I am trying to understand what determines to what degree energy from a "hot" object is emitted as characteristic radiation or blackbody radiation.
For example in a gas discharge lamp, a considerable amount of the energy emitted by the hot gas is clearly emitted as characteristic radiation, but some of it must also be emitted as blackbody radiation.
Another example would be a gas, such as a greenhouse gas, e.g. CO2, in the atmosphere absorbing, terrestrial radiation. When discussing the greenhouse effect, it is often simply stated that this energy is emitted as blackbody radiation by the atmosphere. Is emission of characteristic radiation according to allowed transitions not relevant?
*By characteristic radiation I mean line emission i.e. emission due to electronic, rotational, vibronic... transitions.
*The question was prompted by a project on the greenhouse effect, so I am mainly interested in whether it is accurate to say that the energy absorbed by the atmosphere from the thermal radiation of the earth, is subsequently emitted as blackbody radiation. John Rennie's answer seems to suggest this is not the case. If so, why is the greenhouse model explained in terms of the atmosphere doing precisely that?