 The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets, or other phenomena.CRTs have also been used as memory devices, in which case the visible light emitted from the fluorescent material (if any) is not intended to have significant meaning to a visual observer (though the visible pattern on the tube face may cryptically represent the stored data).In television sets and computer monitors, the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster.