A photoflash unit comprising a plurality of high voltage type flashlamps mounted on a printed circuit board containing circuitry for sequentially igniting the flashlamps. A plurality of electrically conductive reflectors respectively associated with the flashlamps are disposed between the lamps and the circuit board, with each reflector having an aperture in alignment with a corresponding aperture in the circuit board. Connected in series with each but the last lamp of the array is a radiant-energy-activated disconnect switch comprising a strip of electrically conductive heat-shrinkable polymeric material which is attached at both ends to the circuit board so that the midportion of the strip bridges a respective one of the apertures therein. A sheet of electrically insulating material is interposed between the reflectors and circuit board to prevent shorting therebetween. A plurality of deformations, such as dimples, are formed in the insulating sheet for spacing the sheet from the disconnect switch strips.