Walking your dog in the dark can be a bit scary, especially if you go off the beaten track where there are no street lights. What I do is put a red rear bicycle light on Ben's collar, and take two wind up torches with me. I can see him as he is sniffing around the hedge bottoms, and people think he's so sweet with his illumination. I know you can buy dog collars with lights incorporated into them, but I don't think they are bright enough for a big dog with long fur.
Ilona