Complex sentence: The working distance is from the point of view of the user of the flashlight; the beam may be visible against a dark background for many times this distance, especially if the observer has night-vision equipment.
Split into simpler sentences: The working distance is from the point of view of the user of the flashlight. A light directly pointed at an observer may be visible against a dark background for many times this distance, especially if the observer has night-vision equipment.