Lamp radiation spectrum
 

Hi,
I'm studying the properties of an incandescent lamp. I tried to simulate it with a direct radiation flux imposed in the boundary condition on the outer surface of the lamp. The thermal settings of the wall is set to 'Mixed'. However I don't know which is the spectrum associated with this radiation flux. I read that, since I am using a DO model, the spectrum is supposed to be like a gray body (which in turn it behaves like a black body with different radiance). The problem is hence that the spectrum of a black body is highly dependent on its temperature and therefore I am wondering how it is calculated in fluent. Is it calculated based on the wall temperature or it uses a different reference?
Thanks in advance