I have recently performed an old experiment using a spectrograph with a photographic film having a helium spectral lamp as a source of light. The picture attached below shows the developed photo of a helium spectrum. I am not going to lie, but I am a bit confused with the result. I want to plot a dispersion curve for helium of wavelength versus distance of spectral lines from an arbitrary zero point to use it in the future in identifying more complex atomic spectra. Unfortunately, I am not able to identify these lines to assign them corresponding wavelengths from some scientific database. I have a guess that the strong line a little bit on the right from the photo's center can be the yellow spectral line. But having a look at some helium spectra on the internet, I am not completely sure about that and other guesses. I could use some help of people who are more experienced in this sort of stuff and who can notice something what I have overlooked.
I think the heavy wide line at the left of your spectrum is the unresolved helium triplet at 587.56148, 587.56404 and 587.59963 nm. Therefore, long wavelengths are at the left side of your spectrum.
Using one of my homemade echelle spectrographs and a helium discharge tube, here is the two dimensional spectrum, called an echellogram, that I acquired for the light from a helium discharge tube:
The energized discharge tube emits light that appears yellow, to me, as expected from the helium triplet being helium’s most intense visible emission feature.
This next echellogram is annotated to show the helium line wavelengths in angstroms:
Short wavelengths are at the left and, in each grating order (‘arc’), at the bottom. In this image, the helium echellogram is an overlay on a composite echellogram prepared from tungsten and deuterium lamps in the Ocean Optics DH-mini UV-VIS-NIR Lightsource. This just makes it easier to see where the spectral lines are located in the echelle grating’s diffraction orders.
The strong helium emission lines are from the standard NIST online tables
The wavelengths in the table are in angstroms.
Hopefully, this will help you assign the rest of the lines.