How can I ask for a security light to be adjusted when my neighbour says it makes her feel safer?

The new light switched on while we were talking over the fence, and my neighbour said, “You can see why I wanted it.”

I could. Her back steps were much easier to see. From my bedroom, though, each activation lights up the ceiling above my bed. We live in England, and I have started waking when she lets the dog out late at night.

I asked if she could change the angle. She replied that the installer had set it up and she didn't want to touch it. Then she suggested blackout curtains. My existing curtains have a gap at the top, and I could replace them, but I am reluctant to start there before finding out whether the light can be adjusted properly.

The [government's guidance on artificial light nuisance](https://www.gov.uk/guidance/artificial-light-nuisances-how-councils-deal-with-complaints) includes domestic security lights, but it doesn't give a universal brightness threshold that makes every intrusive light a legal nuisance. I don't want to open with a claim I can't establish.

How do I explain the bedroom effect without sounding as though her safer steps don't matter? I'd be happy to arrange a time when she can see it from my side; I don't want to become the person suggesting settings on equipment neither of us understands.