In a coal fire, the pockets formed by coals appear brighter than the coals themselves. Is the temperature of such a pocket higher than the surface temperature of a glowing coal?
The temperature of pockets formed hy coals are not appreciably different from the surface temperature of glowing coals.
However, the pockets formed by coals act as cavities. The radiations from these cavities are black body radiations and so have maximum intensity. Hence, the pockets appear brighter than the glowing coals.