The colorimetric properties of the conventional arc lamp and LED are calculated and analyzed by using the colorimetry theory. Comparing to the conventional arc lamp used as projection light source, LED illuminator has higher efficiency of the spectral power and better ability of color display. It can reach sRGB standard widely used by digital projectors. The single-color LED driven by temporal pulses will produce high-brightness projection display with saturate colors. Therefore, LED can take place of conventional arc lamp to satisfy the colorimetric requirement of the projection display.