improved fuse elements used with the circuit board to provide more reliable sequential firing in a flash lamp array . the circuit board includes a lamp firing circuitry along with radiation switches connected in said circuitry and more reliable fuse elements cooperate with said radiation switches in the circuit operation . the improved fuse elements are constructed as an integral part of the lamp firing circuit pattern deposited on the circuit board at circuit locations wherein the underlying circuit board substrate has a thickness less than the substrate thickness elsewhere to enhance melting or thermal decomposition of the circuit board substrate .