I know that there have been other papers published, but I was specifically looking for the one referenced by Bill Bryan, an undersecretary at the Homeland Security Department, in the press briefing today (4/23/2020).
As I recollect Bryan announced that work done by the Science and Technology section of DHS, had found that exposure to strong sunlight, particularly UV, shortened the half-life of Sars-Cov-2 significantly. (He also discussed bleach, IPA, and disinfectants, but that's not my focus for this Q)
If I can find this research, it might reveal if the "sunlight exposure" was natural sunlight or artificial. The key difference being that artificial (or laboratory sunlight) tends to also contain UV-C which is highly destructive*, whereas natural sunlight has almost no UV-C (thankfully to the earth's atmosphere)
- Laboratory sunlight can be equipped to absorb or diminish the UV-C, so I'd be looking , in the research, for actual measurements of the UV-A, UV-B and UV-C used to "attack" SARS-CoV-2 assay.