 Beryllium production saw a rapid increase during World War II , due to the rising demand for hard beryllium @-@ copper alloys and phosphors for fluorescent lights . Most early fluorescent lamps used zinc <unk> with varying content of beryllium to emit greenish light . Small additions of magnesium tungstate improved the blue part of the spectrum to yield an acceptable white light . <unk> @-@ based phosphors replaced beryllium @-@ based phosphors after beryllium was found to be toxic . 
