Abstract: A photoflash unit is designed to have a plurality of lamps fired individually and in sequence includes a plurality of switching devices capable of being easily activated by radiant energy generated during flashing of the lamps. Initially, the switches have a high resistance ("off" position) and after being activated by radiation, they undergo a chemical change to a conductive state ("on" position). The switches are prepared from compositions which impart improved shelf life under conditions of high relative humidity and include a light absorbing, heat transmitting protective coating having absorption characteristics in the range of 3000-5500 A.