Remember that flame is a light source. A candleflame will light up anything within a foot or two, and will cast a dim glow further. A campfire will light the faces of those around it - from below if they are sitting close to a low fire. A large bonfire will cast a strong directional light upon people around it, throwing long shadows. A good reference source is invaluable to help you identify just what is in light and what is in shadow when fire is part of a scene.