The temporal and spatial behaviour of the K I 769.9 nm solar line are investigated using several series of high spectral resolution low-noise photoelectric scans obtained at Kitt Peak National Observatory in quiet and active (plages and sunspots) regions. Corrections due to the instrumental profile were applied to yield the best line shape. A systematic center-to-limb investigation of the behaviour of the line shape was performed in quiet regions. Power and phase spectra of the main parameters defining the line shape have also been determined. Within several umbrae at different cos θ positions, an inverse C-shape or even an "S"-shape of the bisectors was found.