When it's lightning out a person can be struck from lightning even when the lightning is as far as 5 or 10 miles away.
The closer the lightning is to you the higher chance you have at getting struck by the lightning.
And the closer you are to the lightning the higher chance you have at getting killed or severely injured as a result of the lightning.
When it's lightning you should stay indoors until the lightning storm goes away and if you're outside walking or riding a bike etc you need to seek shelter as soon as possible.
Lightning kills about 51 people each year and another 100 or so people get injured as a result of being struck by the lightning.