TonyV, I agree that if an agency/authority, any authority/agency, takes up the complaint for pursuance against the neighbour then that presumably confirms that a valid complaint has been brought. Artificial light which varies/flashes/whatever can be extremely disruptive whereas constant light is far less so and probably for most people hardly at all unless of the spotlight type. There is no evidence that I know of which shows that sleeping in partly lit conditions is detrimental and some people prefer it. Millions of people have no choice but to sleep in low light (street lights) and others in full daylight (summertime in high latitudes north and south) and there is no suggestion that there is serious suffering as a result (that I am aware of).
I know of a person who has spent something like 40 years trying to get the local authority (separate approaches to many different departments over the years, usually on the principle that the right hand doesn't know what the left hand has already done/decided), local politicians, etc., etc. to get a neighbour's trees cut down, so far unsuccessfully. The main reason appears to be that she objected/objects to the new ownerhip per se. I recall living in India where they celebrate weddings for a week with the street taken over by one or more marquees and loud music blaring pretty much non-stop. I got far less sleep than normal for a few nights but sort of marvelled at the tolerance shown by people over a large radius around (I was two houses away). Maybe the lack of tolerance is the main problem with many neighbourly disputes in the UK ?