make it possible to obtain a daylight rating of 9,000 lumen seconds for a zirconium-filled lamp in a lamp envelope of about 7.5 cc. volume, compared to a daylight rating of 8,000 lumen seconds for an aluminum-filled lamp in a lamp envelope of about 31 cc. volume. When pressures substantially higher than those mentioned in the description of FIG- URE 1 are used, lamp envelopes capable of withstanding the shock of very high instantaneous peak pressures on firing, such as those described in the co-pending application of Anderson et al., Serial No. 516,722, filed June 20, 1955, now US. Patent 2,865,186, should be employed.

It is possible to make a zirconium flash lamp as illustrated in FIGURE 1 because of the greater efficiency of combustion of zirconium compared to aluminum, and because of the lower peak instantaneous pressure that is developed in the zirconium lamp. For comparable envelopes using the same protective coatings, the zirconium lamp will remain intact upon flashing, where initial pressures are substantially higher than those for aluminum. In all these cases, the charge is in susbtantial stoichiometric balance. Peak pressures for comparable zirconium and aluminum lamps in the same type envelopes have been measured on a pressure transducer. At constant initial pressure, the instantaneous peak pressures developed in the aluminum lamps range from about 28% higher to as much as about 100% higher compared to zirconium lamps. Instantaneous peak pressures are approximately equal, viz., about 250 cms., for the com mercial M2 lamp having an initial pressure of about 95 cms. and the zirconium lamp, whose characteristic is illustrated in FIGURE 1, Curve B, having an initial pressure of about 130 cms. Thus the zirconium lamp is provided -with a gas filling at a pressure more than one-half of the pressure which the envelope can withstand safely upon firing whereas the gas filling with which the aluminum lamp is provided is at a pressure substantially less than one-half of the pressure which the envelope can withstand safely upon firing. The ratio of instantaneous peak pressure to initial fill pressure for the aluminum filled M2 lamp is about 2.6 to 1 whereas for the zirconium filled lamp it is only about 1.9 to 1. As the initial pressureis increase.

increased, the difference in instantaneous peak pressures between the two types of combustible also appears to This is a significant advantage in view of the fact that, up to certain high pressure regions, efliciency increases with increases in gas pressures, because it makes possible the use of higher initial pressures with less danger of fragmentation of the lamp envelope.

In addition to the features and advantages described above which characterize a photofiash lamp employing filamentary zirconium as the combustible, we have noted that faster and more reliable ignition maybe obtained from the low power battery sources used because the zirconium requires lower activation energy than aluminum and therefore can be ignited at lower temperatures. Although the problem of inadvertent ignition ofa photoflash lamp is always one to be reckoned with, we have also noted that filamentary zirconium is characterized by better conductivity compared to filamentary aluminum, which is always slightly oxidized. This makes possible more positive internal grounding and thus reduces susceptibility to ignition by static discharges or discharges occurring in a dynamic field such as radar.

Referring now to FIGURE 3, the photofiash lamp shown therein is, except for the combustible described above, a conventional, commercial photofiash lamp and thus will be described only briefly. It comprises a hermetically sealed, glass, light-transmitting envelope 2 provided with a filling of gas, such as oxygen, and filamentary zirconium. The envelope 2 is provided with a base 6 affixed to the neck thereof. A tungsten filament 8, the ends of which are attached to lead-in wires 10 and 12 is disposed within envelope 2. The inner ends of the lead-in wires 10 and 12 are provided with a quantity of ignition paste 14. The lead-in wires 10 and 12 are supported within envelope 2 by stem 16 and are connected to conventional base contacts in the usual manner. The outer wall of the lamp envelope is provided with a protective coating 18 to prevent fragmentation during firing of the lamp.

This application is a continuation of our co-pending application, Serial Number 691,298, filed October 21, 1957, entitled Photoflash Lamp, now abandoned.

What we claim is:

1. A photofiash lamp comprising: a sealed light-transmitting envelope; a combustion-supporting gas filling in said envelope at a pressure above atmospheric, the quantity of said gas being at least about 2 mgs. per cc. of envelope volume; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium.

2. A photofiash lamp comprising: a sealed light-transmitting envelope; an oxygen gas filling in said envelope at a pressure above atmospheric, the quantity of said gas being at least about 2 mgs. per cc. of envelope volume; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium.

3. A photofiash lamp comprising: a sealed light-transmitting envelope; an oxygen gas filling in said envelope at a pressure above atmospheric, the quantity of said gas being at least about 2 mgs. per cc. of envelope volume; a quantity of filamentary zirconium, having a cross-section of between about 0.4 10- sq. in., to about 1.8)(10 sq. in., disposed in said envelope, the ratio between said filamentary zirconium and the weight of said gas being substantially in stoichiometric balance; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium.

