I haven't seen a marked TV detector van for for over 25 years. I'd kind of assumed that digitisation of the TV licence records some time before that, as as well

I haven't seen a marked TV detector van for for over 25 years. I'd kind of assumed that digitisation of the TV licence records some time before that, as as well as migration away from CRTs, meant that sending reminders/demands was simply more effective. And I'm really not sure I believe that they correlate room light fluctuations with broadcast programming, or even that this is technically/economically feasible. Sounds more like disinformation to me.