my advice for what it's worth is that a beam of only 100 yards is totally unsuitable for running any dog after live quarry, especially a young inexperienced dog, a rabbit can soon disappear out of this this range leaving your dog very vulnerable if it pursues it out of range in the dark, just wondered what your reason was for limiting yourself and your dog to such a small beam, i've used a cluson/lazerlite lamp for years which is ideal and you can get some very small batteries now for easy carriage, years ago i experimented with a small pencil beam and found it totally unsuitable for lurchers chasing rabbits, you may hear lots of crashes and squeels as your dog runs the rabbit out of the beam, hopefully luck will be on your side for your dog, forget the convenience of sticking something small in your pocket and give your dog a better chance at catching the rabbit and avoiding injury, those small lamps are only suitable for something like airgun shooting.