When the lights go out, you don’t always see it.

It’s not like being at the theatre, where the house lights zip down and the stage lights go up; where there’s always someone front of house with a torch to guide you if you need it. And it’s not like drawing a blind against the glare of the midday sun: a gentle shade against unbearable brightness.

Sometimes – when the lights go out – you don’t even know it’s happening until the darkness is so complete that you can’t tell whether your eyes are o...