The carbon arc in argon, even at atmospheric pressure, possesses excellent qualities as a radiation standard, in comparison with which the so-called standard arc in air is much inferior. A further improvement is to be expected if the rapid intensity fluctuations common to all forms of the arc can be overcome. In its most easily attainable form, the arc is free from band structure and capable of a crater temperature of about 4300°K, under elevated pressure.
ROBERT R. JAYROE, JR. and R. G. FOWLER, "Carbon Arc in a Controlled Atmosphere as a Radiation Standard," J. Opt. Soc. Am. 57, 513-516 (1967)