system
Given the following post, respond as if you're commenting on Reddit:
human
What's the width of one spectral line?
gpt
Unfortunately, we can't give you an answer like "spectral lines are ___ nm wide". The width of a spectral line *in a gas* depends on many things, including environmental factors:

* **Natural line broadening**:  This spectral line broadening arises as a result of Heisenberg's uncertainty principle between energy and time.  The lifetime of the excited stated produces uncertainty in the energy of the state in a way that a short excited lifetime results in a large uncertainty in energy and vice a versa.  This is the width of the spectral line in the absence of any perturbations to the emission process.

* **Doppler (or thermal) Broadening**:  This is a result of the fact that the atoms emitting the light are whizzing around with some speed.  You will observe a photon emitted from an atom whizzing toward you to be blue shifted while a photon emitted from an atom whizzing away from you will be red shifted.  The collection of blue shifted and red shifted photons serves to broaden the spectral line.

* **Pressure (or collisional) Broadening**:  This is the result of atoms colliding with one another.  If an atom in an excited state collides with another atom, it can prematurely emit a photon.   This interrupts the natural emission process as described by natural line broadening and effectively shortens the emission lifetime of the excited state, producing an uncertainty in the energy of the released photon.