Neon - Camera as a Spectrograph

A spectrograph is an instrument for measuring the frequencies of a light source. I would guess that most spectrographs are calibrated by using known light sources. So for example, if you measured the frequency of an unknown light source and it contained the frequency of excited neon, then you could say that the unknown light source contained neon.

At the National Museum of Natural Science in TaiZhong they have a display of several exited gases. I took a picture of what I knew was neon.

 
























I then cut the red of the neon source and can overlap it on a picture of an unknown source with MS Paint and see it then matches up. For example, this Christian cross is not a neon light.

Whereas this TaiShan Buddhist Temple's backward twisted swastika is neon.

This method only works if the camera used is the same one used to take the reference shot. I know this cross is neon but the photo was taken with one of my past cameras.

There is still the problem of different glasses(with different absorption characteristics) and maybe the gas in the tube in not totally neon, but this method seems OK.