Photodoto » Blog Archive » Quick tip: Flare control:

When you're shooting towards a bright light source, like the sun, light may hit the lens directly. When that happens, flare will inevitably appear in your photos. Flare introduces strange reflections and robs contrast from your images. Lens hoods control flare by shading the lens.

Photodoto share a great tip about how to avoid lens flare if your lens hood isn't quite cutting it for the angle you're shooting.