Is there a bike light law?

I have lights. I use them. But I don't think it makes me any safer. In fact I would argue the opposite.

I'm going down the road and I can see a car at the junction ahead. With lights I might presume they see me. It can turn out they haven't and you may be going to fast to brake in time. Without lights I will presume they haven't and act accordingly.

Agreed.