A man was reported overdue after seperating from his walking companions at Esk Hause to take a different route back to Langdale. He was reported overdue when it went dark and he hadn't returned. It was known that he had no torch and would most likely have stopped moving at this point. A search was being organised when he turned up, having been aided by another walker who had found him and helped him down
What ever time of year, always carry a torch. You never know when or why you may be delayed.
When it goes dark in the hills, it usually goes VERY dark! There's little ambient light unless you are lucky to be out when there is a good moon and little cloud.
It's worth carry a set of spare batteries as well. If you're lucky they'll be the same size as other devices you might be carrying such as GPS.
Modern LED torches are very reliable, and batteries last a long time, and it's well worth considering a headtorch in favour of a hand torch, leaving your hands free.