The turn-on field distribution of emission sites in carbon nanotube (CNT) film are measured by counting lighting dots. This provides a convenient method to characterize the field-emission uniformity of a CNT cathode. With this method, a quantitative characterization of the emission-uniformity improvement of a printed CNT film after a conditioning is obtained. The turn-on field distribution of an array of CNT dots in a pixel also can be measured with this method. (C) 2008 American Vacuum Society.