Light Tricks and Traps (DMG)

Sometimes a fire or light source can be used by intelligent creatures as a diversion or trap. One trick is to build a fire and then set up camp away from it. The fire attracts whatever is likely to show up in the area, allowing the characters the chance to ambush the unwary. This is a favorite tactic of many evil and warlike races such as orcs, bugbears, goblins, and bandits. It is also a trick used by adventurers to lure monsters away from their real camp, although this is somewhat dangerous.
Since fires are often used to determine the size and possible strength of an enemy, dull-witted creatures and nervous player characters can be frightened away by building a large number of campfires in an area. The enemy, counting these fires, decides there is a huge force camping here for the night and becomes frightened enough to leave. In reality, each fire might have but a single man or orc tending it.
Although the radius of a light source is the limit a character can effectively see using that source, it is not the absolute limit. The light doesn't just end there as if it had hit a brick wall. Beyond the radius of the light, there will still be flickering shadows, reflected eyes, and perhaps glints of metal. Now, some of these may be nothing more than the overactive imaginations of the player characters; others may be real threats! The DM can use this unknown factor as a tool to build suspense in his game.