Snipped by me for focus.
I suspect that some forensic work would actually be better carried out in the dark. A comprehensive article here has this as its opening paragraph:
"Ultraviolet Light Analysis
Ultraviolet (UV) light technologies are used for multiple purposes in forensic investigations, including authenticating paintings and other fine art, authenticating signatures, analyzing questioned documents , illuminating latent fingerprints at crime scenes and trace evidence on clothing, analyzing ink stains, and revealing residual stains of body fluids."
The rest of the article is technical but very interesting. It doesn't actually say that the presence of other light would reduce the efficacy of the technique, but I suspect it might. I think it is quite likely that the Spanish authorities would have used this technique on the camper van at some stage. If they did, they could have been quite open about it - it is a bog standard procedure. Instead, their explanations have done nothing but raise eyebrows.
I think this technique can only be carried out under black room conditions.