Controlling two factors on which Sc-Na halide lamps depend, the coldest spot temperature in the arc tube and the Nal to Scl₃ weight ratio contained in the arc tube, the radiation power of 400 W Sc-Na halide lamps was quantitatively measured by spectro-radiometer. The experimental temperature range was 500∼800°C and the Nal to Scl₃ filling weight ratio was 1,2,5 and 7. Spectral characteristics (chromaticity, correlated color temperature, general color rendering index), visible radiation, luminous flux and radiation from Sc, Na and Hg particles, in four kinds of lamps were compared, based on measured radiation data and determining the coldest spot temperature for a lamp with outer jacket by means of measuring lamp voltage change. As a result, the data for considering Sc-Na halide lamps characteristics were get. The Sc radiation became larger as the Nal weight ratio became smaller. There was constant saturation value in the Sc radiation. The change in visible radiation, luminous flux, lamp voltage and general color rendering index for four kinds of Sc-Na halide lamps was coincident with the change in Sc radiation.