Don't turn on the light!

The German couple, who own one of the Shetland ponies I look after, are here for a few weeks, and this morning Ollie and I went round to see them and have a lovely relaxed outdoor breakfast with them. The swallows have realised that there is nobody about in the ponies' shed at the moment, and have set up home on the light! I didn't turn the light on and electrocute them but unfortunately they are probably all blind now, from the flash! Oh God, I hope not, something else to feel guilty about!