4. A photofiash lamp comprising: a sealed light-trans mitting envelope; a combustion-supporting gas filling in said envelope at a pressure above atmospheric; a quantity of filamentary zirconium, having a cross-section of between about 0.4)(10 sq. in., to about 1.8 10- sq.

in., disposed in said envelope, the ratio between said filamentary zirconium and the Weight of said gas being substantially in stoichiometric balance; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium, said lamp producing a total light output of about 1000 lumen seconds per mg. of the combustion-supporting gas.

5. A photoflash lamp comprising: a sealed light-transmitting envelope; a combustion-supporting gas filling in said envelope at a pressure above atmospheric, the quantity of sai gas being at least about 2 mgs. per cc., of envelope volume; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope and in operative relationship with respect to said filamentary zirconium, said lamp producing a total light output of about 1000 lumen seconds per mg. of the combustion-supporting gas.

6. A photo-flash lamp comprising: a sealed light transmitting envelope; a combustion-supporting gas filling in said envelope at a pressure above atmospheric, the quantity of said gas being at least about 2 tags. per cc. of envelope volume; a quantity of filamentary zirconium, having a cross-section of between about 0. l l0 sq. in., to about 1.8x sq. in., disposed in said envelope, the ration between said filamentary zirconium and the weight of said gas being substantially in stoichiometric balance; and ignition means disposed in said envelope and in operative relationship with respect to said filamentary zirconium, said lamp producing a total light output of about 1000 lumen seconds per mg. of the combustionsupporting gas and a total light output per unit envelope volume of at least about 2000 lumen seconds per cc.

7. A photoflash lamp comprising: a sealed light-transmitting envelope; an oxygen gas filling in said envelope at a pressure above atmospheric, the quantity of said gas being at least about 2 mgs. per cc. of envelope volume; a quantity of filamentary zirconium, having a cross-section of between about 0.4)(10 sq. in., to about 1.8 l0 sq. in., disposed in said envelope, the ratio between said filamentary zirconium and the weight of said gas being substantially in stoichiometric balance; and ignition means disposed in said envelope and in operative relationship with respect to said filamentary zirconium, said lamp producing a total light output of about 1000 lumen seconds per mg. of the oxygen gas and a total light output per unit envelope volume of at least about 2000 lumen seconds per cc.

8. A photoflash lamp comprising: a sealed light-transmitting envelope of glass; a combustion-supporting gas filling in said envelope, the initial fill pressure being above atmospheric and the ratio of instantaneous peak pressure to initial fill pressure being less than 2 to l; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope in operative relationship with respect to said filamentary zirconium.

9. A photoflash lamp comprising: a sealed ight-transmitting envelope or glass; an oxygen gas lilling in said envelope at a pressure above atmospheric and at least one half of the pressure which said envelope can withstand safely upon firing; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope in operative reiationship with respect to said filamentary zirconium.

10. A photoflash lamp comprising: a sealed light-transmitting envelope; an oxygen gas filling in said envelope, the initial fill pressure being above atmospheric and the ratio oi instantaneous peak pressure to initial'fill pressure being less than about 2 to 1; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope and in operative relationship with respect to said filamentary zirconium.

l l. A photoflash lamp comprising: a sealed light-transmitting envelope; at combustion-supporting gas filling in said envelope at a pressure above atmospheric and at least one-half of the pressure which said .envelope can Withstand salely upon firing; a quantity of filamentary zirconium disposed in said envelope; and ignition means disposed in said envelope and in operative relationship with respect to said filamentary zirconium.

12. A photoflash lamp comprising: a sealed light-transmitting envelope; at combustion-supporting ga filling in References Cited in the file of this patent UNITED STATES PATENTS Re. 18,678 Ostermeir Dec. 6, 1932 2,272,059 De Margitta Feb. 3, 1942 2,272,779 Sarbey Feb. 10, 1942 2,315,099 Van Liempt Mar. 20, 1943 2,810,283 Cohen et a1 Oct. 22, 1957 2,813,411 Johnson Nov. 19, 1957 2,865,186 Anderson et al. Dec. 23. 1958

Claims (1)

1. A PHOTOFLASH LAMP COMPRISING: A SEALED LIGHT-TRANSMITTING ENVELOPE; A COMBUSTIION-SUPPORTING GAS FILLING IN SAID ENVELOPE AT A PRESSURE ABOVE ATMOSPHERIC, THE QUANTITY OF SAID GAS BEING AT LEAST ABOUT 2 MGS. PER CC. OF EN-

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