In certain light conditions you and/or your adversary may appear to each other as only a silhouette-a solid outline in the semi-darkness against a slightly brighter background. Or perhaps as a "shadow" behind a curtain etc. Some postures and moves will alter your silhouette and thus alert your opponent to your maneuver thus giving them vital moments to counteract you. On the other hand, there are certain postures and sets of moves that hardly effect your silhouette at all-from the viewpoint of your adversary.
Such moves are advantageous and thus it is suggested that you become familiar with the effects that all moves have on your theoretical sillhouette from different angles. This endeavour is in line with general theory of the Shhhhh martial art: the principle of becoming as deeply aware of the possible movements as possible from many different perspectives and restrictive situations.
It is possible that even in ordinary light, the brain may detect "silhouette altering moves" faster than movements that do not significantly alter ones silhouette. If so then training in this area (increasing your awareness in this area) may be very useful in giving you the edge in hand to hand combat and in other spheres of importance.
Another aspect to silhouette fighting is the ability to quickly and accurately interpret your adversary's silhouette. What does there outline tell you about their hidden posture, their next *possible* moves and outline changes that indicate their move. As your visual sense is limited by the lighting conditions in such a situation we should already be prepared, via previous training, to utilize your other senses more intensly. Senses such as hearing, smell and touch should automatically be paid attention to more when your visual sense is impaired for whatever reason.