Interesting about the UV, asked by brother who is a Race mechanic, and he's never heard of that, but they change the oil every few hundred miles tops!
I have to admit my only 'test' in 25 years of changing petrol engine oil is looking at and sniffing it.
By frequent changing I hope to get it still partially clear and not smelling to much of fuel or burnt oil.
Regular 6k is noticeably more like that than the rancid stinky black stuff you get out after 18k.
But yes, mainly for personal satisfaction....