A family group of three became benighted when they ran out of daylight and only had the torch from a phone. A small scale search was organised, and during this we managed to activate SARLOC, which located them on the ridge. They were escorted down by team members.
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.