Fundamental physical constants characterizing black body radiation. The first radiation constant is c1 = 2π.h.c02 = 3.7417749(22) x 10E-16 W m2, the second is c2 = h.c0/k = 1.438769(12) x 10E-2 m K, where h is the Planck constant c0 the speed of light and k the Boltzmann constant.