I think it was bad weather that disorientated him rather than the dark. If you have ever been on a Devon moor in bad weather you might know how poor the visability can be (I have been driving across Exmoor at Rayleighs Cross and had to get out of my car and run up the road to see where the junction is that I need to take because I couldn`t even see the cat`s eyes or the signpost and I know that road like the back of my hand). He was only a trainee after all.