Is there an effective way to stop light coming in at the edges of a bay window?

[Tory79]

Considering moving DS(3) into a different bedroom, it has a lovely bay window but light just pours in round the curtains! ( I know this because it's currently my room!)

Is there a good way to block the sides off so it stays dark?

Blackout blinds on all the panes.
Box pelmet and blackout lining to the curtains.
Make sure the curtains come to the very edge of the windows and that there is an overlap where they meet.
Gro-blinds on each of the windows.

Wider curtain rails and curtains.