CRT televisions use electron guns to fire electrons at color phosphors on the screen which emit the light of varying frequencies to produce an image. They can scan row by row or column by column depending on the standard of the broadcasting signal though modern models have circuitry that can read the broadcasting codec and adjust the electron gun to match the scanning standard of the broadcast. LCD, LED, and plasma screen televisions can either use millions of tiny light bulbs that switch on and off in a sequence to generate the image or focusing mirrors to direct the output of a few light bulbs to certain sectors of the screen in sequence to produce the image. The orientation of the scanning of these flat screen televisions also depends on the broadcasting standard though all flat screen models can be set to automatically adjust to the broadcasting standard. But these electronic scanning methods only seem to work if there is only one video signal entering the device. How do some televisions display multiple video signals with each one having their own division in the screen?