Patent GB-738412-A (GB)
Title: Improvements relating to electric lamps for use in flash photography
Inventor: CUMMING HARRY WYNDHAM LISTER
IPC: F21K5/08
Filed: 1953-02-20
Abstract: 738,412. Discharge lamps. SIEMENS ELECTRIC LAMPS & SUPPLIES, Ltd. Feb. 19, 1954 [Feb. 20, 1953], No. 4849/53. Class 39 (1). A low-voltage flash tube comprises a gasfilled tube 12 of heat-resisting glass or quartz, an anode 11, a cathode 13 and a trigger electrode formed by a metal strip or wire 17 wound round the outside of the tube, wherein the cathode 13 is activated with barium metal, the bore and effective gas filled length of the tube are less than 8 mm. and 200 mm. respectively, and the pressure of the gas filling is less than 60 mm. of mercury, triggering with a capacitor voltage of the order of 250 being attained. In the construction shown in Fig. 1 the tube 12, having a brass screw cap 10, is straight and has an effective length of about 60 mms. and for most of its length a bore of some 4 to 6 mms. In the region of the cathode 13 the tube 12 is enlarged to have an external diameter of 10 to 11 mms. The cathode 13 consists of a small cylinder 14 of nickel activated with barium metal with a tungsten supporting and feeding rod 15. The anode 11 is of tungsten and the distance between the inner ends of the anode 11 and cathode 13 is between 40 and 50 mm. The overall length X of the tube is about 80 mms. The tube is filled with xenon at a pressure of some 40 to 50 mms. of mercury and the trigger electrode 17 is formed of nickel wire, the rated capacitor voltage being 250, the trigger voltage being some 2000 to 3000, and the maximum loading being 30 joules. In the construction shown in Figs. 2 and 3 the tube 12, similar to that shown in Fig. 1, is mounted on an International Octal base 18 inside a glass cover 22 fixed to the base, an extension 19 of the supporting rod 15 being connected to the pins 7 and 8 of the base, the anode 11 being connected by supporting and feeding members 20 and 21 to the pins 2 and 3, and the trigger electrode 17 being connected to the pin 5. The overall length X is about 90 mms. In the construction shown in Fig. 4 the tube 12 is partly helical and has an effective (i.e. corresponding straight gas-filled) length of 90 to 100 mms., the anode 11, cathode 13, trigger electrode 17 and cap 10 being constituted similarly to the corresponding elements in the construction shown in Fig. 1. The tube 12 has for most of its length a bore of some 4 to 6 mms. and is enlarged in the region of the cathode 13. The effective distance between the inner ends of the cathode 13 and anode 11 is between 75 and 85 mms. and the overall length X is about 55 mms. The tube 12 is filled with xenon at a pressure of 40 to 50 mms. of mercury. The rated capacitor voltage is 250, the trigger voltage is between 2000 and 3000 and the maximum loading is 100 joules. In the construction shown in Figs. 6 and 7, a helical flash tube 12 is mounted inside a glass cover 22 on a 4-pin base 18, the tube being similar to that shown in Fig. 4, except that it is shaped so that the anode 11 lies at the bottom of the helical part. The cathode 13 is connected to the pin K of the base, the anode 11 to the pins A and AA and the trigger electrode 17 to the pin T. The overall length X is about 60 mms. The glass covers 22 shown in Figs. 2 and 6 are preferably frosted. In the construction shown in Figs. 8 and 9 a helical flash tube 24 similar to that shown in Fig. 4 is mounted inside a hermetically sealed outer envelope 23 containing a metal filament 25 which can be made incandescent by operation at 150 watts- 250 volts. The envelope 23 either has an inert gas filling (e.g. an argon/nitrogen mixture) or is evacuated and has a rounded light transmitting portion 40 (preferably frosted) and a portion 41 of parabolic or near parabolic cross-section which is internally aluminized to form a reflector, the flash tube 24 and filament 25 being mounted close to the principal focus of the reflector. The leading-in connections are furnished by a 4-wire foot 26 sealed into the outer envelope 23, one wire 27 of the foot being connected both to the anode 11 and to one end of the filament 25, and the remaining wires 28, 29 and 30 of the foot being connected to the other end of the filament 25, the cathode 13 and the trigger electrode 17, respectively. The. trigger electrode 17 passes through a plastic insulating sleeve 36. The wires 27-30 of the foot 26 are connected to pins 32-35, respectively, of the 4-pin base 31. The flash tube 24 is supported within the envelope 23 by supporting and feeding members 20, 21 and 37. The filament 25 is partly supported by supporting and feeding members 21 and 38, and partly by wire-supporting members carried by a glass bead 39 carried by an. extension of the anode 11.