The value of a carbon arc with properly chosen graphite electrodes and operating conditions as a reproducible high-temperature source of radiation has been recognized for a long time. Many studies both in this country and abroad have shown that the crater of the positive electrode has a brightness temperature at wavelengths near 6500 Å which falls very close to 3800°K, with a deviation of probably less than ±20°K. However, a number of scattered observations have shown small effects of operating conditions such as current, angular arrangement of electrodes, and size and composition of electrodes. New studies of these variables, including measurements of spectral and total radiance, have clearly defined operating conditions under which the crater radiates like a blackbody at 3800°K over the entire wavelength range 3000°-42 000 Å except for molecular radiation at specific wavelengths.
M. R. NULL and W. W. LOZIER, "Carbon Arc as a Radiation Standard," J. Opt. Soc. Am. 52, 1156-1161 (1962)