Ours are spooked by a torch most of the time, but during lambing they soon get used to it, so they don't get up. I don't like to disturb them when they're all lagered up (ewes round the outside, lambs tucked safely in the middle). I know where they'll be then, because at that time of year they sleep at the highest point of our land, unless they're in their shelters.
I use a head torch to see my way around, then a powerful torch to flash over the sheep. Those giant torches hurt their eyes, so shouldn't be shone directly at them anyway. Then I stand and slowly check with the big torch round all the field edges for eyes reflecting (our sheep are black so can only see the eyes). If I'm worried then I'll go around the whole perimeter. Really we only check them at night during lambing, or if I hear someone bawling, which usually means a problem.
I think yours will soon get used to you checking with a torch through the winter. If you have only a few sheep, then you can easily count them and only if there's one missing go searching. Or if it's foggy you just have to traipse round.