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Oh please speak to her first (no notes, no matter how friendly your note is it always looks really pissy). If you don't get anywhere you can still go to her landlord or the council. I used to have a neighbour who'd go to my landlord first - there was a blocked drain and water was flowing onto her land. I hadn't noticed (it'd only been the case for half a day, during which I was in the whole time!) and rather than just knocking on my door and pointing it out she complained to my landlady. It upset and annoyed me - it implied to my landlord that I'm not enough a decent enough neighbour to deal with directly, which I am, and to me that she doesn't trust me to fix it without the landlord making me or that I'm not approachable. Really got my back up, I fixed it myself within an hour of the landlord notifying me.
Going over her head immediately, even if she's 'a bit odd' (not a crime last I checked) will do nothing but upset her.
You don't need to speak to either. You can contact your local environmental health dept about it. You need to say it is a light nuisance and it is materially affecting the enjoyment of your home. They will write to the owner of the property. You cold explain the situation and they may also write to the tenant.
The local authority may want to visit you when the lights are on to see what it's like, but they should write to the owner of the offending property without visiting though. It is only if they do oohing about the problem that evidence gathering will begin.
My neighbour's property has a very bright outdoor light, it's on 24-7 and I find it incredibly intrusive as it lights up the rooms at the back of my house. She's a bit odd and I feel that if I ask her to turn the lights off she won't. (I have asked in AIBU about speaking to her!)
I have contact details for her landlord (a company rather than a person), could I go to them direct and suggest they install a proper motion-activated security light instead? Or will I look mad for not going to the neighbour first? She's honestly really hard to have a conversation with.