Is it against the law for cyclists to ride on main road without lights?

I would like to know whether it is against the law for cyclists to ride on main roads without lights?

I attend a local church on Sunday evenings. I frequently come across cyclists in dark clothes who have no lights and are virtually invisible. I asked a young man about it tonight and was told to “Shut up you miserable woman!” I do not think there is much we can do about this, but it does worry me in case I knock one over one day. I understand that I would be held accountable not the cyclist.

What do others think?