Okay, after rereading it I notice that my original post is a little lacking in detail, so let me form it into a more concrete problem:
Say that there's a sphere of radius R surrounded by empty space but fill with gas X and at temperature T. What is the total power emitted to the surrounding...
How does the emissive power for a gas depend on temperature? Is there a conceptual generalization (along the lines of Planck's Law) for the radiation of power from a partially transparent material or must a specific emission spectrum be chosen?
Thanks