I don't know how to tag rainbow arcs in the rigth part of the picture.
Wiki page for lens flare states:

The following are NOT lens flares: Rainbow-colored arcs that partially or entirely encircle the light source. These are called halos, and are not camera artifacts.

However, wiki page for halo says otherwise:

Not to be confused with halo-like artifacts of light caused by bright light sources interacting with the camera lens. The latter is a lens flare.

Which of these statements is more credible?

Why are you looking at the halo wiki on Danbooru? That quote links to Wikipedia. We use the tag halo for other things.

I'm not sure what other tag is more appropriate to use so I won't comment on that.

HyphenSam said in comment #2628246:

Why are you looking at the halo wiki on Danbooru? That quote links to Wikipedia. We use the tag halo for other things.

I'm not sure what other tag is more appropriate to use so I won't comment on that.

So the optimal solution would be to use a halo_(optical_phenomenon) tag, if Danbooru had one? There are 700+ posts that have both tags (lens_flare rainbow), and many of them depict the same optical halo, e.g.:

• post #160236
• post #221806
• post #695626
• post #1522232
• post #10612362

etc, etc.