This paper, using a self-medium with field for light and the medium to travel concurrently at the speed of light in free space without the other media, proposed by Ohki’s papers in viXra and ResearchGate, proposes whether or not new electromagnetic thermal constant in an ideal photon gas law is different to the existing Boltzmann constant k(B) in mechanical particle system. Besides, when given a solar radiant volume filled up electromagnetic mass passing through at the speed of light, this paper shows an estimation of a beam bungle mass passing in the volume product of a solar radiant surface and radiant length of 1 m on a surface of the Sun. When given an ideal photon gas law that constitutes of the volume V uniformed with lots of cells equipartitioned with temperature T, N number of photons and internal pressure P in the volume, new electromagnetic thermal invariant constant b proportional to product of the temperature and the number, variable with respect to z on an radiant axis is each volume V, temperature T, pressure P, and a set product of number N and the temperature T times b, so that we can estimate the constant b and the mass. Moreover, on the basis of 4 significant-digits arithmetic, given two volumes are: One solar radiant volume locates on solar surface of the Sun, the other volume locates on satellite over earth so that we can get only solar surface temperature T(s) with 4 digits and a radiant power flux density ɸ(We) on radiant surface the satellite, respectively. Under those above-mentioned conditions, when applying an ideal photon gas law in dynamic volume for light to pass through the volume, the result of estimation shows a ratio of the constant b to the Boltzmann constant k(B) is surprisingly estimated 99.94%. Besides, we can get a bundle energy divided solar radiant energy passing the volume by the passing number, so that we can get the bundle mass under a postulation that a beam bundle mass m is equal to the bundle energy E times the electromagnetic constant εμ, that is, reciprocal of the speed of light square, m = ε μ E, proposed by Ohki. Under the postulation, we can get estimate a solar beam bundle mass passing through a radiant surface on the surface of the Sun, given a radiant length of 1 m, is estimated, 2.956E(- 45) kg