Patent GB-1525726-A (GB)
Title: Photoflash lamp array having radiation switches and flash indicators
IPC: G03B15/04
Filed: 1975-09-09
Abstract: 1525726 Photo-flash lamp arrays GENERAL ELECTRIC CO 9 Sept 1975 [30 Sept 1974]  37023/75 Heading G2X A flash array comprising a plurality of lamps has circuitry for firing them sequentially by means of radiation-actuated switches, and also has indicators which show which lamps have been flashed. As shown, the multiple flash-lamp array of Fig. 1 is divided into an upper group 21 and a lower group 26 of four lamps each. A plug-in connector tab 18 (or 18') is provided at the upper and lower ends of the array, so that it can be plugged either way up into the socket 19 of a camera or flash adapter. In whichever way it is plugged in, only the upper four lamps can be flashed, these being farther from the lens axis, and thus minimizing the "red-eye" effect. Fig. 3 shows the circuit board, which can be contained within the housing of the lamp array, behind the lamps and their reflectors. The socket 19 has contacts 38, 37 and 37', the latter two being connected together. These three contacts engage terminals 32, 31 and 33 (or 32', 31' and 33') on the circuit board. A firing pulse source 39 is connected to the contacts 37, 38, the pulses being synchronized with the opening of the camera shutter. The board is shown with tab 18 plugged into socket 19, and the conductor run on the board from terminal 31 connects to one lead wire of each of the eight lamps (as at 41, 42, 43, 44). A conductor run from terminal 32 connects to the other lead wire of lamp 24 (which has lead wires 24a, 24b), and terminates at radiation-actuated switch terminals 46, 47, 48. The respective radiation switches 66, 67, 68 are located closely behind lamps 24, 25 and 23, so that they can receive radiation from the lamps through small openings in the reflectors. When a lamp is flashed, the radiation acts on the switch to change it from an open circuit or high resistance to a closed circuit or low resistance. Thus as each lamp is flashed it becomes an open circuit between its lead wires, so that the next firing pulse is applied to the next lamp. Thus all four lamps will be fired in sequence. A conductor run on the board from terminal 33 connects to lamp 28, which is the first lamp to be flashed when the array is turned around and plugged in the other way up. Since contacts 37 and 37 are shorted together, terminals 31 and 33 are shorted together, thus shorting the input to the lower group of lamps, which consequently do not operate. The lower part of the circuit board is a reverse mirror image of the upper part, so that when the array is plugged in the other way up, all the same considerations apply to the other group of lamps. Each lamp has associated with it a flash indicator, visible from the rear of the array, and comprising an area which changes colour in response to radiation from the lamp. Thus the indicators show at a  glance which lamps have been flashed and which have not. Openings 72 are provided in the circuit board behind each lamp to allow the radiation to pass through to the indicator, which is a radiationsensitive plastic positioned behind the circuit board and visible through a transparent sheet forming the back of the housing. The radiation-sensitive plastic may be in the form of strips (80) Fig. 5 (not shown) attached to a sheet of metal foil (78) carried on a paper sheet (77) having openings (79) through which the colour of the indicator may be observed. In the position in which the lamp is flashed, the radiation switch is positioned adjacent the upper part of the lamp, and the flash indicator adjacent the lower part, since more radiation is produced in the upper part of the lamp, and it is considered more important to ensure proper switch functioning than proper indicator functioning.